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The United States Virgin Islands TERRITORIAL CORAL REEF MONITORING PROGRAM ANNUAL REPORT 2023 Krampitz NM, Ennis RS, Heidmann SL, Hollander EH, Kadison E, Smith TB INDEX ii A collaboration between: The Center for Marine and Environmental Studies, University of the Virgin Islands The Division of Coastal Zone Management, USVI Department of Planning and Natural Resources The Coral Reef Conservation Program, National Oceanic and Atmospheric Administration Special Thanks To: Arrington B, Brandt ME, Byrne I, Dade LM, Durdall A, Gretta A, Harris E, Jobsis P, McKague V, Maxin S, Nemeth R, Olinger L, Parr SW, Powell J, Quetel J, Rommelfanger K, Sheeley C, Shelby A, Tierney C, and Tonge R. INDEX iii © 2025 Cite As: Krampitz NM, Ennis RS, Heidmann SL, Hollander EH, Kadison E, Smith TB (2025) The United States Virgin Islands Territorial Coral Reef Monitoring Program. 2023 Annual Report. University of the Virgin Islands, United States Virgin Islands 291pp INDEX iv INDEX OF FIGURES VII INDEX OF TABLES XVII OUR VISION 1 OBJECTIVES 1 EXECUTIVE SUMMARY 2 CORAL REEFS OF THE VIRGIN ISLANDS: MANGEMENT ACTIONS NEEDED 2 CORAL REEFS OF THE VIRGIN ISLANDS: POSITIVE SIGNS 5 IMPACTS, SCOPE, AND COMPARISONS OF THE 2023 CORAL BLEACHING EVENT 8 INTRODUCTION 13 OBJECTIVES FOR MONITORING CORAL REEFS 16 METHODS 19 BENTHIC ASSESSMENTS 19 FISH CENSUS 25 BENTHIC COMMUNITIES AND CORAL REEF HEALTH 27 CORAL COVER 28 ALGAL COVER 33 OTHER BENTHIC COVER 36 FISH COMMUNITIES 38 BLACK SPINED SEA URCHIN DIADEMA ANTILLARUM 47 SITE SUMMARIES 49 RATIONALE 49 SITE SUMMMARY ELEMENTS 49 PHYSICAL CHARACTERISTICS 50 ST. CROIX 52 INDEX v BUCK ISLAND, ST. CROIX 53 BUCK ISLAND DEEP, ST. CROIX 59 CANE BAY 67 CANE BAY DEEP 73 CASTLE 80 EAGLE RAY 87 GREAT POND 93 JACKS BAY 99 KINGS CORNER 105 LANG BANK EAST END MARINE PARK 111 LANG BANK RED HIND FISH SPAWNING AGGREGATION 119 MUTTON SNAPPER 125 SALT RIVER WEST 131 SALT RIVER DEEP 137 SPRAT HOLE 145 ST. JOHN 151 CORAL BAY 152 FISH BAY 158 MERI SHOAL 164 ST. THOMAS 170 BLACK POINT 171 BOTANY BAY 178 BREWERS BAY 184 BUCK ISLAND, ST. THOMAS 190 COCULUS ROCK 196 COLLEGE SHOAL 202 FLAT CAY 208 GINSBURGS FRINGE 214 INDEX vi GRAMMANIK TIGER 220 HIND BANK 226 LITTLE SAINT JAMES 232 MAGENS BAY 238 SAVANA ISLAND 245 SEAHORSE COTTAGE SHOAL 251 SOUTH CAPELLA 257 SOUTH WATER 263 LITERATURE CITED 269 INDEX vii Index of Figures Figure 1. Partially bleached and recovering colony of Siderastrea siderea at Flat Cay, St. Thomas (Nov. 12, 2005). .................................................................................................................................................................................................................... 3 Figure 2. TCRMP diver surveys bleached corals during the peak of thermal stress at the Meri Shoal TCRMP monitoring site, December 7th, 2023 (photo credit: N. Krampitz) ............................................................................................ 8 Figure 3. 1982 – 2023 sea surface temperature (left axis ,blue line), left vertical axis and degree heating weeks (right axis, red line) for the USVI. ............................................................................................................................................................. 9 Figure 4. Mean coral bleaching prevalence and extent at each TCRMP site in 2005, 2019, and 2023. .................. 10 Figure 5. Mean coral cover at each TCRMP location during peak bleaching in the fall of 2023 and post- bleaching sampling in the fall of 2024. ............................................................................................................................................... 12 Figure 6. A TCRMP research diver (S. Heidmann) on closed circuit rebreather records a roving fish survey at the Salt River Deep wall site, 30m/100’ depth (April 9, 2020; credit: S. Meiling). ........................................................... 17 Figure 7. Locations of Territorial Coral Reef Monitoring Sites in the US Virgin Islands. Boundaries indicate federal and territorial marine protected areas. .............................................................................................................................. 18 Figure 8. A screen grab of benthic video used for the determination of percent cover of coral reef organisms and non-living substrate. ........................................................................................................................................................................... 21 Figure 9. Sea surface temperatures and coral degree heating weeks of the US Virgin Islands from 1984 – 2024. .............................................................................................................................................................................................................................. 27 Figure 10. Mean hard coral, macroalgal (encrusting and erect), and epilithic algal community (EAC) coverage (±SEM) across all TCRMP sites during sampling from 2002-2024. ........................................................................................ 30 Figure 11. Coral cover (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2001 – spring 2024. .............................................................................................................................................................................................................................. 31 Figure 12. Coral cover (±SE) across St. Croix TCRMP monitoring sites from 2001 – spring 2024. ........................... 32 Figure 13. Mean algal coverage (±SEM) across TCRMP monitoring sites from 2005-spring of 2024. ................... 35 Figure 14. Mean benthic cover (±SEM) of gorgonians, sponges, and zooanthids from 2005-spring of 2024 at TCRMP locations. .......................................................................................................................................................................................... 37 Figure 15. A representative photo of the mesophotic wall sites on St. Croix, characterized by sloping walls, high silt loads, Agarica spp. coverage, and low fish abundance, biomass, and richness (photo credit: L. Henderson). .............................................................................................................................................................................................................................. 41 Figure 16. Fish abundance (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2003-2023. ... 42 Figure 17. Fish abundance (±SE) across St. Croix TCRMP monitoring sites from 2003-2023. ................................... 43 INDEX viii Figure 18. Nassau grouper (Epinephelus striatus) observed while sampling at Grammanik Tiger FSA (photo credit: N.Krampitz). ..................................................................................................................................................................................... 44 Figure 19. Mean fish biomass (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2003-2023. .............................................................................................................................................................................................................................. 45 Figure 20. Mean fish biomass (±SE) across St. Croix TCRMP monitoring sites from 2003-2023. .............................. 46 Figure 21. Average density (±SE) of the black spined sea urchin (Diadema antillarum) at 33 TCRMP monitoring sites in 2023. Note the log scale ..................................................................................................................................... 48 Figure 22. Average density (±SE) of Diadema antillarum at TCRMP sites from 2012-2023. ...................................... 48 Figure 23. An Acoustic Doppler Current Profiler (ADCP) installed on the reef to measure currents. ..................... 50 Figure 24. (top) The Buck Island, St. Croix position in the Buck Island Reef National Monument. (right) A representative photo (photo credit: VJ. Quetel). .............................................................................................................................. 53 Figure 25. Buck Island, St. Croix benthic temperatures (14 m depth). Data provided by the National Park Service (site BUIS_SFR). ............................................................................................................................................................................. 54 Figure 26. Buck Island, St. Croix benthic cover and coral health through time (mean ± SE). ................................... 56 Figure 27. The 2023 Buck Island, St. Croix fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................. 58 Figure 28. (top) The Buck Island Deep, St. Croix position in the Buck Island Reef National Monument. (right) A representative photo (photo credit: J. Quetel). ............................................................................................................................. 59 Figure 29. Buck Island Deep, St. Croix benthic temperatures (33 m depth). ..................................................................... 60 Figure 30. Stony Coral Tissue Loss Disease at Buck Island STX Deep, November 2021 (photo credit. K. Cobleigh). .......................................................................................................................................................................................................... 61 Figure 31. Buck Island Deep, St. Croix benthic cover and coral health through time (mean ± SE). ........................ 63 Figure 32. The 2023 Buck Island Deep, St. Croix fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................. 65 Figure 33. (top) Cane Bay location. (right) A representative photo of the reef (photo credit: J. Quetel). ............ 67 Figure 34. Cane Bay benthic temperatures (8 m depth) ............................................................................................................ 68 Figure 35. Cane Bay benthic cover and coral health through time (mean ± SE). ............................................................ 70 Figure 36. The 2023 Cane Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................................................. 72 INDEX ix Figure 37. (top) Cane Bay Deep location. (right) A representative photo of the reef at the monitoring site (photo credit: J. Quetel). ............................................................................................................................................................................. 73 Figure 38. Cane Bay Deep temperature (Top : 39 m depth, bottom left: 67m depth, bottom right: 100 m depth). ................................................................................................................................................................................................................ 74 Figure 39. Installation of temperature monitoring stations at Cane Bay at 67 m (left) and 100 m (right) on the wall (credit: Viktor Brandtneris). .................................................................................................................................................. 75 Figure 40. Cane Bay Deep benthic cover and coral health through time (mean ± SE). ................................................ 77 Figure 19. The 2023 Cane Bay Deep fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................. 79 Figure 42. (top) Castle location. (right) A representative photo of the reef (photo credit: L. V. Brandteneris). 80 Figure 43. Castle benthic temperatures (9 m depth). .................................................................................................................. 81 Figure 44. Time series through the 2023 bleaching event of a large Orbicella faveolata colony found at the beginning of one of the benthic transects at Castle (photo credit L. Henderson and B. Arrington) ......................... 82 Figure 45. Castle benthic cover and coral health through time (mean ± SE). .................................................................. 83 Figure 46. The 2023 Castle fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................................................. 85 Figure 47. (top) Eagle Ray location. (right) A representative photo of the reef (photo credit: L. M. Henderson). .............................................................................................................................................................................................................................. 87 Figure 48. Eagle Ray benthic temperature at 9 m depth ........................................................................................................... 88 Figure 49. Eagle Ray benthic cover and coral health through time (mean ± SE). .......................................................... 90 Figure 50. The 2023 Eagle Ray fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................................................. 92 Figure 51. (top) Great Pond location. (right) A representative photo of the reef (photo credit: L. M. Henderson). ..................................................................................................................................................................................................... 93 Figure 52. Great Pond benthic temperature (5 m depth). ......................................................................................................... 94 Figure 53. Great Pond benthic cover and coral health through time (mean ± SE). ........................................................ 96 Figure 54. The 2023 Great Pond fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. .............................................................................................................................. 98 INDEX x Figure 55. (top) Jacks Bay location. (right) A representative photo of the reef (photo credit: L. M. Henderson). .............................................................................................................................................................................................................................. 99 Figure 56. Jacks Bay benthic temperature at 12 m depth ...................................................................................................... 100 Figure 57. Jacks Bay benthic cover and coral health through time (mean ± SE). ........................................................ 102 Figure 58. The 2023 Jacks Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 104 Figure 59. Kings Corner. (top) Location. (right) A representative photo of the reef (photo credit: L. M. Henderson). .................................................................................................................................................................................................. 105 Figure 60. Kings Corner benthic temperature (17 m depth) ................................................................................................. 106 Figure 61. Kings Corner benthic cover and coral health through time (mean ± SE). ................................................. 108 Figure 62. The 2023 Kings Corner fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 110 Figure 63. Lang Bank EEMP. (top) Location. (right) A representative photo of the reef. ........................................ 111 Figure 64. Lang Bank EEMP benthic temperature (Top: 28 m depth, bottom left: 67m depth, bottom right: 100 m depth). ........................................................................................................................................................................................................ 112 Figure 65. Changing of thermistors at Lang Bank EEMP at 100 m (credit: Viktor Brandtneris). ......................... 113 Figure 66. Lang Bank EEMP benthic cover and coral health through time (mean ± SE). ........................................ 115 Figure 67. The 2023 Lang Bank EEMP fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 117 Figure 68. Lang Bank Red Hind FSA. (top) Location. (right) A representative photo of the reef in 2021. (photo: T. Smith) ......................................................................................................................................................................................................... 119 Figure 69. Lang Bank Hind current speed (left) and benthic temperature (right; 33 m depth). .......................... 120 Figure 70. Lang Bank Red Hind FSA benthic cover and coral health through time (mean ± SE). ........................ 122 Figure 71. The 2023 Lang Bank Red Hind FSA fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 124 Figure 72. Mutton Snapper. (top) Location. (right) A representative photo of the reef taken in 2017. (photo: L. Henderson) ................................................................................................................................................................................................... 125 Figure 73. Mutton Snapper benthic temperature record at 24 m (left) and 40 m depth (right). ......................... 126 Figure 74. Mutton Snapper benthic cover and coral health through time (mean ± SE). .......................................... 128 INDEX xi Figure 75. The 2023 Mutton Snapper fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 130 Figure 76. Salt River. (top) Location. (right) A representative photo of the reef (photo credit: L. Henderson). ........................................................................................................................................................................................................................... 131 Figure 77. Salt River West surface-benthic temperature record. Data provided by the NOAA ICON monitoring network and the Atlantic Oceanographic and Meteorological Laboratory (CRCP NCRMP Project number 7430). .............................................................................................................................................................................................................. 132 Figure 78. Salt River West benthic cover and coral health through time (mean ± SE). ............................................. 134 Figure 79. The 2023 Salt River West fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 136 Figure 80. Salt River Deep. (top) Location. (right) A representative photo of the reef (photo credit: L. Henderson). .................................................................................................................................................................................................. 137 Figure 81. Salt River Deep benthic temperature (Top left: 30 m depth, top right: 41 m depth, bottom left: 67 m depth, bottom right: 100 m depth). ................................................................................................................................................... 138 Figure 82. Installation of temperature monitoring stations at Salt River Deep at 100 m in the canyon (credit: Viktor Brandtneris). .................................................................................................................................................................................. 139 Figure 83. Salt River Deep benthic cover and coral health through time (mean ± SE). ............................................ 141 Figure 84. The 2023 Salt River Deep fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 143 Figure 85. Sprat Hole. (top) Location. (right) A representative photo of the reef (photo credit: L. M. Henderson). .................................................................................................................................................................................................. 145 Figure 86. Sprat Hole benthic temperature (7 m depth). ........................................................................................................ 146 Figure 87. Sprat Hole benthic cover and coral health through time (mean ± SE). ...................................................... 148 Figure 88. The Sprat Hole fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ...................................................................................................................................... 150 Figure 89. Coral Bay. (top) Location. (right) A representative photo of the reef. ....................................................... 152 Figure 90. Coral Bay benthic temperature (9 m depth) .......................................................................................................... 153 Figure 91. Coral Bay benthic cover and coral health through time (mean ± SE). ........................................................ 155 INDEX xii Figure 92. The 2023 Coral Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 157 Figure 93. Fish Bay. (top) Location. (right) A representative photo of the reef (photo credit: S. Kadison). .... 158 Figure 94. Fish Bay benthic temperature record (6 m depth). ............................................................................................. 159 Figure 95. Fish Bay benthic cover and coral health through time (mean ± SE). .......................................................... 161 Figure 96. The 2023 Fish Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 163 Figure 97. Meri Shoal. (top) Location. (right) A photo of the reef taken during the bleaching of 2023 (photo credit: N. Krampitz). ................................................................................................................................................................................. 164 Figure 98. Meri Shoal benthic temperature record (30 m depth). ...................................................................................... 165 Figure 99. Meri Shoal benthic cover and coral health through time (mean ± SE). ..................................................... 167 Figure 100. The 2023 Meri Shoal fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 169 Figure 101. Black Point. (top) Location. (right) A representative photo of the reef in 2019 (photo credit: V. Brandteneris). ............................................................................................................................................................................................. 171 Figure 102. Black point current speed and benthic temperature record (8 m depth). .............................................. 172 Figure 103. Black Point chlorophyll (left) and turbidity (right) record (16 m depth). .............................................. 173 Figure 104. Black Point benthic cover and coral health through time (mean ± SE). ................................................. 175 Figure 105. The 2023 Black Point fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 177 Figure 106. Botany Bay. (top) Location. (right) A representative photo of the reef. ................................................. 178 Figure 107. Botany Bay benthic temperature record (11 m depth). ................................................................................... 179 Figure 108. A large colony of pillar coral (Dendrogyra cylindrus) dislodge, toppled, and diseased after the 2009 swell event (Botany Bay, June 25, 2009). ............................................................................................................................. 179 Figure 109. Botany Bay benthic cover and coral health through time (mean ± SE). ................................................. 181 Figure 110. The 2023 Botany Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 183 INDEX xiii Figure 111. Brewers Bay. (top) Location. (right) A representative photo of the reef in 2024. (photo: S. Parr) ........................................................................................................................................................................................................................... 184 Figure 112. Brewers Bay benthic temperature record (8 m depth). .................................................................................. 185 Figure 113. Brewers Bay benthic cover and coral health through time (mean ± SE). ............................................... 187 Figure 114. The 2023 Brewers Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 189 Figure 115. Buck Island, St. Thomas. (top) Location. (right) A representative photo of the reef in 2024 (photo credit: T. Smith). ......................................................................................................................................................................................... 190 Figure 116. Buck Island, St. Thomas benthic temperature record (12 m depth). ........................................................ 191 Figure 117. Buck Island, St. Thomas benthic cover and coral health through time (mean ± SE). ........................ 193 Figure 118. A threatened Nassau grouper in an Antillean fish trap just of the Buck Island, St. Thomas TCRMP site. A second Nassau grouper was in another trap nearby. Aug. 12, 2008 (credit: T. Smith) ................................. 194 Figure 119. The 2023 Buck Island, St. Thomas fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 195 Figure 120. Coculus Rock. (top) Location. (right) A representative photo of the reef showing the aggregation of yellowfin parrotfish. ............................................................................................................................................................................ 196 Figure 121. Coculus Rock benthic temperature record (7 m depth). ................................................................................. 197 Figure 122. Coculus Rock benthic cover and coral health through time (mean ± SE). .............................................. 199 Figure 123. The 2023 Coculus Rock fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 201 Figure 124. College Shoal. (top) Location. (right) A representative photo of the reef in 2024 (photo: T. Smtih). ........................................................................................................................................................................................................................... 202 Figure 125. College Shoal benthic temperature record (29 m depth). .............................................................................. 203 Figure 126. College Shoal benthic cover and coral health through time (mean ±SE). ............................................... 205 Figure 127. The 2023 College Shoal fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 207 Figure 128. Flat Cay. (top) Location. (right) A representative photo of the reef in 2018. (photo: E. Kadison) ........................................................................................................................................................................................................................... 208 Figure 129. Flat Cay benthic current speed (left) and temperature record (right) (14 m depth). ....................... 209 INDEX xiv Figure 130. Flat Cay benthic cover and coral health through time (mean ± SE). ........................................................ 211 Figure 131. The 2023 Flat Cay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 213 Figure 132. Ginsburgs Fringe. (top) Location. (right) A representative photo of the reef showing whorled lettuce coral colonies up to 7m in width in 2018 (Photo: V. Brandtneris). ....................................................................... 214 Figure 133. Ginsburgs Fringe current speed (50 m depth) and benthic temperature (63 m depth). BT = bleaching threshold ; DHW = degree heating weeks. ................................................................................................................. 215 Figure 134. Ginsburg Fringe coral and benthic cover (±SE) over time. ............................................................................. 217 Figure 135. The Ginsburgs Fringe fish community in 2019 as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 219 Figure 136. Grammanik Tiger (top) Location. (right) A representative photo of the reef in 2019. (photo: V. Brandtneris) ................................................................................................................................................................................................. 220 Figure 137. Grammanik Tiger benthic currents speed (2005-2009) and temperature record (38 m depth). 221 Figure 138. Grammanik Tiger benthic cover and coral health through time (mean ± SE). .................................... 223 Figure 139. The 2023 Grammanik Tiger fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 225 Figure 140. Hind Bank (top) Location. (right) A representative photo of the reef in 2018 (photo: L. Henderson) ................................................................................................................................................................................................... 226 Figure 141. (top) Hind Bank benthic current speed (40m depth). (bottom) Benthic temperature record at 40 m depth. ......................................................................................................................................................................................................... 227 Figure 142. Hind Bank East benthic cover and coral health through time (mean ± SE). ......................................... 229 Figure 143. The 2023 Hind Bank East fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 231 Figure 144. Little St. James. (top) Location. (right) A representative photo of the reef with derelict fish trap ........................................................................................................................................................................................................................... 232 Figure 145. Little St. James benthic temperature record (19 m depth). ........................................................................... 233 Figure 146. Little St. James benthic cover and coral health through time (mean ± SE). .......................................... 235 INDEX xv Figure 147. The 2023 Little St. James fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 237 Figure 148. Magens Bay. (top) Location. (right) A representative photo of the reef. ............................................... 238 Figure 149. Magens Bay current speed and benthic temperature record (9 m depth). ............................................ 239 Figure 150. Magens Bay chlorophyll (left) and turbidity (right) record (16 m depth). ............................................ 240 Figure 151. Magens Bay benthic cover and coral health through time (mean ± SE). ................................................ 242 Figure 152. The 2023 Magens Bay fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 244 Figure 153. Savana. (top) Location. (right) A representative photo of the reef showing large colonies of Orbicella faveolata (Nov. 17, 2015). .................................................................................................................................................. 245 Figure 154. Savana benthic temperature record (10 m depth). .......................................................................................... 246 Figure 155. Savana Island benthic cover and coral health through time (mean ± SE). ............................................ 248 Figure 156. The 2023 Savana Island fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 250 Figure 157. Seahorse Cottage Shoal. (top) Location. (right) A representative photo of the reef. ........................ 251 Figure 158. Seahorse benthic temperature record (21 m depth). ....................................................................................... 252 Figure 159. Seahorse Cottage Shoal benthic cover and coral health through time (mean ± SE). ........................ 254 Figure 160. The 2023 Seahorse Cottage Shoal fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 256 Figure 161. South Capella. (top) Location. (right) Representative photo of the reef (photo: V. Brandtneris).257 Figure 162. South Capella benthic temperature record (Top left: 24 m depth, top right: 35 m depth). ............ 258 Figure 163. South Capella benthic cover and coral health through time (mean ± SE). ............................................. 260 Figure 164. The 2023 South Capella fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................... 262 Figure 165. South Water. (top) Location. (right) A representative photo of the reef (Photo: J. Quetel). .......... 263 Figure 166. South Water benthic temperature record (24 m depth). ............................................................................... 264 Figure 167. South Water benthic cover and coral health through time (mean ± SE). ............................................... 266 INDEX xvi Figure 168. The South Water fish community as (A-D) average biomass per trophic group with the most common species shown in order on the x-axis, (E) species richness, and (F) relative community composition by total biomass. Note that biomass is a log scale. ........................................................................................................................... 268 INDEX xvii Index of Tables Table 1. TCRMP site reef complex type, location coordinates (decimal degrees; WGS 1984), and depths. ........... 22 Table 2. TCRMP sampling dates for fish, urchin, benthic cover, and coral health at each site. .................................. 23 Table 3. The 2023 species richness for belt transects and roving diver surveys (RDS). ................................................. 40 MISSION STATEMENT 1 To provide critical information on the status and threats to all Virgin Islands coral reef ecosystems in order to increase management effectiveness and improve basic and applied coral reef research OBJECTIVES • Monitor the status and trajectories of coral reefs across a variety of habitats and threats, including land-based sources of pollution & thermal stress • Link changes in coral reef health with specific stressors, indicating specific management interventions most effective for preserving reefs • Integrate assessments of understudied mesophotic coral reef ecosystems and threatened species in the USVI • Provide data, outputs, and advice to stakeholders and create a nexus of information for reef research OUR VISION To provide critical information on the status and threats to all the U.S. Virgin Island’s coral reef ecosystems to increase management effectiveness and improve basic and applied coral reef research EXECUTIVE SUMMARY 2 Executive Summary Coral reefs in the Caribbean are at a crossroads, facing the possibility of further dramatic decline. Management decisions made today will affect the goods and services that coral reefs provide for decades to come. The government of the United States Virgin Islands (USVI), in coordination with the NOAA Coral Reef Conservation Program and the University of the Virgin Islands, implemented the Territorial Coral Reef Monitoring Program (TCRMP). The TCRMP has established baseline conditions and temporal trends of coral reefs and fish populations in the USVI and has identified threats that influence future reef health and development. A major focus of the TCRMP is to provide information that can lead to more effective management strategies that balance the immediate needs of the Virgin Island’s population with the preservation and sustainability of coral reefs and the renewable goods and services they provide. The intent of this report is to distill monitoring data into actionable information that can guide management decisions and inform the public and policy-makers about areas that need further effort. This executive summary presents information on threats to USVI reefs that require management intervention/action as well as positive signs that can inform our understanding of sustainability. CORAL REEFS OF THE VIRGIN ISLANDS: MANGEMENT ACTIONS NEEDED The TCRMP data has identified threats to USVI coral reef ecosystems that need increased management attention if reef corals are to persist in a condition that is equal to or better than current conditions. Coral Reef Bleaching. High thermal stress caused by climate change is currently the greatest threat to USVI coral reef ecosystems. The 2005 coral bleaching event caused the largest loss of coral in the documented history of the USVI, with a 50% decline in coral cover in shallow waters less than 25m/85’ deep (Smith et al. 2013b; Smith et al. 2016a). EXECUTIVE SUMMARY 3 This event surpassed all known modern impacts from physical damage (storms and anchoring), ecosystem changes (fishing and disease), and pollution (terrestrial sediments and toxins). This thermal disturbance was compounded by record heat stress in the fall of 2023 and 2024, with widespread bleaching and community effects that are only now being investigated. Please see `Research Highlights` for more detailed information on this bleaching event. While local management actions cannot remove impacts to reefs from global warming, reefs that are otherwise less stressed by land-based sources of pollution, fishing, and/or physical damage are known to recover more quickly from bleaching. Hence, local management actions that promote seascape-wide coral reef health offer the best strategy for sustainable reefs. We can also identify areas that are naturally more resistant to thermal stress and offer these areas further protection, since they offer insurance against the worst possible future outcomes for USVI reefs. Figure 1. Partially bleached and recovering colony of Siderastrea siderea at Flat Cay, St. Thomas (Nov. 12, 2005). EXECUTIVE SUMMARY 4 Overfishing. There are clear indications that reefs of the USVI are suffering the effects of overexploitation of reef resources. The entire district of St. Croix has an extremely low abundance of commercially important grouper species, including the threatened Nassau grouper (Kadison et al. 2017). In St. John and St. Thomas, many common species have completely or nearly disappeared from nearshore waters in the last 30 years. For example, a study conducted by Rogers et al. (1982) on the southwest coast of St. Thomas found a variety of species that are no longer encountered or are rare, including the black, Nassau, yellowfin, and tiger groupers, as well as the federally protected parrotfish species: blue, midnight, and rainbow. Rebuilding these fish stocks will require knowledge of comprehensive life-history information for target species, a willingness to find strategies to rebuild stocks, and partnerships between commercial and recreational fishers, community stakeholders, and managers. Signs of an increasing recruiting and spawning population of Nassau groupers in the northern USVI and more frequent sightings at TCRMP sites in St. Croix suggests that management actions, including no-take restrictions and protection of spawning aggregation sites, can have tangible, positive effects (Kadison et al. 2010). In addition, recent work under the Deep Coral Reef Monitoring Program, an extension of the spatially randomized National Coral Reef Monitoring Program in depths between 30-50 m (100-165 feet), is finding higher abundances of commercially important species that are rare in shallow waters (Grove et al. 2024; Heidmann et al. 2024). Therefore, for many species viable populations may still exist for rebuilding stocks. Land-Based Source of Pollution. The steep hillsides of the USVI are natural conduits for run-off during heavy rain events and in many instances, there is little interception of materials before they reach the sea and impact coral reefs. When tropical soils are naturally disturbed or altered through human activity, they can erode and release fine- grained silt and clay particles. In the USVI, these fine-grained particles are quickly transported to coral reefs where they can block sunlight, directly smother corals, or increase the growth of organisms that compete with corals for space. There is evidence EXECUTIVE SUMMARY 5 from the TCRMP that terrestrial sediments are having large negative impacts on nearshore coral reefs by increasing mortality of ecologically important corals (Ennis et al. 2016; Henderson et al. in prep.). CORAL REEFS OF THE VIRGIN ISLANDS: POSITIVE SIGNS Despite the incredible declines in reef health witnessed since the inception of the TCRMP in 2001, there are many positive signs for the USVI that should be highlighted. These successes offer lessons that can be applied to troubled reefs and may indicate refuge areas where we might “double-down” on current management strategies. Reef Refuges. The USVI is blessed with extensive areas of deep bank and slope reefs that may be buffered from the direct impacts of local pressures (Smith et al. 2019a, b). The mesophotic (pronounced: me-zo-photik; meaning; “middle-light”) reefs of the USVI are the best developed in the Caribbean from what is currently known. Mesophotic Coral Ecosystem (MCE) reefs with high populations of star corals (Orbicella spp.), which are listed as threatened on the United States Endangered Species List (NOAA 2014), form extensive tracts on the south shelf of St. John and St. Thomas, from the British Virgin Islands to Vieques, Puerto Rico. Well-formed, but patchier mesophotic boulder coral reefs also form on the Lang Bank of St. Croix and the northern Puerto Rican Shelf. The lower MCE consists mostly of lettuce corals (primarily Agaricia undata) and form a semi- continuous ring on steep slopes and walls at depths between 50-70m. These reefs are isolated from some, but not all, local impacts but may be susceptible to global climate change (see below). In federal waters some of these areas are wholly or partly protected from fishing of ecologically important species that help maintain reef health. These include the Red Hind Marine Conservation District (est. 1999), the Grammanik Bank Seasonally Closed Area (est. 2005), and the Lang Bank Red Hind Seasonally Closed Area (est. 1993). However, extensively developed mesophotic reef in unprotected territorial waters also exist near the island of French Cap and Sail Rock in St. Thomas. It is important that these EXECUTIVE SUMMARY 6 areas are identified, their threats assessed, and they are incorporated into the territorial and federal management planning process. Rebounding Fisheries Species. There are positive signs of recovery for certain fish species in some areas. A red hind aggregation in the Red Hind Marine Conservation District (MCD) has dramatically rebounded (Nemeth 2005) and at the Grammanik Bank, a multi- species fish spawning aggregation site, there have been increasing numbers of Nassau grouper during annual spawning (Kadison et al. 2010; Jackson et al. 2014). About 875 individuals were seen in 2023-2024 (R. Nemeth, unpub. obs), contrasting the ~100 individuals seen spawning only a decade previously. Recruitment pulses of juvenile Nassau grouper in nearshore environments have also been noted in St. Thomas and St. John (R. Nemeth, unpub. data). Other territorial and federal closed areas in St. Croix, St. John, and St. Thomas are more recently established and thus may not show effects for several years. It has also been recently documented in the National Coral Reef Monitoring Program that larger and more numerous commercially important fish populations are found in deeper areas south of St. Thomas-St. John (Grove et al. 2024, Heidmann et al. 2024). For species that are completely protected from fishing (Nassau grouper and blue, midnight, and rainbow parrotfish), educational campaigns for recreational and commercial fisherman are critical, as awareness of regulations among the USVI residents appears to be lacking (Authors, unpub. obs.). Land-based source of pollution. While development of steep island slopes has continued despite current regulations intended to prevent sediments from entering nearshore waters, research has identified key targets for restoration and some effective habitat restoration best-management practices. Results from TCRMP research suggest that there are certain levels of silt-laden terrestrial run-off that are damaging to corals, providing a target for reductions of sediment in the marine environment (Henderson et al. in prep.). Unpaved road segments have been implicated as the worst culprits in the production of sediment-laden run-off (Ramos-Scharrón and MacDonald 2007a, b) and this provides a clear target for where management can be most effectively applied. Restoration of EXECUTIVE SUMMARY 7 watersheds has shown that implementation of best-management practices and control structures can be effective in reducing sedimentation. For example, the American Recovery and Reinvestment Act project “USVI Coastal Habitat Restoration Through Watershed Stabilization” showed promising results (Virgin Islands Resource Conservation and Development Council; P.I. M. Taylor). _____________________________________________________________________________________________________ This report presents results of the 23rd year of monitoring on reefs surrounding St. Croix, St. John, and St. Thomas, and includes surveys from annual sampling (2001- 2023) as well as an additional post-bleaching benthic sampling that occurred in the early spring 2024. Monitoring sites were distributed across the insular platform in depths from 5 to 63 m (16 – 220’) to capture the diversity of reef types present in the Virgin Islands. Long-term data is presented from 34 sites. While not exhaustive, the TCRMP is generally representative of the geographic areas and variety of reef types in the USVI. Digital video and diver surveys were used to quantify benthic cover and coral health at 15 permanent sites surrounding the island of St. Croix and 19 permanent sites on the Puerto Rican Shelf surrounding the island of St. John and St. Thomas. In addition, at 33 of these sites, sea urchin density and fish community structure were evaluated. The TCRMP website describes the program and houses updated data https://www.vitcrmp.org Data can also be requested directly from the research team by contacting Erin Hollander at erin.hollander@uvi.edu INTRODUCTION 8 Impacts, Scope, and Comparisons of the 2023 Coral Bleaching Event In 2023, sea surface temperatures in the U.S. Virgin Islands reached unprecedented highs, inducing a mass coral bleaching event—the fourth to occur in the past 20 years (Fig. 2). Sea surface temperatures in the USVI have been increasing at a rate of about 0.2°C per decade since the 1980’s (Fig. 3), increasing the incidence of coral thermal stress, measured as Degree Heating Weeks (DHW; Fig. 3). Major bleaching events since TCRMP monitoring began have occurred in 2005 (DHW=15.5), 2010 (DHW=9.8), and 2019 (DHW=8.9). In the fall of 2023, DHW peaked at 18.7, coinciding with observations of widespread bleaching and coral mortality, in both shallow and mesophotic environments. The waters were warmest during the months of September and October, when sea surface temperatures consistently stayed above 30.0˚C. note Figure 2. TCRMP diver surveys bleached corals during the peak of thermal stress at the Meri Shoal TCRMP monitoring site, December 7th, 2023 (photo credit: N. Krampitz) INTRODUCTION 9 Figure 3. 1982 – 2023 sea surface temperature (left axis ,blue line), left vertical axis and degree heating weeks (right axis, red line) for the USVI. The black line is a linear fit of the sea surface temperature showing a 0.024˚C increase in temperature per year (y = 0.0237/year * x - 26.75). Degree heating weeks (DHW) are calculated as the 12-week rolling sum of temperatures exceeding 1°C over the monthly maximum mean temperature, which is estimated at 28.5°C for the USVI (NOAA 2006). DHW values above 4 are associated with the onset of bleaching, and above 8 with the onset of mass bleaching and coral mortality. (Optimum Interpolation Sea Surface Data, OISST, from https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html, accessed April 17, 2025 by Lauren Olinger Ph.D.) Despite higher heat stress in 2023 compared to the 2005 bleaching event, it appeared that the bleaching response of corals in TCRMP locations was slightly stronger in 2005— both in bleaching extent and bleaching prevalence (Fig. 4). It should be noted, however, that not all sites were sampled during the peak of heat stress every year, which may underestimate bleaching responses for a given site. Furthermore, many of the deeper sites (e.g., Salt River Deep, Buck Island Deep) were not established until after 2005. INTRODUCTION 10 In 2005, bleaching prevalence averaged 70±6% across all sites with a dramatic extent (mean 82% of colonies’ surface affected). In 2019, bleaching prevalence was lower (46±3%) as well as extent (36±4%). In this most recent year, bleaching prevalence was estimated to be near 71.5±2.5% across TCRMP locations with over 70% of each colony Figure 4. Mean coral bleaching prevalence and extent at each TCRMP site in 2005, 2019, and 2023. Bleaching prevalence is the proportion of the community showing some level of stark white bleaching. Bleaching extent is the mean proportion of the colony area affected by stark white bleaching. Sites are organized by increasing depth. INTRODUCTION 11 affected on average. All sites in 2023 were sampled between October 10th and December 12th, with peak heating stress estimated to be mid-October. Species most affected by the bleaching in terms of prevalence included Agaricia spp. (83%), Orbicella spp. (70%), Millepora spp. (68%), and branching Porites spp. (65%). In mid-February 2024, a post-bleaching sampling began in response to the observed bleaching event during annual TCRMP sampling. Although bleaching prevalence on the reef had largely abated by early spring (~5% bleached colonies), paling presence was notably high (~30%), especially on deeper mesophotic reefs. Correspondingly, these deeper reefs also experienced slightly higher bleaching prevalence during the fall than their shallow water counterparts. Recent partial mortality was highly prevalent in post-bleaching surveys (~20% of corals affected) across all depths, and disease was occasionally noted, most frequently on Orbicella colonies at deeper depths. Changes in coral coverage during and after the bleaching event varied by site (Fig. 5), but there was an overall significant decline in relative coral coverage, with a mean relative loss of 21.8±4.3% in less than 6 months. Deeper sites, Orbicella-dominated sites, and those with higher initial coral coverage appeared to be most affected by coral mortality. Sites with higher bleaching prevalence experienced significantly greater declines in coral cover, indicating a strong negative relationship between bleaching intensity and coral cover change (linear regression; p < 0.01). A significant relationship was also found between the projected accumulated DHW at individual sites and the observed extent of bleaching (p = 0.02). These results indicate for the 2023 bleaching event, the intensity (i.e., extent) of bleaching was highly correlated with DHW, but the impact of bleaching, notably measured by associated losses in coral coverage, was largely driven by prevalence of bleaching at a site. These findings underscore the importance of not only quantifying bleaching on a site level (prevalence), but also on a colony level (extent) and INTRODUCTION 12 intensity (paling vs. bleaching) level to fully understand how corals are reacting to rising sea surface temperatures. Figure 5. Mean coral cover at each TCRMP location during peak bleaching in the fall of 2023 and post-bleaching sampling in the fall of 2024. Loss in coverage over this 4-to-6-month period was significant (paired t-test: p<0.0001). INTRODUCTION 13 Introduction The U.S. Virgin Islands consist of three large islands, St. Thomas, St. John and St. Croix, and numerous smaller islands surrounded by a diverse, tropical marine environment that includes coral reefs, seagrass beds, and mangrove forests (Fig. 7). The islands of St. Thomas and St. John lie on the Puerto Rican Shelf, an extensive shallow water platform that connects them to Puerto Rico to the west and the British Virgin Islands to the east. St. Croix lies on an isolated platform sixty-five kilometers to the south of St. Thomas and St. John and separated by the 4000m deep Anegada Passage and the Virgin Islands Trough. This forms an effective barrier to the migration of adult coral reef fishes and invertebrates. The coral reefs of the Virgin Islands represent a wide range of characteristic coral reef habitats of the Caribbean, including patch reefs, fringing reefs, barrier reefs, shelf reefs, and extensive bank and slope mesophotic coral reef ecosystems. The area of a star coral bank mesophotic reef complex south of St. Thomas to Vieques covers more area than all the shallow water coral reefs of the USVI combined (Smith et. al 2019a). The economy of the US Virgin Islands is reliant to a large extent on maintenance of vibrant marine ecosystems. Tourism drives the economy of the Virgin Islands, which are famous for white sand beaches that give way to clean, clear marine waters. The diverse marine life of the coral reefs and other habitats attract thousands of snorkelers and scuba divers each year. Sport fishing on charter boats and private vessels also makes an important contribution to the economy. In addition, the coral reefs and other habitats in the Virgin Islands are essential to the lives of hundreds of thousands of species including economically important whelk, queen conch, spiny lobster, snapper, and grouper. Over three hundred full-time or part-time commercial fishermen work in territorial and federal waters surrounding all three islands (Tobias 1997). In tough economic times and after natural disasters, fishing is an important means of supplemental income or extra protein for many people. INTRODUCTION 14 Over the last few decades, major hurricanes, coral disease outbreaks, mass coral reef bleaching, and invasive species introductions have caused extensive coral mortality to the coral reefs surrounding the Virgin Islands (Gladfelter 1982; Edmunds and Witman 1991; Rogers et al. 1991; Rothenberger et al. 2008; Woody et al. 2008; Miller et al. 2009; Smith et al. 2013b; Brandt et al. 2021). Recovery from these disturbances is hindered by a multitude of human impacts that affect coral reefs, such as overfishing of ecologically important species, physical damage to reef structure, and pollution (Hatcher 1984; Pastorok and Bilyard 1985; Rogers and Garrison 2001; Mumby 2006; Mumby et al. 2006; Mumby and Harborne 2010). Moreover, rapid development of steep island slopes has dramatically increased soil erosion and sedimentation into nearshore waters (Brooks et al. 2007; Gray et al. 2008; Smith et al. 2008), particularly below unpaved road surfaces (Anderson and Macdonald 1998; Ramos-Scharrón and MacDonald 2007a). Chronic sedimentation affects the abundance and diversity of corals and other reef organisms, increases coral stress and susceptibility to diseases and bleaching, and reduces the ability of corals and other reef organisms to recover and regenerate after natural disturbances such as hurricanes (Acevedo and Morelock 1988; Rogers 1990; Nemeth and Sladeck Nowlis 2001; Fabricius 2005; Sabine et al. 2015; Ennis et al. 2016). The first sightings of the invasive Indo-Pacific lionfish (Pterois volitans) occurred in the US Virgin Islands in 2009. This predator can dramatically alter coral reef fish community structure (Cote and Maljkovic 2010) and these alterations may have additional, indirect impacts on benthic communities (Albins and Hixon 2011). In addition, the aggressive and possibly introduced red alga Ramicrusta textilis has increased in abundance at many locations and is killing coral tissue through competitive overgrowth (Bramanti et al. 2017; Edmunds et al. 2019; Hollister et al. 2021; Williams and Edmunds 2021). Stony Coral Tissue Loss Disease (SCTLD), first observed at the Flat Cay monitoring location in early 2019, has led to widespread coral mortality and diversity losses throughout the Virgin Islands over the last several years (Brandt et al. 2021). In addition, losses of the black spined sea urchin to INTRODUCTION 15 an epizootic scutiociliate outbreak in 2022 have greatly reduced the already impacted populations of this key Caribbean herbivore (Hylkema et al. 2023; Hewson et al. 2023). High thermal stress and coral bleaching events affected the northeastern Caribbean in 2005, 2010, 2012, 2019, and 2023. Prior to 2023, the most severe high sea surface temperature (SST) event occurred in 2005. Degree Heating Weeks (DHW) for this event peaked at 15.4 (NOAA Coral Reef Watch 2024; 5km satellite product) and was associated with severe coral bleaching and mortality (Miller et al. 2009). In the fall of 2023, DHW reached an all-time maximum of 18.7 (NOAA Coral Reef Watch 2024; 5km satellite product), coinciding with observations of wide-spread bleaching and coral mortality in shallow and mesophotic environments. (Authors, unpub. obs.) Recent research developed bleaching threshold temperatures for 24 of the 34 TCRMP monitoring sites dominated by star corals of the genus Orbicella (Smith et al. 2016a). This study concluded that mesophotic reefs of the USVI are unlikely to be long-term climate change refugia because they are not immune to high temperature thermal stress. This is further evidenced by the observed widespread (>45% of corals) bleaching that occurred at all mesophotic TCRMP sites in this most recent survey year (2023). Earlier events and the species-specific responses of Caribbean corals are summarized in Smith et al. (2013, b) for shallow corals and Smith et al. (2016, a) for shallow and mesophotic corals. Most research around the Virgin Islands has focused on fringing reefs (5 – 30 m depth) located along the shoreline of the three main islands, St. Thomas, St. John, and St. Croix. In contrast, very little information exists for offshore and deeper reef systems, which can be quite extensive. These other reef systems include mid-shelf reefs (5 – 30 m depth) located 2 to 10 km from the shore of the main islands and mesophotic reefs (>30 m depth) located from 0.5 to 15 km offshore along the edge of the insular platform (Armstrong et al. 2002; Armstrong et al. 2006; Armstrong 2007; Menza et al. 2007; Menza et al. 2008; Nemeth et al. 2008; Smith et al. 2010b; Smith et al. 2016b). Distance from shore may be a factor in the historical degeneration of coral reef systems in the INTRODUCTION 16 Virgin Islands (Herzlieb et al. 2005; Calnan et al. 2008; Smith et al. 2008; Sabine et al. 2015; Ennis et al. 2016). A systematic approach to investigating these cross-shelf coral reef systems allows us to evaluate the variable impacts and synergistic effects of natural impacts and human-induced stress that influence the decline or recovery of Caribbean coral reef systems. The first two years of this project (2001 and 2002) concentrated on the fringing reefs surrounding St. Croix. In 2003, monitoring continued at St. Croix reefs and began at reef systems distributed across the insular platform surrounding St. Thomas. In 2004-2006 monitoring continued at reefs surrounding both islands, with additional reefs surrounding St. Thomas added in 2004, 2005, and 2011. Mesophotic coral reef monitoring sites were added to St. Croix during the 2008, 2009, and 2017 monitoring. In 2011, the TCRMP also expanded to include sites established under separate funding that are continued in the core TCRMP monitoring activities funded by USVI DPNR and NOAA CRCP. OBJECTIVES FOR MONITORING CORAL REEFS Effective management is necessary to maintain the resources in the territorial and federal waters of the Virgin Islands in an ecologically and economically sustainable manner. Monitoring programs are essential for successful management because they provide managers with fundamental information with which to make and reinforce decisions. Standards for resource protection can be measured by comparison to baseline data established by monitoring. Monitoring also provides the means to assess the status and trends of ecological resources, allowing managers to determine the effectiveness of current management and to develop effective management plans for the future. The Territorial Coral Reef Monitoring Program monitors the condition of coral reefs throughout the U.S. Virgin Islands and provides key information to better manage these ecosystems. The TCRMP is complimentary to the National Coral Reef Monitoring Program (NCRMP) that started in 2013 and is co-coordinated in the USVI by the University of the Virgin Islands. TCRMP focuses on fixed sites and repeatedly samples the same corals to INTRODUCTION 17 generate the most in-depth metrics of change over time while NCRMP uses a stratified- random sampling design to spread out samples and gain an understanding of change through time, with predictions that can be applied spatially. NCRMP does not currently sample reefs below 30m, and therefore misses the dominant habitat in the northern USVI. The Deep Coral Reef Monitoring Program (DCRMP) was instituted in 2019 to sample reef fishes and basic benthic attributes in depths of 30-50 m on hardbottom areas south of St. Thomas and St. John (Grove et al. 2024; Heidmann et al. 2024). However, this program has no long-term sustained funding and sampling ended in 2022. This report presents monitoring results from 2001-2023 in St. Croix and from 2003-2023 in St. Thomas and St. John, as well results from a benthic-only post bleaching sampling that occurred at all sites in the spring of 2024. Figure 6. A TCRMP research diver (S. Heidmann) on closed circuit rebreather records a roving fish survey at the Salt River Deep wall site, 30m/100’ depth (April 9, 2020; credit: S. Meiling). INTRODUCTION 18 Figure 7. Locations of Territorial Coral Reef Monitoring Sites in the US Virgin Islands. Boundaries indicate federal and territorial marine protected areas. METHODS 19 Methods BENTHIC ASSESSMENTS The University of the Virgin Islands determined the benthic composition at 34 long-term monitoring sites between 2001 and 2024 (Table 1; Table 2). All data is now available at the TCRMP website and updated annually after quality control: https://www.vitcrmp.org Around St. Croix the following 15 sites were assessed: Buck Island-St. Croix, Buck Island Deep, Cane Bay, Cane Bay Deep, Castle, Eagle Ray, Great Pond, Jacks/Isaacs Bay, Kings Corner, Lang Bank East End Marine Park (Lang EEMP), Lang Bank Red Hind Fish Spawning Aggregation (Lang Hind), Mutton Snapper, Salt River, Salt River Deep, and Sprat Hole. Four of these sites are within the St. Croix East End Marine Park boundary (Castle, Great Pond, Jacks Bay, Lang EEMP), two sites are in a territorially managed area associated with Salt River (Salt River West and Salt River Deep), Buck Island-St. Croix and Buck Island Deep are within National Park Service/National Monument boundaries, two sites are within federal fisheries marine protected areas (Lang Hind, Mutton Snapper), and five sites can be considered mesophotic coral reefs (Buck Island Deep, Cane Bay Deep, Lang Bank EEMP, Lang Hind, Salt River Deep; sensu Ginsburg 2007) . Around St. John/St. Thomas the following 19 sites were assessed: Black Point, Botany Bay, Brewers Bay, Buck Island-St. Thomas, Coculus Rock, College Shoal East, Coral Bay, Fish Bay, Flat Cay, Ginsburgs Fringe, Grammanik Tiger FSA, Hind Bank FSA, Little St. James, Magens Bay, Savana Island, Seahorse Cottage Shoal, Meri Shoal, South Capella, and South Water Island. One site is the within the St. Thomas East End Reserve (Coculus Rock), four sites are within federal fisheries marine protected areas (College Shoal, Ginsburgs Fringe, Grammanik Tiger, Hind Bank), and five sites can be considered mesophotic coral reefs (College Shoal, Ginsburgs Fringe, Grammanik Tiger, Hind Bank, METHODS 20 Meri Shoal). Because of its deep depth, Ginsburgs Fringe at 60-66m was only sampled for benthic cover and occasional fish surveys. Benthic Cover. At each site benthic cover and coral health surveys were conducted along six 10 m long permanent transects marked with steel or brass rods. Video sampling consisted of one diver traversing each transect videotaping the benthic cover using a standard definition digital video camera (prior to 2007) or a high-definition digital camera (after 2007). TCRMP has attempted to continually upgrade video equipment through time to maintain the highest quality imagery possible for benthic analysis. The diver swam at a uniform speed, pointing the camera down and keeping the lens approximately 0.4 m above the substrate at all times. A guide wand or dropper weight attached to the camera housing was used to help the diver maintain the camera a constant distance above the reef. After taping, approximately 20 - 50 non-overlapping images per transect were captured and saved as JPEG files (Fig. 8). Captured images represented an area of reef approximately 0.31 m2 (0.64 m x 0.48 m). Coral Point Count with Excel Extension software (Kohler and Gil 2006; prior to 2019) or R Studio (RStudio Team 2015; 2019 onward) was used to superimpose randomly located dots on each image. The number of points varied with the evolution of the video camera systems and was 10 points from 2001-2011, 15 points from 2012-2013, and 20 points from 2014 onwards. The substrate type located under each of the dots was then identified to the most descriptive level possible and entered into a database. Where multiple benthic cover categories fell under a single point, for example macroalgae over bedrock, the upper benthic category was assessed. For each transect, the percent cover of coral, epilithic algae, macroalgae, sponges, gorgonians, and sand/sediment were calculated by dividing the number of random dots falling on that substrate type by the total number of dots for that transect. Epilithic algae (sensu Hatcher and Larkum 1983) are diminutive turfs and filamentous algae without thallus structure that cover all rock surfaces of coral reefs not occupied by larger epibenthic organisms. METHODS 21 Figure 8. A screen grab of benthic video used for the determination of percent cover of coral reef organisms and non-living substrate. METHODS 22 Table 1. TCRMP site reef complex type, location coordinates (decimal degrees; WGS 1984), and depths. Island Site Reef Complex Lat Long Depth (m) St. Croix Buck Island-St. Croix Offshore-Shallow 17.78500 -64.60917 15 Buck Island Deep-St. Croix Offshore-MCE 17.80659 -64.59935 33 Cane Bay Nearshore 17.77388 -64.81350 10 Cane Bay Deep Offshore-MCE 17.77661 -64.81522 38 Castle Offshore-Shallow 17.76278 -64.59743 7 Eagle Ray Offshore-Shallow 17.76150 -64.69880 10 Great Pond Nearshore 17.71097 -64.65221 6 Jacks Bay Nearshore 17.74337 -64.57160 14 Kings Corner Nearshore 17.69116 -64.90008 17 Lang Bank EEMP Offshore-MCE 17.72145 -64.54706 27 Lang Bank Red Hind FSA Offshore-MCE 17.82372 -64.44943 33 Mutton Snapper FSA Offshore-Shallow 17.63660 -64.86240 24 Salt River Deep Offshore-MCE 17.78523 -64.75917 30 Salt River West Nearshore 17.78530 -64.75940 11 Sprat Hole Nearshore 17.73400 -64.89540 8 St. John Coral Bay Nearshore 18.33797 -64.70402 9 Fish Bay Nearshore 18.31417 -64.76408 6 Meri Shoal Offshore-MCE 18.24433 -64.75832 30 St. Thomas Black Point Nearshore 18.34450 -64.98595 9 Botany Bay Nearshore 18.35845 -65.03330 8 Brewers Bay Nearshore 18.34403 -64.98435 7 Buck Island-St. Thomas Offshore-Shallow 18.27883 -64.89833 14 Coculus Rock Nearshore 18.31257 -64.86058 7 College Shoal East Offshore-MCE 18.18568 -65.07677 30 Flat Cay Offshore-Shallow 18.31822 -64.99104 12 Ginsburgs Fringe Offshore-MCE 18.18770 -64.95998 63 Grammanik Tiger FSA Offshore-MCE 18.18901 -64.95630 38 Hind Bank East FSA Offshore-MCE 18.20217 -65.00158 39 Magens Bay Nearshore 18.37425 -64.93438 7 Savana Offshore-Shallow 18.34064 -65.08205 9 Seahorse Cottage Shoal Offshore-Shallow 18.29467 -64.86750 20 South Capella Offshore-Shallow 18.26267 -64.87237 20 South Water Offshore-Shallow 18.28068 -64.94592 20 Little St James Offshore-Shallow 18.29459 -64.83238 17 METHODS 23 Table 2. TCRMP sampling dates for fish, urchin, benthic cover, and coral health at each site. Where there are two dates an asterisk (*) indicates the full fish survey date for St. Thomas-St. John and clean up surveys for St. Croix (finished during post-bleaching surveys in 2024). Only benthic surveys were completed at Ginsburgs Fringe. Only benthic and health surveys were completed during the post-bleaching sampling season in spring of 2024. Island Site Annual Survey Sample Date (2023) Post-Bleaching Sample Date (2024) St. Croix Buck Island STX 11/9/23 3/13/24 Buck Island STX Deep 11/9/23, 3/11/24* 3/11/24 Cane Bay 11/12/23 3/13/24 Cane Bay Deep 11/12/24, 3/13/24* 3/13/24 Castle 11/13/23 3/11/24 Eagle Ray 11/11/23 3/13/24 Great Pond 11/14/23 3/12/24 Jacks Bay 11/14/23 3/14/24 Kings Corner 11/15/23 3/15/24 Lang Bank EEMP 11/14/23, 3/16/24* 3/16/24 Lang Bank Red Hind FSA 11/13/23 3/12/24 Mutton Snapper FSA 11/10/23, 3/15/24* 3/15/24 Salt River Deep 11/11/23 3/14/24 Salt River West 11/11/23 3/14/24 Sprat Hole 11/12/23 3/14/24 St. John Coral Bay 8/25/23*, 10/13/23 2/16/24 Fish Bay 8/25/23*, 10/13/23 2/16/25 Meri Shoal 9/5/23*, 12/7/23 4/22/24 St. Thomas Black Point 8/30/23*, 10/17/23 2/15/24 Botany Bay 9/27/23*, 10/12/23 4/17/24 Brewers Bay 8/30/23*, 10/17/23 4/11/24 Buck Island STT 9/1/23*, 10/19/23 4/2/24 Coculus Rock 8/25/23*, 10/13/23 4/2/24 College Shoal East 9/22/23*, 12/6/23 5/14/24 Flat Cay 8/30/23*, 10/17/23 2/15/24 Ginsburgs Fringe 10/26/23 5/22/24 Grammanik Tiger FSA 9/7/23*, 12/5/23 4/8/24 Hind Bank East FSA 9/6/23*, 12/6/23 5/14/24 Magens Bay 9/27/23*, 10/12/23 4/17/24 Savana 9/27/23*, 10/30/23 4/11/24 Seahorse Cottage Shoal 8/31/23*, 10/30/23 3/7/24 South Capella 8/31/23*, 10/23/23 4/22/24 South Water 9/1/23*, 10/23/23 4/26/24 Little St James 9/25/23*, 10/19/23 4/26/24 METHODS 24 Coral Health. Coral health assessments followed methodologies outlined in Calnan et al. 2008, Smith et al. 2008, and Smith et al. 2013, and are briefly described here. All coral colonies located directly under the transect lines were assessed in situ for signs of mortality and disease following a modified Atlantic and Gulf Rapid Reef Assessment protocol (Kramer et al. 2005). Starting in 2008 all colonies were assessed, regardless of size, in contrast to previous years where only colonies greater than 10 cm in maximum linear dimension were assessed. Partial mortality of coral colonies was broken into two categories: recent and old. Recent partial mortality was characterized visually as skeleton not eroded (fine corallite structure still intact) and bare or with a thin veneer of sheeting or filamentous algae. Recent partial mortality is typically visible for up to three months following tissue loss. Old partial mortality was characterized as skeleton eroded and covered with turf or macroalgae. Old partial mortality is a transition from recent mortality and typically lasts up to 1–6 years (Smith et al. 2008). Diseases were conservatively categorized into recognized Caribbean scleractinian diseases and syndromes that included bleaching, black band disease, dark spots disease, white plague, stony coral tissue loss disease, and yellow band (blotch) disease (following Bruckner 2007). Acroporid corals were extremely rare at the study sites; thus, their associated diseases (white band and white pox) are not presented. Bleaching was assessed as abnormal paling of the colony, and, when present, the severity of the bleaching (paling or total whitening) and the area of the colony affected were assessed. For each transect, the prevalence of coral impairment categories was calculated as the number of colonies with partial mortality, disease, or bleaching divided by the number of colonies assessed. Also, for affected colonies in each transect the average three-dimensional surface area (%), or extent of the colony affected was also estimated for each impairment category. METHODS 25 FISH CENSUS Fish abundance, size, and diversity were recorded using transects and roving diver surveys. There have been changes in protocol through the years to make initial methods more comparable to other regional sampling programs, to increase detection of rare, commercially important species, and to streamline logistics. Fish species’ identity, abundance, and size were assessed along at each site conducted over 15 minutes per transect. Prior to 2009, belt transect were 30 x 2 m in size. Starting in sampling year 2009 belt transects were enlarged to 25 m x 4 m, increasing the survey area however from 2009 through 2011, two surveys were done per replicate, the first counting all non- site attached fish and the return survey along the transect line surveying smaller, site attached fish. In 2012, transects were again modified, and single surveys (25 m x 4 m) were conducted per transect replicate, counting both site attached and non-site attached fish on a single survey. This change brought TCRMP assessment methodologies in line with NOAA Biogeography Branch methods at that time (Menza et al. 2006; Friedlander et al. 2013). Before 2019 ten transects were conducted at each site. A retrospective analysis showed that nine transects were sufficient to capture within-site variability, and so the number of transects was reduced to nine starting in 2019. All transects were begun at a random location on the site and were laid in a random direction. Fish were sized by fork length recorded into size-bin categories (cm): 1-5, 6-10, 11-20, 21-30, 31-40, etc. up to >150. This sampling strategy is not optimized for noting the presence and abundance of small (<5 cm) gobies and blennies, and the taxa were inconsistently recorded. Roving diver survey (RDS) were also conducted at each site to estimate site fish diversity. Prior to 2016, RDS surveys in water depths less than 25 m were 30 minutes in duration and, because of restrictions in dive length, were 15 minutes in deeper water. Retrospective analysis showed that almost all diversity was captured in the first 15 METHODS 26 minutes of the survey. Therefore, to make deeper sites comparable, the methods were switched to 15 minute RDS at all sites in 2016. In all surveys, all species encountered were recorded except blennies and gobies. Divers also counted the number of Diadema antillarum sea urchins within 1 m on either side of a transect. From 2001 – 2008 this occurred along the 6 – 10 m long benthic transects. Starting in 2009, urchins were assessed along 25 x 2 m belt transects corresponding to the return of the fish transects. The mean number of sea urchins per 100 m2 was calculated for each site. Data from all fish surveys were transcribed to Microsoft Excel and Access spreadsheets and analyzed for descriptive statistics of reef fish assemblage structure. Starting in 2021, data entry occurred in a customized data entry system with built-in quality control parameters. Data presented in individual site summaries represents data collected for the current report period only. Due to diving constraints, completion of all fish surveys at five sites in St. Croix could not be achieved during the annual sampling mission for the current survey year (2023). As a result, these surveys were ‘picked up’ during the spring 2024 mission. More details with specific dates and locations can be found in Table 2. TCRMP MONITORING SUMMARY 27 Territorial Coral Reef Monitoring Summary TEMPERATURE The general sea surface temperature for the USVI is presented here as background for overall coral condition and site-specific temperatures presented in the “Site Summaries” section (Fig. 9). Figure 9. Sea surface temperatures and coral degree heating weeks of the US Virgin Islands from 1984 – 2024. The black line is a linear fit of the sea surface temperature showing a 0.024˚C increase in temperature per year (y = 0.0237/year * x - 26.75). Degree heating weeks (DHW) are calculated as the 12-week rolling sum of temperatures exceeding 1°C over the monthly maximum mean temperature, which is estimated at 28.5°C for the USVI (NOAA 2006). DHW values above 4 are associated with the onset of bleaching, and above 8 with the onset of mass bleaching and coral mortality. (Optimum Interpolation Sea Surface Data, OISST, from https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html, accessed April 17, 2025 by Lauren Olinger Ph.D.) BENTHIC COMMUNITIES AND CORAL REEF HEALTH Benthic cover was monitored at 34 monitoring sites and coral health was monitored at 33 sites in 2023. Raw data for benthic coverage, coral health, algae heights, and benthic temperature can be found at https://www.vitcrmp.org/data-and-methods . In addition, TCRMP MONITORING SUMMARY 28 updated benthic cover for each site individually is presented in the “Site Summaries” section. CORAL COVER The cover of hard corals decreased at most sites immediately following the 2005 coral bleaching event but losses in coral cover following the 2010, 2012, 2019, and 2023 bleaching events were less evident (Fig. 10). Recovery following bleaching in 2005 was marginal, especially in mesophotic sites. Direct impacts of the more recent bleaching events (2019 and 2023) are likely obscured by overall chronic decline of coverage regardless of the temperature conditions. Sites that had low coral cover to start generally lost far less relative cover from bleaching stress. While part of this may be attributed to the difficulty of detectability as coral cover values nearer to 0, it is also true that these sites tend to be dominated by small species that are more resistant to bleaching and disease related mortality (Smith et al. 2013b). However, prior to impacts of SCTLD in 2019, slow and irregular upward trajectories were notable at some sites, including Black Point, Botany Bay, Cane Bay, Fish Bay, Lang Hind, Salt River West, Salt River Deep, Seahorse, and St. James (Fig. 11; Fig. 12). Generalities that might indicate why these sites are recovering are difficult to pinpoint, but the coral communities in these reefs are all diverse. This diversity may contribute to recovery as thermally sensitive, but fast-growing species, such as Agaricites spp. and Porites porites, may push increases in coral cover. The deepest site, Ginsburgs Fringe, has lost site lost 87% of its coral cover in the past decade, in what appears to be a steady continuous decline (Fig. 11). Multiple co-occuring stressors are apparent at this TCRMP site, including invasive lionfish and high cover of the macroalgae Lobophora variegate. However, the most obvious cause of disturbance is anchoring on the reef (Smith et al. 2019b). A derelict reef claw anchor with at least 30m of polypropylene line was seen embedded in the monitoring site in 2014. Since damage has been recurrent it is likely that one or a few people are repeatedly anchoring on the edge to fish the Grammanik Bank. These activities have broken large plates and overturned portions of a large section of the large Agaricia spp. colonies that compose this reef. TCRMP MONITORING SUMMARY 29 Ginsburgs Fringe is just along the border of the Grammanik Bank Federal Fisheries Managed Area and the site of a multi-species spawning aggregation, including Nassau grouper and yellowfin grouper (Kadison et al. 2006; Nemeth et al. 2006)). Anchoring was likely for the purpose of fishing within the seasonal closed area, as there is little other obvious reason for anchoring at the shelf edge in deep water. Impacts to the corals and other essential fish habitat at this site may indirectly harm fishing in the US Virgin Islands. Additionally, there are a few shallow sites that have experienced chronic degradation. Magens Bay is highly impacted by sedimentation since it is largely enclosed, surrounded by steep hillsides under constant development (sediment run-off), and is susceptible to strong winter swells (Rothenberger et al. 2008). On the other hand, Savana is an offshore and uninhabited island next to the typically clear waters of the Virgin Passage. Degradation at this site can be largely attributed to encrusting alga (Ramicrusta textilis), which has been competing for benthic space and slowly decreasing coral cover by overtopping colony margins. In January 2019 stony coral tissue loss disease (SCTLD) was first observed at the Flat Cay monitoring site. Over the span of a few years, it spread across all reefs in the U.S. Virgin Islands, causing significant tissue loss and mortality, especially to highly and moderately susceptible species (most brain corals and bouldering corals; Brandt et al. 2021). During its spread, numerous organizations in the USVI coordinated response teams to attempt to mitigate and slow the spread of the disease. However, dramatic declines in species diversity and coral coverage still occurred. The TCRMP locations most adversely affected by SCTLD include Kings Corner, Flat Cay, and Brewer’s Bay with relative coral cover losses of 67%, 64%, and 59%, respectively, in the three years following disease introduction. TCRMP MONITORING SUMMARY 30 Figure 10. Mean hard coral, macroalgal (encrusting and erect), and epilithic algal community (EAC) coverage (±SEM) across all TCRMP sites during sampling from 2002-2024. Data is split into mesophotic (≥27 m), offshore (7-24 meters; ≥2 km offshore), and nearshore (6-17 meters; <2 km offshore). TCRMP MONITORING SUMMARY 31 Figure 11. Coral cover (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2001 – spring 2024. TCRMP MONITORING SUMMARY 32 Figure 12. Coral cover (±SE) across St. Croix TCRMP monitoring sites from 2001 – spring 2024. TCRMP MONITORING SUMMARY 33 ALGAL COVER Epilithic Algal Community Cover Algae show the highest inter-annual variability of any group of benthic organisms and is largely due to seasonality. The cover of epilithic algae is no exception since it tends to negatively covary with more ephemeral macroalgae (Fig. 10). Epilithic algae is important as it can indicate substrates grazed by herbivores and therefore open to the settlement of sessile epibenthic animals, including coral. Therefore, declines in the cover of epilithic algae (or increases in the cover of macroalgae and filamentous cyanobacteria) could be an early indication of declining herbivory at sites. Some offshore sites, such as Eagle Ray, Buck Island-St. Croix, and Savana, appear to have a declining abundance of epilithic algae over the extent of the monitoring. Large recent declines in epilithic algae at Savana are due to increases in Ramicrusta. Epilithic algae coverage appears to be highest at mesophotic sites, surpassing all other macroalgal coverage in most years (Fig. 13). Macroalgal Cover Macroalgal cover has been increasing at most TCRMP sites, particularly where coral cover has declined (Fig. 10). At sites where there was no loss of coral cover, increased macroalgae may be due to declining grazing, such as at Eagle Ray, the Buck Islands (St. Thomas and St. Croix), Cane Bay, Meri Shoal, South Capella, and Sprat Hole. Additionally, this might occur when resident herbivores communities are already at the threshold of maximum grazing rates (Williams et al. 2001). This process could be enhanced where herbivores numbers are falling due to fishing. At Savana the large increase in macroalgae in was due to the expansion in encrusting Ramicrusta textilis, (Ramicrusta is classified with macroalgae in TCRMP data summaries despite its largely encrusting morphology). This increase in Ramicrusta was also at the expense of epilithic algae. TCRMP MONITORING SUMMARY 34 Filamentous Cyanobacteria Filamentous cyanobacteria cover has been increasing at many sites in the TCRMP since the 2005 coral bleaching event. In many cases this was a multi-year peak that has abated, but at some sites high cover relative to baseline has persisted until 2014 (Fig. 13). This is particularly true at many sites on St. Croix. The increased incidence of filamentous cyanobacteria can be an indication of disturbance, increased nutrient inputs, and insufficient grazing (Fong and Paul 2011). In addition, filamentous cyanobacteria often have secondary metabolites that deter grazing on the cyanobacteria and on palatable macroalgae coated with cyanobacteria (Fong et al. 2006). Filamentous cyanobacteria can inhibit the recruitment of coral larvae (Kuffner et al. 2006) and has been observed interacting at the borders of adult coral (TCRMP, unpub. data). Monitoring the trends of filamentous cyanobacteria in USVI reef systems will be increasingly important in future years to understand the factors influencing bloom formation and which reefs are most vulnerable. TCRMP MONITORING SUMMARY 35 Figure 13. Mean algal coverage (±SEM) across TCRMP monitoring sites from 2005-spring of 2024. All macroalgae (grey line/orange shading) includes all erect and encrusting algae combined, as well as cyanobacteria. Other macroalgae (purple) includes all erect macroalgae except Dictyota (orange) and Lobophora (blue) TCRMP MONITORING SUMMARY 36 OTHER BENTHIC COVER Gorgonian and Antipatharian Cover The cover of gorgonians and antipatharians has been consistent or increasing at most monitoring sites throughout the years of monitoring (Fig. 14). Black Corals (antipatharians) are rare and when they occur tend to be more prominent in deep monitoring sites. For many gorgonian species their abundance tends to peak in shallow water where there is constant swell (benthic orbital turbulence). Both gorgonians and antipatharians did not seem sensitive to the thermal stress events in 2005, 2010, and 2012 (Tsounis and Edmunds 2017), however bleaching was observed on many gorgonians in 2023 (author, pers. obs). In most cases, gorgonians are a relatively minor component of cover because of their upright growth form and small branches which makes them less detectable in planar imagery. At Coral Bay and Fish Bay on the south side of St. John the cover of gorgonians has been increasing through the monitoring time series, which has also been observed by a separate research group in the same area (Tsounis and Edmunds 2017). Magens Bay had previously shown increasing gorgonian cover, but this has reversed somewhat in later monitoring years. These sites are known to have water quality issues and a high influx of terrestrial sediments. It is possible that inputs of nutrients from terrestrial run-off and poor sewage disposal are stimulating pelagic primary productivity (Furnas et al. 2005) and increasing the abundance of gorgonians that can feed heterotrophically on water column resources (De'ath and Fabricius 2010). Sponge Cover There is an indication of slightly increasing sponge cover at select nearshore and offshore sites—but general sponge coverage appears steady (Fig. 14). Increases were most pronounced at sites around St. Thomas, including Black Point, Buck Island, Flat Cay, and Magens Bay. Sites such as Black Point, South Water, and Flat Cay showed declines in sponge cover in the 2017 monitoring year, possibly due to the impacts of Hurricane Irma and Hurricane Maria (Gochfeld et al. 2020). TCRMP MONITORING SUMMARY 37 Figure 14. Mean benthic cover (±SEM) of gorgonians, sponges, and zooanthids from 2005- spring of 2024 at TCRMP locations. TCRMP MONITORING SUMMARY 38 FISH COMMUNITIES Raw data from fish census can be found at: https://www.vitcrmp.org/data-and- methods. The following metrics are separated by northern USVI (St. Thomas & St. John) and St. Croix due to the differing assemblages of fish present at these locations. These dissimilarities are primarily driven differences in topography across the islands: St. Croix’s shelf is much shorter and has a steeper edge, resulting in less fish habitat compared to the abundant Orbicellid banks in the northern UVSI (Smith et al. 2019). This limited habitat, combined more intense fishing pressure, has likely led to greater depletion of commercially important species (Kadison et al. 2017). Abundance and Biomass Northern USVI: The fish transect surveys conducted in 2023 on the 18 sites in the northern USVI’s documented 144 species and 40 families. A total of 37,108 individuals were recorded with a mean density of 229 ± 32 fish 100m-2 across all sites. The biomass of fish surveyed across all sites totaled 3,590 kg with a mean of 22 ± 5 kg 100m-2 at each site. Fish diversity was highest in offshore sites, with 115 species noted across 11 sites. In 2023, fish density was very similar across nearshore and offshore sites, with an average of 233 ± 27 100m-2 fish seen at each site. Mesophotic sites had a slightly lower average density, with only 215 ± 43 individuals 100m-2 observed. Conversely, biomass was much higher in mesophotic sites (64 ± 36 kg 100m-2), whereas biomass in nearshore and offshore environments averaged only 11 ± 1 kg 100m-2. This large discrepancy was primarily driven by occurrence of schools of larger pelagic fishes on shelf edge sites and by large serranids and lutjanids observed at one site (Grammanik Tiger FSA) as sampling occurred during peak cubera snapper (Lutjanus cyanopterus) spawning (August; Biggs and Nemeth, 2016). Average biomass observed in each transect at Grammanik was 170 ± 32.5 kg 100m-2, thirteen times higher than the average biomass across all other sites (13 ± 0.1 kg 100m-2). St. Croix: The fish transect surveys conducted in 2023 on the 15 sites in St. Croix documented 142 species and 43 families. A total of 25,926 individuals were recorded with a mean abundance across all sites of 192 ± 25 fish 100m-2. The calculated biomass of fish surveyed across all sites totaled 1,182 kg with a mean of 9 ± 3 kg 100m-2 at each site. This is TCRMP MONITORING SUMMARY 39 much lower than the estimated biomass in northern USVI (22 ± 5 kg 100m-2), likely due to higher fishing pressure removing more of the large-bodied species (Kadison et al. 2017). In St. Croix, fish diversity was lowest in mesophotic sites, and higher in nearshore and offshore sites, which both observed 107 unique species. Fish abundance per site ranged from ~330 fish per transect (Cane Bay) to ~100 fish per transect (Salt River Deep). Overall, density was highest in nearshore sites (244 ± 32 fish 100m-2 ) followed by offshore sites (200 ± 26 fish 100m-2). As with northern USVI, mesophotic sites had the lowest abundance, with an average of 131 ± 13 individuals observed per transect. Contrasting high biomass in northern USVI mesophotic sites, deeper sites in St. Croix had the lowest biomass estimates, with only 5.7 ± 1.2 kg 100m-2, indicating smaller fish on average. Nearshore and offshore environments had almost double the biomass of mesophotic sites, with an average of 10.3 ± 2.2 kg 100m-2. Species Composition Northern USVI: The most common species observed were striped parrotfish (Scarus iseri; 15.7% of total fish observed), bluehead wrasse (Thalassoma bifasciatum; 12.9%), blue chromis (Chromis cyanea; 10.8%), bicolor damselfish (Stegastes partitus; 7.2%), and creole wrasse (Clepticus parrae; 6.0%). These five species comprised 19% of the fish biomass observed in the northern USVI. Other species contributed significantly to overall biomass in St. Thomas and St. John include stoplight parrotfish (Sparisoma viride; 5.7% of total biomass), redband parrotfish (Sparisoma aurofrenatum; 5.0%), and cubera snapper (Lutjanus cyanopterus; 4.9%) – most of which were all observed at Grammanik. St. Croix: The five most abundant species observed in St. Croix were the same five as in the northern USVI in 2023, however their relative distributions varied from the northern USVI’s. Blue chromis (Chromis cyanea; 17.7% of total fish observed) was most common, followed by bluehead wrasse (Thalassoma bifasciatum; 17.1%), bicolor damselfish (Stegastes partitus; 10.1%), creole wrasse (Clepticus parrae; 5.8%), and striped parrotfish (Scarus iseri; 5.5%). These five species comprised 16.3% of the fish biomass observed in St. Croix. Other significant contributions to St. Croix’s biomass came from the black durgeon (Melichthys niger; 5.8% of total biomass), redband parrotfish (Sparisoma aurofrenatum; TCRMP MONITORING SUMMARY 40 5.0%), blue tang (Acanthurus coeruleus; 5.0%), and ocean surgeonfish (Acanthurus bahianus; 4.2%). Table 3. The 2023 species richness for belt transects and roving diver surveys (RDS). Belt Transects (25x4) RDS Total Number of Species Mean species per transect (±SE) Total Number of Species Nearshore Cane Bay 68 26.3±1.4 51 Great Pond 38 16.8±1.2 46 Jacks Bay 58 20.3±1.2 54 Castle 52 23.8±1.2 48 Salt River West 57 21.8±2.0 48 Sprat Hole 55 24.2±0.7 62 Coculus Rock 54 23.6±1.1 57 Black Point 55 22.7±1.2 60 Brewers Bay 46 20.1±1.3 43 Botany Bay 56 22.6±1.1 56 Coral Bay 41 19.0±0.9 42 Fish Bay 65 22.4±2.7 60 Magens Bay 53 23.6±1.5 52 Offshore Eagle Ray 53 21.3±1.5 43 Buck Island, St. Croix 59 23.2±1.3 51 Kings Corner 61 26..2±1.4 57 Mutton Snapper FSA 55 22.4±1.2 56 Buck Island, St. Thomas 68 28.1±0.9 61 Seahorse Cottage Shoal 72 26.4±1.1 52 South Capella 66 24.0±1.5 52 South Water 53 22.6±1.3 58 Flat Cay 53 22.6±1.2 59 Savana Island 64 27.9±1.9 58 St. James 56 23.2±2 46 Mesophotic Buck Island STX Deep 49 18.7±1.4 44 Cane Bay Deep 49 14.9±0.9 39 Lang Bank EEMP 62 22.4±1.1 55 Lang Bank Red Hind FSA 53 18.9±1.7 49 Salt River Deep 53 17.1±1.2 48 College Shoal East 52 21.9±0.9 43 Ginsburg’s Fringe - - - Grammanik Tiger FSA 61 23.4±1.2 52 Hind Bank East FSA 62 25.4±1.0 59 Meri Shoal 47 18.8±0.9 43 TCRMP MONITORING SUMMARY 41 Fish Abundance Total yearly fish abundances across nearshore, offshore, and mesophotic sites are shown in Figures 16 and 17. As in previous years, total fish abundance showed high variability across sites and strata. In deeper reefs, these changes can be attributed to the presence or absence of the prolific small pelagic fishes, (most often the creole wrasse, Clepticus parrae) that vary annually and seasonally. Total fish abundance in the northern USVI was similar to the previous year (~36,000 individuals) however St. Croix total abundance was lower in 2023 than 2022 (25,656 vs. 29,280 fish respectively). Sites with the highest overall fish abundance in 2023 were Botany Bay, Sprat Hole, and Cane Bay. High fish abundance at these sites was influenced by large schools of small bluehead wrasse (T. bifasciatum), blue and brown chromis (Chromis cyanea and Chromis multilineata), and striped parrotfish (S. iseri) observed during the surveys. The sites with the lowest fish abundance were Salt River Deep and Cane Bay Deep. These mesophotic wall sites, defined by agariciid corals and high silt loads, continue to also have low species richness values and low biomass each year during sampling (Fig. 15). Figure 15. A representative photo of the mesophotic wall sites on St. Croix, characterized by sloping walls, high silt loads, Agarica spp. coverage, and low fish abundance, biomass, and richness (photo credit: L. Henderson). TCRMP MONITORING SUMMARY 42 Figure 16. Fish abundance (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2003-2023. TCRMP MONITORING SUMMARY 43 Figure 17. Fish abundance (±SE) across St. Croix TCRMP monitoring sites from 2003-2023. TCRMP MONITORING SUMMARY 44 Fish Biomass Total fish biomass for all sites and years is shown in Figures 19 and 20. As with abundance, biomass was highly variable across strata, sites, and years. No temporal pattern is obvious, and differences appear to be seasonal or natural variation. Overall average biomass was higher in 2023 than in 2022, however this was almost entirely driven by the very high (>150 kg 100m-2) biomass observed at Grammanik Tiger FSA. Sampling this year occurred during cubera snapper (Lutjanus cyanopterus) spawning (August; Biggs and Nemeth, 2016) and biomass this species accounted for 89% of the total biomass estimated at Grammanik. Other sites with high biomass included the two other sites on the St. Thomas’ shelf edge (College Shoal East and Hind Bank East FSA), as well as King’s Corner, which regularly boasts high fish biomass, abundance, and diversity each year. All three mesophotic sites on the northern VI shelf edge vary seasonally due to the annual or seasonal presence/absence of large pelagic fishes which serve as the primary influence on biomass values. The same influx of spawning large pelagic fishes has not been noted on any of the mesophotic St. Croix sites, although they are usually sampled a couple months later, outside of spawning season for these species. In fact, the sites with two lowest biomass values in 2023 were Cane Bay Deep and Buck Island STX Deep. Jack’s Bay and Eagle Ray also had notably lower biomass values; all four of these sites are in St. Croix. Figure 18. Nassau grouper (Epinephelus striatus) observed while sampling at Grammanik Tiger FSA (photo credit: N.Krampitz). TCRMP MONITORING SUMMARY 45 Figure 19. Mean fish biomass (±SE) across St. Thomas and St. John TCRMP monitoring sites from 2003-2023. TCRMP MONITORING SUMMARY 46 Figure 20. Mean fish biomass (±SE) across St. Croix TCRMP monitoring sites from 2003-2023. TCRMP MONITORING SUMMARY 47 BLACK SPINED SEA URCHIN DIADEMA ANTILLARUM In general, the shallowest sites, e.g., Great Pond and Coculus Rock, support the greatest abundance of Diadema antillarum, hereafter referred to as Diadema (Fig. 21). At Coral Bay there was a high abundance of Echinometra spp. that has not been quantified, but the abundance seems to have declined after 2017. This species seems to be the dominant grazer and effectively removes most macroalgal cover, but also contributes apparently high bioerosion (gnawed coral bases). Future monitoring might consider targeted monitoring of these species at certain sites. The overall abundance of Diadema at TCRMP sites has remained somewhat variable over the years but has generally increased since 2010 (Fig. 22). Exceptions to this are major declines seen in 2017, following due to two Category 5 hurricanes, and 2022, following a mass mortality event (Hewson et al. 2023). Despite significant declines in Diadema density in early 2022, many juvenile Diadema began to reappear on many reefs by the end of the year, suggesting population numbers are growing instead of declining further. Where they occurred, overall density of Diadema increased from 0.23 ± 0.15 urchins/100m-2 in 2022 to 1.00 ± 0.68 urchins/100m-2 in 2023. However, Diadema were only observed at 7 TCRMP locations in 2023 (vs. 15 in 2021); and of those urchins that were observed, most were small or juveniles, whose functionality as a key herbivore in controlling algal growth would be limited. TCRMP MONITORING SUMMARY 48 Figure 21. Average density (±SE) of the black spined sea urchin (Diadema antillarum) at 33 TCRMP monitoring sites in 2023. Note the log scale Figure 22. Average density (±SE) of Diadema antillarum at TCRMP sites from 2012-2023.