Emily Chan
For years, mercury contamination in marine environments has been a significant public health concern. Now, dolphins have emerged at the forefront of this issue.
In a new study, researchers have found elevated levels of mercury in dolphins across the southeastern United States, particularly along the Florida and Georgia coasts.
As apex predators at the top of the ocean’s food chain, dolphins accumulate mercury and other pollutants in their tissues through the consumption of a variety of smaller fish that make up their diet, including croaker, spot, squid, and shrimp. All of these species are vulnerable to the toxic element and are consumed by people as well.
The accumulation of mercury in dolphins not only threatens their survival but also serves as a warning sign of health hazards to humans from the ocean and the broader ecological impacts of mercury pollution.
“As a sentinel species, the bottlenose dolphin data presented here can direct future studies to evaluate mercury exposure to human residents,” wrote the authors of the study.
The team of researchers examined 175 samples of skin that were collected from bottlenose dolphins in estuaries between 2005 and 2019. The dolphins lived in the St. Joseph, Choctawhatchee, and Biscayne Bays in Florida, Sapelo Island, and Skidaway and Turtle/Brunswick River estuaries in Georgia.
The measured mercury in dolphin skin correlates directly with the methylmercury in their other organs and tissues. Mercury is converted to methylmercury by bacteria in the water. The methylmercury is then eaten or absorbed by small fish and passed up the food chain to larger species like dolphins.
In St. Joseph Bay, dolphins averaged 14,193 nanograms of mercury per gram in the skin. They had the highest recorded mercury levels out of all the dolphins that were tested.
According to Mackenzie Griffin, the lead author of the study and a biologist at the National Oceanic and Atmospheric Administration (NOAA), the high mercury levels in the bay may be partially due to industrial activities.
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