The State of Coral Reef Ecosystems of the United States
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STATUSSTATUS OFOF CORALCORAL REEFSREEFS ININ THETHE U.S.U.S. VIRGINVIRGIN ISLANDSISLANDS DonDon Catanzaro,Catanzaro, CarolineCaroline Rogers,Rogers, ZandyZandy Hillis-Starr,Hillis-Starr, RickRick Nemeth,Nemeth, andand MarciaMarcia TaylorTaylor THE STATUS OF THE CORAL diversity occur on geological features REEFS OF THE U.S. VIRGIN offshore at greater depths. ISLANDSISLANDSISLANDS By D. Catanzaro, C. Rogers, Z. Together the USVI total Hillis-Starr, R. Nemeth, M. roughly 347 km2 of land Taylor area. St. Croix is the largest of the three USVI islands at Introduction 207 km2 (34 km by 10 km) with a relatively high The U.S. Virgin Islands (USVI) is a western mountainous tip. U.S. territory located approximately This island has coral growth 1,000 nmi southeast of Miami and along much of the insular 45 nmi east of Puerto Rico. Coral shelf with a well-developed reefs are found around the three barrier reef on the eastern main islands of St. Croix, St. John, end, and deep coral walls on and St. Thomas, as well as most the north shore. St. Croix is offshore cays. Fringing reefs, deep the only island with a reefs (wall and shelf-edge), patch permanent source of reefs, and spur and groove Figure 186. Shallow-water reef freshwater. St. Thomas is communities cover 61% of the 2 formations are present on all three region (Photo: William Harrigan). the second largest at 83 km islands although only St. Croix has well (22 km by 5 km) and St. developed barrier reefs. Bank reefs and John is the smallest of the three USVI 2 scattered patch reefs with high coral islands at 52 km (14 by 5 km). Recently NOAA mapped USVI coral reefs Figure 187. Benthic habitats of Buck Island Channel, St. Croix, USVI were mapped from and associated aerial photographs ( Credit: John Christensen). ecosystems to LegendLegendLegend approximately a Sand Mud depth of 20 m Seagrass/Continuous Seagrass/70-90% and delineated a Seagrass/50-70% total submerged Seagrass/30-50% 2 Seagrass/10-30% area of 485 km Macroalgae/Continuous Macroalgae/Patchy/50-90% (Kendall 2001b, Macroalgae/Patchy/10-50% Monaco et al. Reef/Linear Reef Reef/Spur and Groove Reef 2001). Deeper Reef/Patch Reef (Individual) water reef Reef/Patch Reef (Aggregated) Reef/Scattered Coral-Rock habitats off the Reef/Colonized Pavement Reef/Colonized Bedrock USVI islands Reef/Col. Pav. with Chan. have yet to be Hardbottom/Reef Rubble Hardbottom/Uncol. Pav. mapped. Coral Hardbottom/Uncol. Bedrock reef and Hardbottom/Uncol. Pav. with Chan. Land colonized hard- U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS Mangrove U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS Artificial bottom habitats Unknown comprised 297.9 No Attributes 131131131131131131 km2 and accounted for 61% of the mapped additional site on St. John has eight non- area; submerged aquatic vegetation randomly located transects which have covered 160 km2 or 33% of the mapped been sampled for three years. total, and unconsolidated sediments and uncolonized hard-bottom habitat Live scleractinian coral cover varies at comprised 23 km2 or the remaining 4%. these sites from a low of 5.8% (Buck Island, St. Croix) to a high of 22.8% Condition of Coral Reefs (Mennebeck, St. John). It should be noted that the site with non-randomly The long-term datasets for the USVI located transects has a live scleractinian represent some of the best temporal data coral cover of 45.3% (Tektite, St. John). available for the Caribbean (Connell Results of the repeated sampling are varied 1997). Although monitoring and research but overall, 76% of transects showed has occurred on all three USVI islands, declines in the amount of live coral cover consistent long-term datasets exist only for when the first year is compared to the third St. John and Buck Island, St. Croix (e.g. year. Percent of transects exhibiting 1988 to present) and have been collected declines at individual sites are as follows: primarily by the Department of the 40% (Yawzi, St. John), 65% (Buck Island, Interior, National Park Service St. Croix), 75% (Mennebeck, (NPS) and U.S. Geological Survey St. John), 95% (Newfound, (USGS). Most of these studies are St. John), and 62% (Tektite, targeted in individual bays that St. John). might not be representative of conditions within the entire USVI NOAA monitoring funds (Table 1). were received by the USVI Territorial Government in 2001 and University of Corals and Other Invertebrates Virgin Islands conducted the – NPS has conducted and supported study. The first year of this long-term monitoring on St. John project supported six sites on (site of Virgin Islands National St. Croix (six transects each) Park, VINP) and Buck Island, St where coral, sea urchin Croix (site of Buck Island Reef (Diadema antillarum), and National Monument, BINM) since reef fish have been 1988. Over time, statistical rigor Figure 188. Monitoring in the monitored. Live scleractinian has significantly increased due to USVI using videography (Photo: coral cover varied from a improvements in technology and USGS). low of 6% (Lang Bank) to sample design. For the last three years 25% (Sprat Hole) (Nemeth et al. in press). USGS and NPS scientists have Monitoring will be repeated in 2002. collaborated on long-term monitoring of coral reefs using a comprehensive protocol – Branching based on use of a digital video camera White-band Disease along randomly chosen transects (Miller acroporid species are most susceptible to and Rogers 2001, Rogers et al. in press). White-band Disease. At BINM, elkhorn Acropora palmata This protocol is one of the most coral ( ) cover fell from statistically rigorous methods to monitor 85% in 1976 to 5% in 1988 because of coral reefs in the world. A total of 79 mortality from the combination of storms et al randomly located transects at four sites and disease (Rogers . 1982, Gladfelter (three in St. John and one at Buck Island, 1991). White-band Disease is still occasionally seen throughout the USVI U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS St. Croix) have been repeatedly sampled for two or more years. An additional site at and shallow reef areas are now graveyards Buck Island, St. Croix (20 transects) has of dead elkhorn coral, with branches and been sampled for one year and one fragments interspersed among algal 132132132132132132 none on St. Thomas or St. Croix (Nemeth et al. in press). At Buck Island, Black- band Disease is seen on Diploria colonies but typically on fewer than 10 colonies a year (Zandy Hillis-Starr pers. comm). A limited, recent assessment across the USVI found 3.4% (St. Thomas), 7.6% (St. John), and 2.0% (St. Croix) of coral colonies over 25 cm in diameter showing signs of disease (Nemeth et al. in press). Figure 189. White-band disease on elkhorn coral (Photo: Other Diseases – Small USVI patch reefs Caroline Rogers). of Porites porites have died from an covered skeletons still upright in normal unknown disease (Rogers 1999, J. Miller growth position. pers. comm., B. Kojis pers. comm.) and some of these reefs have been dead for There is current evidence that elkhorn over 12 years (see Beets et al. 1986). coral is recovering in the USVI. Porites porites is not known to be Recruitment of elkhorn coral colonies may susceptible to either White-band or Black- be increasing and biologists from NPS, band Disease. USGS, and UVI are now monitoring and mapping this species at several USVI sites. Sea fan disease, caused by the fungus Aspergillis syndowii, occurs in sea fans on Plague – In July 1997, conspicuous white St. John reefs (G. Smith pers. comm.). patches of necrotic tissue began to appear This pathogenic strain has been isolated on scleractinian corals in several bays from air samples taken during African dust around St. John. Tissue samples have events, suggesting a possible link between confirmed that Plague is affecting these air quality and sea fan condition. corals. It has now been observed on 14 coral species. The disease can progress up Sea Urchins – According to Lessios et al. to 0.5 cm/day but does not always result in (1984), the condition of USVI coral reefs total colony mortality, however diseased has been significantly impacted by a die- portions never recover. Monthly surveys off of the long-spined sea urchin (Diadema on one St. John reef have documented new incidence of disease every month from Figure 190, A. Long-spined sea urchin feeding on reef algae 1997 to present (Miller et al. in press) (Photo: NOAA Photo Gallery). B. Urchin dead from a Caribbean-wide disease. (Photo: Caroline Rogers). making this the most destructive disease active on St. John. Black-band Disease – This disease primarily infects major reef-building corals such as Montastraea annularis and Diploria strigosa (Edmunds 1991, Richardson et al. 1997). In 1988, Edmunds (1991) found very low incidence of Black- B band Disease (0.2%) on corals in seven sites in the U.S. and British Virgin Islands. U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS Nemeth reported 1.2% on St. John and A U.S. VIRGIN ISLANDS U.S. VIRGIN ISLANDS 133133133133133133 around St. John and St. Thomas in 1981, 1985, 1990, 1996, and 2000 (Wood and Olsen 1983, Boulon 1987, Friedlander et al.