Assessing bottlenose dolphin health as an indicator of overall ecosystem health; an ongoing study in the Turtle/Brunswick River Estuary and Sapelo Island National Estuarine Research Reserve
For my dissertation, I am working with NOAA to compare bottlenose dolphin populations near EPA superfund sites in Georgia to those at a nearby national estuarine reserve. The Turtle/Brunswick River Estuary (TBRE) located in Glynn County, Georgia, includes the Turtle and Brunswick Rivers, St. Simons Sound, St. Simons Island, and Jekyll Island. The LCP Chemical manufacturing plant, to the west of the city of Brunswick, is currently on the National Priority List (NPL), a list of all toxic waste sites that are eligible for federal assistance toward clean-up.
The LCP Chemical NPL site covers approximately 550 acres of tidal marsh adjacent to the Turtle River and 15km upriver from St. Simons Sound. Over the past 70 years, LCP Chemical has operated an oil refinery, paint manufacturing plant, and chlor-alkali plant on this site. These industrial influences have resulted in high levels of mercury, polychlorinated biphenyls (PCBs), and semi-volatile contaminants within the soils, groundwater, and marsh biota surrounding the region. In addition to the LCP Chemical plant, three other NPL sites are in and around Brunswick; Terry Creek Dredge Spoil/Hercules Outfall, Hercules 009 Landfill, and Brunswick Wood Preserving. Hercules Inc., the company responsible for the Terry Creek Dredge Spoil/Hercules Outfall and Hercules 009 Landfill, manufactured an organochlorine pesticide known as toxaphene, from 1948-1980. The Terry Creek Dredge Spoil/Hercules Outfall is in close proximity to Dupree and Terry Creeks which empty into St. Simons Sound. High concentrations of toxaphene in all trophic levels surrounding this site have been identified.
In contrast to the TBRE, the Sapelo Island National Estuarine Research Reserve (SINERR), located approximately 30km northeast of Brunswick, encompasses the fourth largest and one of the most pristine barrier island systems along the Georgia coast. The SINERR is a part of the National Estuarine Research Reserve System (NERRS) and is a focus of long-term ecological research projects such as water quality monitoring, primary productivity assessment, and fisheries sampling. Thus, the TBRE and SINERR offer the opportunity to investigate polluted and relatively pristine field sites that are geographically adjacent to each other. NOAA and its partners have recently conducted a study, which included portions of the TBRE and SINERR, to assess indicators of ecosystem health including nutrient loads, pathogen indicators, water quality, sediment contaminants, and oyster tissue contaminants. As a complementary project, contaminant exposures of bottlenose dolphins are also being measured.
Bottlenose dolphins are long-lived, apex predators that bio-accumulate persistent organochlorine contaminants (POCs) in their lipid-rich blubber. Along the southeastern United States, many dolphin populations demonstrate high levels of site-fidelity to localized regions. Thus, the bottlenose dolphin has been identified as a sentinel of coastal ecosystem health. Bottlenose dolphins also forage on a variety of recreational and commercial marine species, suggesting they may also be an indicator for human health risks in a particular region.
Remote biopsy dart samples from bottlenose dolphins in both regions have been obtained and a subset of these samples has been analyzed to identify persistent organochlorine contaminants (POC), including 66 PCB congeners, 7 PBDE congeners and a number of organochlorine pesticides. Chemical analyses are being conducted at the Hollings Marine Laboratory by the National Institute of Standards and Technology (NIST) laboratory. Preliminary data suggest extremely high levels of PCBs in dolphins sampled from the TBRE. Surprisingly, relatively high levels of PCBs were also found in dolphins sampled from SINERR. However, without knowing the ranging patterns of the biopsy-sampled individual dolphins, the origin of these contaminants is currently unknown. For this reason, photo-identification research to investigate the distribution and movement patterns of dolphins along this area of the Georgia coast is essential.
This project will be the first to evaluate and compare seasonal abundance, site-fidelity, habitat utilization patterns, and contaminant specificity for bottlenose dolphins across two geographically adjacent, yet ecologically different regions of the Georgia coastline. Intensive seasonal mark-recapture surveys utilizing photo-identification of individuals’ dorsal fins will be used to determine bottlenose dolphin abundance in both regions. Comparing sighting histories for all identified individuals will provide site-fidelity indices (i.e. amount of time dolphins are spending within each of the two areas) throughout the course of the study. Strahler Stream Order, a quantitative technique used to classify estuarine habitats, will be used in combination with sighting distribution to characterize habitat utilization of bottlenose dolphins within and between the TBRE and SINERR field sites. In addition to remote biopsy dart samples from known dolphins, sighting histories will be used to identify fine-scale geographic contaminant specificity of bottlenose dolphins in both regions; are there contaminant congeners specific to the TBRE and SINERR regions? In addition, these results may also identify a pathway for contaminants in a salt marsh estuarine ecosystem; are dolphins absorbing these contaminants by traveling between the TBRE and SINERR regions, or are the contaminants reaching the dolphins in another way, such as dolphin prey traveling between regions?
Assessing ecosystem health requires a multi-faceted analysis of all trophic levels of an ecosystem. Prior studies have identified high levels of PCBs and other contaminants surrounding NPL sites in Brunswick. The biopsy dart samples from bottlenose dolphins in both the TBRE and SINERR have provided preliminary evidence for elevated levels of PCBs in bottlenose dolphins within both regions. However, there are still numerous questions left unanswered to identify the overall health of these two ecosystems. Identifying bottlenose dolphin abundance, site-fidelity, habitat use, and contaminant specificity for these regions is one method toward providing insight into bottlenose dolphin health and thus ecosystem health within the TBRE and SINERR.
This research would not be possible without funding from NOAA Fisheries Service, Georgia Department of Natural Resources, and Chicago Zoological Society.