Geology topics

Research about U.S. Virgin Islands

Source-linked reports with geographic coverage including U.S. Virgin Islands.

At least 19 recordsLinked to original sources

USGS2025

Where to restore and conserve? A regional benefit cost analysis of coral reef protection and restoration for coastal flood resilience

Momentum is growing for the management of coral reefs as a strategy to reduce climate risks in tropical coastlines. Yet, quantification of the life-time costs, impacts, and benefits remains limited. This study provides one of the first rigorous, spatially explicit, regional-scale Benefit:Cost Analyses (BCA) for coral reef restoration and was designed to meet the BCA requirements of major hazard mitigation funding and programs. This study simulates coastal flooding using a hydrodynamic model under different scenarios representing current coral reef conditions, reef degradation, and reef restoration. These coastal flood maps are used to estimate socioeconomic damages, which are included in a BCA to assess cost-effectiveness and priority areas for coral reef conservation and restoration. The United States Virgin Islands is used as a case study given recent impacts from storms and their new policy that declares reefs as natural infrastructure. The results show that flood risk across the islands of Saint Croix, Saint John, and Saint Thomas is $51.4 million USD per year. Annually, coral reefs prevent flood damages to 481 people and $43.6 million USD of infrastructure, which represents 87 % of the flood risk. These results identify the communities that could receive the greatest benefits from coral conservation and restoration, which overlap significantly. Coral reef restoration is found to be a cost-effective strategy for flood mitigation although how reefs are restored matters. Hybrid coral reef restoration provides greater flood mitigation benefits than ecological restoration, but its cost-effectiveness is overall lower given its greater costs. Many coastal areas have benefit:cost ratios exceeding 1.5, which complies with typical government agencies’ requirements for accessing hazard mitigation funds. This valuation framework helps provide rigorous regional-scale quantification of nature-based coastal protection solutions for coastal risk management decisions.

Journal of Environmental Management↗

USGS2025

Population vulnerability of residents, employees, and cruise-ship passengers to tsunami hazards of islands in complex seismic regions: A case study of the U.S. Virgin Islands

Reducing the potential for loss of life from tsunamis is challenging on islands located in complex seismic regions given the multiple sources that surround islands, differences among islands in the amount of time needed to evacuate before wave arrival, and the high number of residents, employees, and tourists in tsunami-hazard zones. We examine variations in population vulnerability in island communities to multiple tsunami threats and use the United States territory of the U.S. Virgin Islands (USVI), including St. Thomas Island, St. John Island, and St. Croix Island, as our case study. We estimate the tsunami-hazard exposure of residents, employees, and cruise-ship passengers on vessels docking at USVI maritime facilities, as well as model pedestrian travel times out of inundation zones for 13 credible tsunami scenarios. Results indicate that the threat to life safety in USVI posed by tsunamis is not equal among the three islands, both in terms of the magnitude of people in hazard zones and the amount of time available to evacuate for the various scenarios. The number of employees and cruise-ship passengers in tsunami-hazard zones is orders of magnitude higher than the number of residents, suggesting that risk assessments that only account for residents are under-estimating threats to life safety from tsunamis. Finally, reducing departure delays has a greater impact than increasing pedestrian travel speeds on reducing the number of people that may have insufficient time to evacuate hazard zones before wave arrival.

U.S. Virgin Islands↗

USGS2024

Pathology of lesions in corals from the US Virgin Islands after emergence of stony coral tissue loss disease

Stony coral tissue loss disease (SCTLD) was first documented in Florida in 2014 and has since spread through the Caribbean causing unprecedented mortality in more than 20 species of corals. The cause of SCTLD is unknown, but bacteria are suspected based on regression of gross lesions in some corals treated with antibiotics. Limited pathology studies on SCTLD exist, but it is likely that ‘SCTLD’ is a general term encompassing tissue loss disease of unexplained origin. Here, we examined pathology of lesions in corals from the US Virgin Islands where SCTLD has recently emerged. The typical histologic lesion of SCTLD in Florida corals was lytic necrosis comprising vacuolation and necrosis of mucus cells with erosion of mesoglea and misshapen endosymbionts with variably sized intracytoplasmic granules and common occurrence of filamentous viral-like particles in endosymbionts visible on electron microscopy (EM). In contrast, USVI corals had mainly lytic mucus cell hypertrophy and necrosis with no involvement of mesoglea, endosymbiont pathology at the light microscopy level was less evident, and VLP were rarely seen on EM. We suspect SCTLD is likely more complex with multiple presentations and potential etiologies depending on geographic region. Further pathological studies from other regions might help refine the case definition of SCTLD.

St. John↗

USGS2024

Quantifying the coastal hazard risk reduction benefits of coral reef restoration in the U.S. Virgin Islands

Coastal habitat restoration, especially of coral reef ecosystems, can significantly reduce the exposure of coastal communities to natural hazards and, consequently, the risk of wave-driven flooding. Likewise, reef degradation can increase coastal flood risks to people and property. In this study, the valuation of coral reefs in the United States Virgin Islands (USVI), along the coasts of St. Croix, St. John, and St. Thomas, demonstrated the social and economic benefits provided by these natural defenses. Across the territory, more than 481 people and $31.2 million of infrastructure were estimated to receive protection from coral reefs per year (2010 U.S. dollars). In 2017, Hurricanes Irma and Maria significantly damaged coral reefs throughout the archipelago. By combining engineering, ecological, geospatial, social, and economic data and tools, this study provided a rigorous valuation of where potential coral reef restoration projects could help rebuild these damaged habitats and decrease the risks from coastal hazards faced by USVI’s reef-fronted communities. Multiple restoration scenarios were considered in the analysis, two of which are detailed in this report. These include (1) ‘Ecological’ restoration, where restoration creates a structure that is 0.25 m high and 25-m-wide reef, and (2) ‘Hybrid’ restoration, where restoration creates a structure that is 1.25 m high and 5 m wide. There are many ways that such structures could be developed. In the hydrodynamic analyses, there are no assumptions about how the restoration is developed. Many practitioners of both coral (and oyster reef) restoration consider that a reef height of 0.25 m might be delivered from planting corals alone and that 1.25 m might require a combination of artificial structures and coral planting. In a third scenario, the analysis investigated the reduction of protection benefits that would occur through the reduction of 1 meter of naturally occurring reef height due to reef degradation. The reduction of protection due to the loss of reefs can also be interpreted as the protection value of the existing reefs. In all studied restoration scenarios, it was assumed that the planting of corals would enhance hydrodynamic roughness, effectively dissipating incident wave energy and reducing the potential for coastal flooding. A standardized approach was employed to strategically locate potential restoration projects along the entire linear extent of existing reefs bordering the USVI, and to identify where coral reef restoration could offer valuable benefits in flood reduction. Potential restoration projects were only located within the existing distribution of reefs across the region, even though numerous sites were positioned far offshore (2-3 km), and some were at relatively deep depths (up to 7 m). Risk-based valuation approaches were followed to delineate flood zones at a 10 m 2 resolution along the entire region's reef-lined shorelines for all the potential coral reef restoration scenarios. These were subsequently compared to flood zones without coral reef restoration. The potential reduction in coastal flood risk provided by coral reef restoration, and the protection value of existing reefs, were quantified utilizing the latest information available at the time of analysis from the U.S. Census Bureau, Federal Emergency Management Agency (FEMA), and Bureau of Economic Analysis for return-interval storm events. The change in Expected Annual Damages (EAD), a metric indicating the annual protection gained due to coral reef restoration, was calculated based on the damages associated with each storm probability. The findings suggest that the benefits of reef restoration are spatially variable within the USVI. In some areas, the analysis showed limited benefits from reef restoration, which may be attributed to the depth or offshore distances of proposed restoration sites. However, there were a number of key areas where reef restoration could have substantial benefits for flood risk reduction. The annual flood risk reduction attributed to potential ‘ecological’ coral reef restoration in the USVI was 99 people and $6.1 million (2010 U.S. dollars). The Benefit-to-Cost Ratio (BCR) for this restoration approach was found to be larger than 1 (i.e., cost-effective) along 11% of the St. Croix coastline, 4.9% of the St. John coastline, and 8.7% of the St. Thomas coastline. This analysis offers stakeholders and decision-makers a spatially explicit and rigorous evaluation that illustrates how, where, and when potential coral reef restoration efforts in St. Croix, St. John, and St. Thomas could be instrumental to reducing coastal storm-induced flooding. Understanding areas where reef management, recovery, and restoration could effectively reduce climate hazard-related risks is crucial to protect and enhance the resilience of coastal communities in USVI.

Report↗

USGS2023

Per- and polyfluoroalkyl substances (PFAS) in United States tapwater: Comparison of underserved private-well and public-supply exposures and associated health implications

Drinking-water quality is a rising concern in the United States (US), emphasizing the need to broadly assess exposures and potential health effects at the point-of-use. Drinking-water exposures to per- and poly-fluoroalkyl substances (PFAS) are a national concern, however, there is limited information on PFAS in residential tapwater at the point-of-use, especially from private-wells. We conducted a national reconnaissance to compare human PFAS exposures in unregulated private-well and regulated public-supply tapwater. Tapwater from 716 locations (269 private-wells; 447 public supply) across the US was collected during 2016–2021 including three locations where temporal sampling was conducted. Concentrations of PFAS were assessed by three laboratories and compared with land-use and potential-source metrics to explore drivers of contamination. The number of individual PFAS observed ranged from 1 to 9 (median: 2) with corresponding cumulative concentrations (sum of detected PFAS) ranging from 0.348 to 346 ng/L. Seventeen PFAS were observed at least once with PFBS, PFHxS and PFOA observed most frequently in approximately 15% of the samples. Across the US, PFAS profiles and estimated median cumulative concentrations were similar among private wells and public-supply tapwater. We estimate that at least one PFAS could be detected in about 45% of US drinking-water samples. These detection probabilities varied spatially with limited temporal variation in concentrations/numbers of PFAS detected. Benchmark screening approaches indicated potential human exposure risk was dominated by PFOA and PFOS, when detected. Potential source and land-use information was related to cumulative PFAS concentrations, and the number of PFAS detected; however, corresponding relations with specific PFAS were limited likely due to low detection frequencies and higher detection limits. Information generated supports the need for further assessments of cumulative health risks of PFAS as a class and in combination with other co-occurring contaminants, particularly in unmonitored private-wells where information is limited or not available.

U.S. Virgin Islands↗

USGS2023

Hawksbill and green turtle niche overlap in a marine protected area, US Virgin Islands

Studying how species interact with their environment and other co-occurring species are 2 main aspects of ecology. For marine turtles, ocean currents drive migratory routes and may determine the location of surrounding foraging grounds. As a result, circumglobal species like the hawksbill turtle Eretmochelys imbricata and green turtle Chelonia mydas adapt to diverse foraging habitats and employ varied feeding strategies. Dietary specializations may reduce competition for available food and space resources between co-occurring hawksbill and green turtles in US Virgin Island shallow reef habitats. This study analyzed isotopic data from immature hawksbill (n = 49; range: 18.7-49.8 cm straight carapace length [SCL]) and green turtles (n = 225; range: 24.1-69.4 cm SCL) to examine foraging niche. We used nitrogen stable isotope (δ 15 N) values as an indicator of trophic positioning and carbon stable isotope (δ 13 C) values as a habitat variable. Turtles were hand-captured across an 8 yr period (2012-2019), which facilitated the distinction of isotopic patterns in both the environment and among individual turtles. Understanding variations in habitat, community dynamics, and dietary consumption allowed us to utilize a 5 point framework to translate isotopic space to foraging niche. We found that the site’s relatively stable environmental conditions allow for isotopic overlap between hawksbill and green turtles despite the specialized feeding strategies each species employs. We also underscore the need to evaluate species-specific tissue turnover estimates as evidenced by the influence of tropical storms on recaptured turtle isotopic signatures. These findings inform our understanding of resource use for these imperiled species at our study site and are useful for future global isotopic comparisons.

U.S. Virgin Islands↗

USGS2020

Structural impacts, carbon losses, and regeneration in mangrove wetlands after two hurricanes on St. John, U.S. Virgin Islands

Hurricanes Irma and Maria ravaged the mangroves of St. John, U.S. Virgin Islands, in 2017. Basal area losses were large (63–100%) and storm losses of carbon associated with aboveground biomass amounted to 11.9–43.5 Mg C/ha. Carbon biomass of dead standing trees increased 8.1–18.3 Mg C/ha among sites, and carbon in coarse woody debris on the forest floor increased 1.9–18.2 Mg C/ha, with effects varying by mangrove typology. While St. John has only ~45 ha of mangroves, they exist as isolated basins, salt ponds, and fringe mangroves; the latter sometimes support diverse marine communities. Salt pond and fringe mangroves had proportionately more organic carbon (46.3 Mg C/ha) than inorganic carbon (1.1 Mg C/ha) in soils than isolated basins. Soil organic carbon was also appreciable in isolated basins (30.8 Mg C/ha) but was matched by inorganic C (36.7 Mg C/ha), possibly due to adjacent land use history (e.g., road construction), previous storm overwash, or geomorphology. Soil nitrogen stocks were low across all typologies. Mangroves had limited regeneration 26 months after the storms, and recovery on St. John may be hindered by pre-storm hydrologic change in some stands, and potential genetic bottlenecks and lack of propagule sources for expedient recovery in all stands.

St Johns↗

USGS2017

Resident areas and migrations of female green turtles nesting at Buck Island Reef National Monument, St. Croix, U.S. Virgin Islands

Satellite tracking in marine turtle studies can reveal much about their spatial use of breeding areas, migration zones, and foraging sites. We assessed spatial habitat-use patterns of 10 adult female green turtles (Chelonia mydas) nesting at Buck Island Reef National Monument, U.S. Virgin Islands (BIRNM) from 2011 – 2014. Turtles ranged in size from 89.0 – 115.9 cm CCL (mean + SD = 106.8 + 7.7 cm). The inter-nesting period across all turtles ranged from 31 July to 4 November, and sizes of the 50% core-use areas during inter-nesting ranged from 4.2 – 19.0 km2. Inter-nesting core-use areas were located up to1.4 km from shore and had bathymetry values ranging from -17.0 to -13.0 m. Seven of the ten turtles remained locally resident after the nesting season. Five turtles (50%) foraged around Buck Island, two foraged around the island of St. Croix, and the other three (30%) made longer-distance migrations to Antigua, St. Kitts & Nevis, and Venezuela. Further, five turtles had foraging centroids within protected areas. Delineating spatial areas and identifying temporal periods of nearshore habitat-use can be useful for natural resource managers with responsibility for overseeing vulnerable habitats and protected marine turtle populations.

U.S. Virgin Islands↗

USGS2015

Transplantation of storm-generated coral fragments to enhance Caribbean coral reefs: A successful method but not a solution

In response to dramatic losses of reef-building corals and ongoing lack of recovery, a small-scale coral transplant project was initiated in the Caribbean (U.S. Virgin Islands) in 1999 and was followed for 12 years. The primary objectives were to (1) identify a source of coral colonies for transplantation that would not result in damage to reefs, (2) test the feasibility of transplanting storm-generated coral fragments, and (3) develop a simple, inexpensive method for transplanting fragments that could be conducted by the local community. The ultimate goal was to enhance abundance of threatened reef-building species on local reefs. Storm-produced coral fragments of two threatened reef-building species [ Acropora palmata and A. cervicornis (Acroporidae)] and another fast-growing species [ Porites porites (Poritidae)] were collected from environments hostile to coral fragment survival and transplanted to degraded reefs. Inert nylon cable ties were used to attach transplanted coral fragments to dead coral substrate. Survival of 75 reference colonies and 60 transplants was assessed over 12 years. Only 9% of colonies were alive after 12 years: no A. cervicornis ; 3% of A. palmata transplants and 18% of reference colonies; and 13% of P. porites transplants and 7% of reference colonies. Mortality rates for all species were high and were similar for transplant and reference colonies. Physical dislodgement resulted in the loss of 56% of colonies, whereas 35% died in place. Only A. palmata showed a difference between transplant and reference colony survival and that was in the first year only. Location was a factor in survival only for A. palmata reference colonies and after year 10. Even though the tested methods and concepts were proven effective in the field over the 12-year study, they do not present a solution. No coral conservation strategy will be effective until underlying intrinsic and/or extrinsic factors driving high mortality rates are understood and mitigated or eliminated. Rev. Biol. Trop. 60 (Suppl. 1): 59-70. Epub 2012 March 01.

Revista de Biología Tropical: International Journa↗

USGS2014

Marine and inland fishes of St. Croix, U. S. Virgin Islands: an annotated checklist

An historical account is given for the ichthyological research at St. Croix, U. S. Virgin Islands, followed by an annotated list of 544 species of mostly marine shore fishes known or reported from the island to depths of 200 m. Color photographs are included for 103 of these species. Collections made at Buck Island Reef National Monument with the ichthyocide rotenone in 2001 and 2005 increased the known ichthyofauna by about 80 species. The rational for inclusion of each species in the checklist is given, with remarks for those species for which additional documentation or voucher specimens are needed. Reports of species known or presumed to have been based on misidentifications are discussed. Of the total marine fish fauna of the island, 404 species (75%) are restricted to the western Atlantic Ocean, (223 of these species are essentially Caribbean endemics that do not occur south of the Amazon River outflow), and no St. Croix endemic species are known. An additional 17 species (3.2%) also occur at mid-Atlantic islands, 57 species (10.6 %) are limited to both sides of the Atlantic Ocean, and 40 species (7.4%) have circumtropical distributions. The four most species-rich families are the Gobiidae (47 species), Serranidae (groupers and sea basses, 41), Labridae (wrasses and parrotfishes, 31), and Labrisomidae (scaly blennies, 27). Literature reports of Mosquitofish, Gambusia sp., from St. Croix apparently were based on misidentifications of a different introduced poeciliid genus. Four species of the amphidromus goby genus Sicydium occur in St. Croix inland waters, together with three established introduced species (one cichlid and two poeciliids). Also included are one catfish (Ictaluridae) and three sunfishes (Centrarchidae) known only from ponds. The Lionfish, Pterois volitans , the only introduced marine species, was first reported from St. Croix in 2008 and is now common despite control efforts.

Caribbean;St. Croix↗

USGS2013

Early signs of recovery of Acropora palmata in St. John, US Virgin Islands

Since the 1980s, diseases have caused significant declines in the population of the threatened Caribbean coral Acropora palmata . Yet it is largely unknown whether the population densities have recovered from these declines and whether there have been any recent shifts in size-frequency distributions toward large colonies. It is also unknown whether colony size influences the risk of disease infection, the most common stressor affecting this species. To address these unknowns, we examined A. palmata colonies at ten sites around St. John, US Virgin Islands, in 2004 and 2010. The prevalence of white-pox disease was highly variable among sites, ranging from 0 to 53 %, and this disease preferentially targeted large colonies. We found that colony density did not significantly change over the 6-year period, although six out of ten sites showed higher densities through time. The size-frequency distributions of coral colonies at all sites were positively skewed in both 2004 and 2010, however, most sites showed a temporal shift toward more large-sized colonies. This increase in large-sized colonies occurred despite the presence of white-pox disease, a severe bleaching event, and several storms. This study provides evidence of slow recovery of the A. palmata population around St. John despite the persistence of several stressors.

St. John↗

USGS2011

Data from in situ Observations of Fish Traps Set by Fishermen in St. John Waters, U.S. Virgin Islands, 1992-94

In order to estimate (1) the trapping pressure within Virgin Islands National Park (VINP) waters, (2) the effect of fish traps on park marine resources (both fishes and habitats), and (3) the effectiveness of park regulations in protecting marine resources, traps set by fishers were visually observed and contents censused in situ in 1992, 1993, and 1994, around St. John (U.S. Virgin Islands), within and outside of park waters. A total of 1,340 individual fish (56 species and 23 families) were identified and their lengths estimated for the 211 of 285 visually censused traps that contained fish. This dataset includes for each censused trap: location, depth, substrate/habitat, trap type and construction details, in or out of park waters, and species and estimated fork length (in centimeters) of each individual fish in a trap. Analysis and interpretation of this dataset are provided in previously published reports by the author.

St. John↗

USGS2009

High diversity and abundance of scleractinian corals growing on and near mangrove prop roots, St. John, US Virgin Islands

A narrow zone of red mangroves fringes the shorelines of four small bays in Hurricane Hole, within Virgin Islands Coral Reef National Monument (VICRNM) on St. John. In two of these bays, Otter Creek and Water Creek, a particularly high abundance and diversity of corals are growing directly on or near the prop roots (Fig. 1 a,b,c). To date, 28 coral species have been found: Stephanocoenia intersepta , Agaricia sp., Agaricia agaricites , Siderastrea siderea , S. radians , Porites porites , P. astreoides , P. furcata , P. divaricata , Favia fragum , Diploria strigosa , D. labyrinthiformis , D. clivosa , Manicina areolata , Colpophyllia natans , C. amaranthus , Montastraea annularis , M. faveolata , M. franksi , M. cavernosa , Oculina diffusa , Meandrina meandrites , Dendrogyra cylindrus , Scolymia cubensis , Mycetophyllia sp., Eusmilia fastigiata , Cladocora arbuscula , and Tubastrea coccinea . The size of many of the colonies, including some M. faveolata and C. natans colonies over 1 m across (Fig. 1 b), indicate that they survived the 2005/2006 bleaching and disease event that caused losses of over 60% of the coral cover on St. John reefs (Rogers et al. 2008 ). Shading by the mangroves possibly reduced the thermal and photic stress on these corals. The coral diversity in these mangroves may be higher than for other Caribbean mangrove systems. Few published papers include data on corals in these habitats. Two comprehensive reviews of the biology of mangroves make no reference to corals on or near prop roots (Kathiresan and Bingham 2001 ; Nagelkerken et al. 2008 ). The number of corals in Hurricane Hole, particularly the new recruits on the prop roots (Fig. 1 c), may have increased since the establishment of the VICRNM in 2001, as boaters are not permitted to overnight in these bays or to tie their boats to the mangrove trees as was done in the past.

St. John↗

USGS2009

Extensive coral mortality in the US Virgin Islands in 2005/2006: A review of the evidence for synergy among thermal stress, coral bleaching and disease

In the summer/fall of 2005, extensive coral bleaching on reefs in the US Virgin Islands (USVI) was associated with sea water temperatures exceeding 30°C. Almost all coral species bleached, including Acropora palmata , which bleached for the first time on record in the USVI. As water temperatures cooled, corals began to regain their normal coloration. However, a severe disease outbreak then occurred on deeper, non-acroporid reefs. The disease demonstrated signs consistent with white plague. Monitoring of coral cover along previously established long-term transects on several reefs in St. John and St. Croix was intensified. Data on bleaching and disease were collected before, during and after this bleaching/disease episode. Average coral cover declined by over 50%, from 21.4% to 10.3% at the long-term study sites, within one year of the onset of bleaching, declining further to 8.3% after two years. This loss of coral cover was greater than from all other stressors affecting the USVI reefs in preceding years, and no significant recovery is evident. Disease prevalence increased on bleached A. palmata colonies that were being monitored as well as on the colonies of other species on the deeper reefs. Bleached A. palmata colonies had more disease (primarily white pox and other un-described diseases) than unbleached colonies. The non-acroporid corals that bleached most severely suffered the highest mortality from disease. Although the research summarized in this paper is not conclusive, the results suggest that high water temperatures lead to bleaching, which weakens corals and makes them more vulnerable to diseases.

U.S. Virgin Islands↗

USGS2008

EAARL submerged topography– U.S. Virgin Islands 2003

These remotely sensed, geographically referenced elevation measurements of Lidar-derived submerged topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), South Florida-Caribbean Network, Miami, FL; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate bathymetric datasets of a portion of the U.S. Virgin Islands, acquired on April 21, 23, and 30, May 2, and June 14 and 17, 2003. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

St John Island↗

USGS2006

Permanent 'phase shifts' or reversible declines in coral cover? Lack of recovery of two coral reefs in St. John, U.S. Virgin Islands

Caribbean coral reefs have changed dramatically in the last 3 to 4 decades, with significant loss of coral cover and increases in algae. Here we present trends in benthic cover from 1989 to 2003 at 2 reefs (Lameshur Reef and Newfound Reef) off St. John, US Virgin Islands (USVI). Coral cover has declined in the fore-reef zones at both sites, and no recovery is evident. At Lameshur Reef, Hurricane Hugo (1989) caused significant physical damage and loss of coral. We suggest that macroalgae rapidly colonized new substrate made available by this storm and have hindered or prevented growth of adult corals, as well as settlement and survival of new coral recruits. Overfishing of herbivorous fishes in the USVI and loss of shelter for these fishes because of major storms has presumably reduced the levels of herbivory that formerly controlled algal abundance. Coral cover declined at Newfound Reef from 1999 to 2000, most likely because of coral diseases. The trends that we have documented, loss of coral followed by no evidence of recovery, appear similar to findings from other studies in the Caribbean. We need to focus on functional shifts in the resilience of coral reefs that result in their inability to recover from natural and human-caused stressors.

U.S. Virgin Islands↗

USGS2002

Geology and hydrogeology of the Caribbean Islands aquifer system of the Commonwealth of Puerto Rico and the U.S. Virgin Islands

Poorly lithified to unconsolidated carbonate and clastic sedimentary rocks of Tertiary (Oligocene to Pliocene) and Quaternary (Pleistocene to Holocene) age compose the South Coast aquifer and the North Coast limestone aquifer system of Puerto Rico; poorly lithified to unlithified carbonate rocks of late Tertiary (early Miocene to Pliocene) age make up the Kingshill aquifer of St. Croix, U.S. Virgin Islands. The South Coast aquifer, North Coast limestone aquifer system, and Kingshill aquifer are the most areally extensive and function as the major sources of ground water in the U.S. Caribbean Islands Regional Aquifer-System Analysis (CI-RASA) study area. In Puerto Rico's South Coast ground-water province, more than 1,000 meters of clastic and carbonate rocks of Oligocene to Pliocene age infill the South Coast Tertiary Basin. The pattern of lithofacies within this basin appears to have been controlled by changes in base level that were, at times, dominated by tectonic movement (uplift and subsidence), but were also influenced by eustasy. Deposition of the 70-kilometer long and 3- to 8-kilometer wide fan-delta plain that covers much of the South Coast ground-water province occurred largely in response to glacially-induced changes in sea level and climate during the Quaternary period. Tectonic movement played a much less important role during the Quaternary. The North Coast ground-water province of Puerto Rico is underlain by homoclinal coastal plain wedge of carbonate and siliciclastic rocks that infill the North Coast Tertiary Basin and thicken to more than 1,700 meters. A thin basal siliciclastic sequence of late Oligocene age is overlain by a thick section of mostly carbonate rocks of Oligocene to middle Miocene age. Globigerinid limestone of late Miocene to Pliocene age crops out and lies in the shallow subsurface areas of northwestern Puerto Rico. Oligocene to middle Miocene age rocks tentatively can be divided into five depositional sequences and associated systems tracts; these rocks record carbonate and minor siliciclastic deposition that occurred in response to changes in relative sea level. The Cibao Formation represents the most complex of these sequences and contains a varied facies of carbonate, mixed carbonate-siliciclastic, and siliciclastic rocks that reflect differential uplift, subsidence, and transgression of the sea. Uplift, graben formation, and gradual shallowing of the sea are reflected within the bathyal-dominated sedimentary facies of the Kingshill Limestone in St. Croix, U.S. Virgin Islands. Reef-tract limestone beds of Pliocene age were subject to exposure, resubmergence, and meteoric leaching of aragonitic skeletal debris; these beds contain patchy lenses of dolomite that are restricted to a small, structurally-controlled embayment. The South Coast aquifer, the principal water-bearing unit of Puerto Rico's South Coast ground-water province, consists of boulder- to silt-size detritus formed by large and small coalescing fan deltas of Pleistocene to Holocene age. Deep well data indicates that it is possible to vertically separate and group a highly complex and irregular-bedded detrital sequence that underlies distal parts of the fan-delta plain into discrete water-bearing units if correlated with 30- to 40-meter thick, eustatically-controlled depositional cycles. Lithofacies maps show that greatest hydraulic conductivity within the fan-delta plain is generally associated with proximal fan and midfan areas. Distal and interfan areas are least permeable. Alluvial valley aquifers located in the western part of the South Coast ground-water province are important local sources of water supply and appear to contain some of the same physical and hydraulic characteristics as the South Coast aquifer. Older sedimentary rocks within the basin are poor aquifers; conglomeratic beds are well-cemented, and carbonate beds do not contain well-developed solution features, except locally where the beds are overlain by alluvium. Ground-water occurs under unconfined conditions in proximal and midfan areas. Confined conditions within deeper parts of the system and in interfan and some midfan areas are created largely by the intercalated nature of discontinuous fine-grained beds that retard vertical ground-water movement. The development of water resources in southern Puerto Rico has modified the hydrologic system of the South Coast aquifer considerably. Under predevelopment conditions, the South Coast aquifer was recharged in the unconfined, proximal fan and some midfan areas by infrequent rainfall and seepage from streams near the fan apex. Discharge occurred as seabed seepage, baseflow discharge along the lower coastal reach of streams, seepage to coastal wetlands, or evapotranspiration in areas underlain by a shallow water table. Under development conditions, seepage from irrigation canals and areal recharge from furrow irrigation represented a principal mechanism for recharge to the aquifer. Increased ground-water withdrawals in the 1960's and 1970's resulted in declines in the water table to below sea level in some places and intrusion of salt water into the aquifer. By the middle 1980's, a reduction in ground-water withdrawals and a shift from furrow irrigation to drip-irrigation techniques resulted in the recovery of water levels. Under present-day (1986) conditions, regional ground-water flow is coastward but with local movement to some well fields. In addition to the discharge mechanisms described above, ground-water discharges also to coastal canals. The North Coast limestone aquifer system consists of limestone, lesser amounts of dolomite, and minor clastic detritus of Oligocene to Pliocene age that form an unconfined upper aquifer and a confined lower aquifer; these aquifers are separated by a clay, mudstone, and marl confining unit. Topographic relief and incision of carbonate coastal plain rocks by streams are the principal factors controlling the direction of ground-water flow. The North Coast limestone aquifer system is recharged principally by precipitation that enters the upper and lower aquifers where they crop out. Regional groundwater movement from the upper aquifer is to the major rivers, wells, coastal wetlands, coastal, nearshore, and offshore springs, or as seabed seepage. Regional discharge from the lower aquifer is to the major rivers along its unconfined parts or where the confining unit has been breached by streams. Discharge from the lower aquifer also occurs in the San Juan area where the Mucarabones Sand provides an avenue for diffuse upward ground-water flow. Transmissivity within the upper limestone aquifer appears to be largely regulated by the thickness of the freshwater lens. The lens is thickest and transmissivity is greatest in interstream areas that lie in a zone that closely corresponds to the landwardmost extent of the underlying saltwater wedge. Hydraulic conductivity of the upper aquifer generally increases in a coastward direction and reflects lithologic control, karstification in the upper 30 to 100 meters of the section, and enhanced permeability in a zone of freshwater and saltwater mixing. Transmissivity of the lower aquifer is an order of magnitude smaller than that of the upper aquifer; highest transmissivities in the lower aquifer largely correspond to a coarse grainstone-packstone and coral-patch-reef depositional facies contained within the outcropping parts of the Montebello Limestone Member and its subsurface equivalents. Porosity within the North Coast limestone aquifer system is high in grainstone-packstones and low in wackestone and marl. Dolomitized zones and moldic grainstone-packstone strata are the most porous carbonate rocks, but occur in thin beds that usually are only a few meters thick. Processes of karstification that include the development of caverous zones and large vugs, and dissolution along possible regional fracture sets has enhanced permeability within the upper part of the aquifer system. Stratigraphic and lithologic control play an important role controlling permeability within the lower part of the system. The Kingshill aquifer of St. Croix, in large part, is composed of deepwater limestone that contains only microscopic pores and is poorly permeable; however, the upper part of the aquifer, a shallow-water skeletal and reef limestone, is fairly permeable, but restricted in areal extent. Permeability within these uppermost beds of the aquifer has been enhanced by meteoric leaching, dissolution within a mixing zone of saltwater and fresh water, and dolomitization. However, most large-yield wells completed in the Kingshill aquifer are also screened in alluvium that overlies or infills incised channels. The alluvial deposits serve as a temporary storage zone for rainfall, runoff, and ground water slowly entering the Kingshill aquifer.

Puerto Rico↗

USGS2000

Local variability but landscape stability in coral reef communities following repeated hurricane impacts

Coral reef community structure has remained remarkably stable over a 10 yr period within a small protected marine area despite repeated hurricane impacts. Local community dynamics have been highly variable, however. Sites that were destroyed by disease in the 1970s are showing little or no recovery, while sites less than a kilometre away that were devastated by Hurricane Hugo in 1989 are recovering well. Strong coral recruitment has occurred in shallow, exposed areas that showed the greatest hurricane impacts, and these areas are now more species rich than in 1988, although coral cover has not reached pre-hurricane levels. Coral colony survivorship has been high throughout most of the study area. Partial mortality rates were elevated for several years following Hurricane Hugo, but significant whole coral-head mortality only occurred during periods with hurricane impacts and only at the most exposed sites. Overall, the coral community has proved resilient to closely repeated major hurricane impacts. From a single case study we cannot attribute this resilience to the relatively low level of human impacts, but grazing fish populations have apparently remained high enough to keep macroalgae in check despite the mass mortality of the herbivore Diadema antillarum in the 1980s.

St. Croix↗