We assessed the condition of the St. Thomas East End Reserves, establishing a baseline from which we can evaluate the effectiveness of restoration activities. This is the first reserve-wide integrated ecological assessment that includes chemical contaminants in sediments, coral, fish, and conch; toxicity of sediments; nutrient levels; and sedimentation rates, and a biological survey of the entire STEER.
Why We Care
The extensive mangroves, seagrass beds and coral reefs of the St. Thomas East End Reserves (STEER) support tourism and fishing and protect the shorelines of St. Thomas, U.S. Virgin Islands. The watershed also hosts several potential sources of pollution including a large active landfill, marinas, commercial/industrial activities, a Superfund Site, and residential areas served by individual septic systems.
Elevated levels of chemical contaminants have been found in the watershed, and anecdotal information from the U.S. Virgin Islands Department of Planning and Natural Resources (DPNR) suggests that fish from Mangrove Lagoon within the STEER are affected by the pollution. The DPNR has stated that filling the information gap on the effects of chemical contaminants in the STEER is critical to making informed management decisions, to protect and enhance this valuable resource.
What We Did
We are established a baseline assessment of chemical contaminants and toxicity, along with living marine resources in the STEER. In 2011, we quantified chemical contaminants in sediments and documented the impact of those contaminants on marine life via a series of sediment-toxicity bioassays. In 2012, we conducted the first-ever biological survey of the entire STEER. We also collected coral, conch, and fish for chemical contaminant analysis, and began monthly monitoring for nutrients and sedimentation. Based on the results from the 2011 work, DPNR asked NCCOS to further evaluate northern Benner Bay for chemical contaminants, specifically tributyltin or TBT, along with heavy metals in both surface sediments and sediment cores. The sediment core work was used to assess the changes in chemical contamination over time.
What We Found
Higher levels of chemical contaminants were found in Mangrove Lagoon and Benner Bay in the western portion of the study area, than in the eastern area. The concentrations of polychlorinated biphenyls (PCBs), DDT (dichlorodiphenyltrichloroethane), chlordane, zinc, copper, lead and mercury were above a NOAA sediment quality guideline at one or more sites, indicating impacts may be present in more sensitive species or life stages in the benthic environment. Copper at one site in Benner Bay, however, was above a NOAA guideline (ERM) indicating that effects on benthic organisms were likely. The boat hull antifoulant ingredient tributyltin or TBT, was found at the third highest concentration in the history of NOAA’s National Status and Trends (NS&T) Program. Based on these results, DPNR asked us to further evaluate the level of contamination in northern Benner Bay, in both surface sediments and in sediment cores. Results from this work indicated some of the sediment cores were highly contaminated. Copper, for example, was found as high as 1,540 μg/g in a sediment core, which is more than five times higher than the NOAA sediment quality guideline (SQG) concentration associated with toxic effects on benthic organisms. In addition, TBT was found at greater than 5,000 ng Sn/g, nearly an order of magnitude higher than the highest concentration (550 ng Sn/g) ever recorded in NOAA’s NS&T Program, and over an order of magnitude higher than an upper screening value established to help determine when additional testing or assessments would be advisable at EPA Superfund sites. Results from the biological survey in the STEER indicated that fish metrics were similar to other U.S. Caribbean monitoring locations, using the same methodology. Areas in northern Mangrove Lagoon and northern Benner Bay could not be surveyed by divers due to low visibility and concern for diver health related to water quality. Biomass for grunts and snapper were higher in St. Croix than in the STEER, and may reflect the role that the extensive mangroves in the Mangrove Lagoon/Benner Bay area play, as nursery areas for juvenile fishes.