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Deepwater Horizon oil spill affects dolphins, ecosystem

By Dawn Brazell | News Center | Nov. 24, 2014

Hollings Marine Lab - Deepwater Horizon oil spill
Photo provided by NOAA


Dr. Jean Hermann takes a dental x-ray of a dolphin onboard the RV Megamouth during dolphin health assessments in Barataria Bay, Louisiana. 

Beyond the cuteness factor, bottlenose dolphins draw the interest of researcher Lori Schwacke for their role as a top level predator.

Schwacke, Ph.D., chief of Oceans & Human Health Branch of the National Oceanic and Atmospheric Administration (NOAA), began researching the health of bottlenose dolphins in the Gulf of Mexico following the Deepwater Horizon (DWH) oil spill. Schwacke said the dolphin health assessments in the aftermath of the DWH were only possible because of the long-term research her team had been conducting to understand the health of marine mammals in coastal waters, and the factors that influence their health.

Dr. Lori Schwacke, Ph.D 
Dr. Lori Schwacke 
Though her group at the Hollings Marine Lab (HML) also does research with other marine animals, dolphins hold a particular allure for her.

“These dolphins are top level predators in coastal ecosystems in the Gulf, and the loss of a top level predator can have cascading effects within that ecosystem. Also, the health of the dolphins reflects the condition of the broader ecosystem. Our dolphin health research is critical so that we are not only prepared to assess the impacts of events, such as the DWH spill, but also so that we can understand effects of more gradual, but long-term environmental changes.”

HML researchers continued efforts in 2013 to assess injuries to dolphins in the Gulf of Mexico as a result of the DWH oil spill, expanding health assessment studies to include dolphins in Mississippi and Alabama waters in addition to the previously sampled dolphin population in Barataria Bay, Louisiana.

A dolphin health assessment study in 2011 led by HML researchers found that dolphins in Barataria Bay, an area that received significant and prolonged oiling from the DWH spill, suffered from a number of disease conditions. Barataria Bay dolphins showed symptoms of hypoadrenocorticism, consistent with adrenal toxicity previously described in experimental studies of mink exposed to oil. “Cortisol, produced by the adrenal gland, is essential for responding to stressful conditions. Barataria Bay dolphins had abnormally low cortisol concentrations and this could ultimately lead to a number of complications and in some situations even death.”

The Barataria Bay dolphins also were five times more likely to have moderate to severe lung disease, sometimes characterized by lung masses.

 Deep Water Horizon
Photo Provided
 This map shows locations of dolphins captured and sampled for health assessments and then released during 2013 in the Barataria Bay, Mississippi Sound and Sarasota Bay areas.
The findings surprised them because of the severity of the disease in the animals.

The health assessment study was repeated in June 2013 to examine whether the health of Barataria Bay dolphins had improved. Researchers from the HML Genomics Core joined the collaboration and sampling was conducted to examine how gene expression profiles may differ among dolphins with different disease conditions. New field-based techniques for dental examination, including radiographs, also were added.

Sampling also was expanded to include Mississippi and Alabama coastal waters, and improved satellite-linked tags were used to monitor dolphin movements for several months following their evaluation.

Laboratory analyses of samples and follow-up photographic monitoring in the study sites will continue in 2014, she said. The potential population-level impacts of the DWH spill are still being assessed, but the high prevalence and severity of disease conditions and an ongoing rise in dolphin deaths in the northern Gulf of Mexico raise significant concern and suggest the need for continued monitoring, she said.

Deep Water Horizon - Dolphin
Provided by NOAA
A dolphin has been hoisted onboard a specially designed processing boat and is being given a comprehensive health examination by an interdisciplinary research team consisting of experts in veterinary medicine, toxicology, marine mammal biology, and wildlife epidemiology. Dr. Cynthia Smith conducts an ultrasound while the team monitors the dolphin and prepares for the next procedures. 
“This is the first peer-reviewed publication to come out on what we’re finding in the Gulf with regard to mammals following the DWH oil spill. We are seeing significant health issues in the dolphins,” she said. “The issues are consistent with the effects you might expect to see after exposure to oil. Particularly with marine mammals, which are long-lived species, if there are health effects, it may take years to fully quantify the ultimate impacts on survival and reproduction.”

That ties into work being done in other labs, such as that of MUSC researcher Louis Guillette, Ph.D. Schwacke, who is a part of MUSC’s Marine Biomedicine and Environmental Sciences program, said the HML collaborative environment is a scientific catalyst. “Having someone down the hall who you can bounce ideas off of is fantastic.”

 For more information on MUSC’s Marine Biomedicine and Environmental Sciences, visit its website.



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