Turtles and Toxins

Military vessels and tourist attractions are well-known features along San Diego’s waterfront, but tucked away to the south is one of San Diego’s best kept aquatic secrets. Most people associate the East Pacific green sea turtle with exotic tropical destinations, but a resident population of the endangered reptiles inhabits the southern portions of San Diego Bay.

The turtles were first studied by Margie Stinson in the 1970s as part of her graduate research at San Diego State University (SDSU), and researchers at NOAA’s Southwest Fisheries Science Center (SWFSC) led by Peter Dutton and Jeffrey Seminoff subsequently have studied the group of about 60 sea turtles for the past 17 years. Now Scripps Institution of Oceanography at UC San Diego is providing collaborative expertise as part of a project that includes SDSU and the Port of San Diego.

For the past 10 years, Scripps Oceanography scientist Dimitri Deheyn has been developing biologically based methods for assessing the levels and ecological fate of contaminants in San Diego Bay. Working in a field known as “ecotoxicology,” Deheyn has used bioluminescent brittle stars, cousins of sea stars, as biological indicators of harmful chemical elements, which originate from a variety of sources. He is now part of a mentoring team for SDSU graduate student Lisa Komoroske aiming to more fully evaluate the health and ecology of San Diego’s green sea turtle population, which congregates in warm waters discharged by a power plant near Chula Vista, Calif., in south San Diego County.

“There are extensive beds of eel grass in the back bay, which are prime foraging grounds for the turtles,” said Komoroske. “Also, warm effluent water coming out of the South Bay power plant attracts them.”

SWFSC researchers have employed GPS and sonic tags, along with genetic testing, to determine that the South Bay turtles are part of a group that nests on beaches on the Revillagigedo Islands off the Pacific Mexican coast and migrates over a thousand miles north. Until recently San Diego was believed to be their northernmost residence, but last year NOAA scientists documented several off Long Beach, Calif., about 100 miles north of San Diego.

As part of the first scientific analysis of metals and contaminants in the San Diego population, Komoroske obtains blood samples and shell scrapings, or scutes, from the turtles, along with samples of the sea grasses and other items they consume. She and Deheyn then compare the metal signatures found within the turtles with the metal pollutants known to be present in the bay.

“The main question we are asking is if the sea turtle population is reflecting the contamination conditions found in San Diego Bay,” said Deheyn. “Lisa’s project is looking at all of the different components around the sea turtles.”

Komoroske dries, weighs, and dissolves habitat samples in acid and the resulting solution reveals the levels of metals present. The samples are then run through instruments called spectrophotometers that accurately test and quantify for 15 metal elements known to be potentially toxic and abundant in the bay, including silver, cadmium, aluminum, manganese, zinc, mercury, and the highly toxic methyl mercury.

“I’m testing for metals to try to figure out the ecology of the population and their habitat utilization and possible health effects, especially in relation to diet found in the bay,” said Komoroske, who has conducted more than 25 habitat sampling excursions.

While in years past the sea turtle data were mainly derived by observing the animals and measuring their growth, today minute blood and shell samplings speak volumes and allow scientists to follow live individuals through time.

“This collaboration allows me to combine all of the elements to characterize the habitats and population health effects of sea turtles living in an urbanized coastal environment,” said Komoroske.

Komoroske intends to complete the analysis in three months and publish the findings thereafter.

The project is funded by the Port of San Diego, SDSU (Rebecca Lewison’s Laboratory), NOAA Southwest Fisheries Sciences Center, Edna Bailey Sussman Foundation, PADI Foundation, and Southern California Academy of Sciences.

-- Mario C. Aguilera