Abstract

Leatherback turtles (Dermochelys coriacea) that forage seasonally on scyphozoan jellies off the west coast of the United States are part of the critically endangered western Pacific breeding stock that nests in Papua Barat (Indonesia), Papua New Guinea, and the Solomon Islands.^1,2 Critical foraging habitat was recently designated for this declining population along central California, Oregon, and Washington, with prey condition noted as the sole biological feature essential for conservation of the species (final rule, 77 FR 4170, Jan 26, 2012). Although jellies can concentrate trace elements,⁵ their role in the bioaccumulation and trophic transfer of marine biotoxins has not been studied. Domoic acid, a potent marine biotoxin that causes significant morbidity and mortality in marine mammals and seabirds,^6,8 was recently documented for the first time in a dead stranded leatherback turtle in central California.³ To investigate the exposure pathway of domoic acid in the leatherback food web, turtles and their prey were sampled on central California foraging grounds during documented harmful algal bloom (HAB) events in the summer and fall of 2010 and 2011. In addition, samples from three dead juvenile leatherbacks recovered as bycatch from the Pacific Islands region were included. Four species of scyphozoan jellies were sampled: the brown sea nettle (Chrysaora fuscescens; n = 16), moon (Aurelia labiata; n = 5), egg yolk (Phacellophora camtschatica; n = 8), and purple-striped (Chrysaora colorata; n = 4). Plasma, urine, and/or gastrointestinal contents from live captured (n = 2) and dead stranded (n = 4) leatherback turtles were also analyzed for toxin exposure. Domoic acid was found in 94% (31/33) of whole jellies (range: 5–141 ng/g). Three leatherback turtles had low levels of toxin in urine and gastrointestinal samples (< 8 ng/ml or ng/g), likely representative of chronic background exposures. However, one dead stranded adult leatherback, the first tagged animal from a western Pacific nesting beach to be recovered on the U.S. west coast, had high concentrations of domoic acid in the urine (432.9 ng/ml), esophageal contents (327.3 ng/g), and stomach contents (284.8 ng/g), suggesting an acute exposure. These domoic acid levels are comparable with those of other acutely intoxicated species,^6,8 but it is not clear at this point whether the cause of death was associated with toxin ingestion. Further investigations on the risk of domoic acid to this vulnerable population are warranted since both HAB events and jelly blooms appear to be increasing as a result of changing ocean conditions, potentially in response to the cumulative effects of human impact.^4,7

Acknowledgements

Funding for this project was provided by a grant from the NOAA Oceans and Human Health Initiative. The authors wish to thank Jim Harvey, John Douglas, Todd Jones, Scott Hansen, Tomo Eguchi, and Lisa Komoroske for assistance with sample collection in the field. We also acknowledge necropsy support from the staff at the California Department of Fish and Wildlife - Marine Wildlife Veterinary Care and Research Center.

* Presenting author

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