Abstract
A commercially available enzyme immunoassay (EIA #K052, Arbor Assays, Ann Arbor, MI) was validated (parallelism and accuracy) for measurement of plasma aldosterone in endangered Kemp’s ridley (Lepidochelys kempii) and leatherback (Dermochelys coriacea) sea turtles.
Using the validated assay, archived frozen Kemp’s ridley plasma samples (n=218, representing 137 individuals) were analyzed, including turtles that were naturally cold-stunned (n=97), turtles exposed to oil during the Deepwater Horizon spill (n=60), and apparently healthy free-ranging turtles captured by in-water methods (manual capture, n=21; trawler capture, n=40). Circulating aldosterone was elevated in Kemp’s ridleys affected by natural and anthropogenic stressors (p<0.001), with the highest levels found in turtles exposed to oil (549±65 pg/ml) and trawler capture (523±42 pg/ml). Cold-stunned turtles had elevated aldosterone levels upon admission to the hospital (136±29 pg/mL), and then levels declined with convalescence (18±4 pg/ml) (p<0.001). Lowest concentrations were found among rehabilitated, cold stunned turtles that were deemed healthy for release to the wild (11±3 pg/mL).
Archived frozen leatherback plasma samples (n=60, representing 56 individuals) were analyzed, including turtles entangled in fishing gear (n=6), stranded on land (n=11), apparently healthy free-ranging turtles sampled after hoop-net capture for ecological research (n=13), and apparently healthy nesting females sampled on land (n=30). Aldosterone concentrations were lower in nesting females compared to all other circumstances (23±3 pg/ml) (p<0.001). Significantly higher aldosterone levels were measured in entangled turtles (156±42 pg/ml), followed by stranded turtles (274±52 pg/ml), with the highest concentrations recorded in apparently healthy leatherback turtles that were captured by hoop-net (457±147 pg/ml) (p<0.05).
Aldosterone was positively correlated with corticosterone in both species, and was positively correlated with sodium concentrations in leatherbacks and cold-stunned Kemp’s ridleys. Aldosterone tended to be higher in Kemp’s ridleys that were persistently hypernatremic, although not statistically significantly. Unexpectedly, aldosterone was positively correlated with plasma potassium concentrations in both species. Aldosterone was negatively correlated with thyroid hormone concentrations (free T4) in both species. Aldosterone also correlated (positively or negatively) with several other plasma analytes, including ionized calcium, ionized magnesium, chloride, lactate, blood urea nitrogen.
The novel aldosterone data produced in this study were biologically sensible in comparison to past studies of this hormone in other reptile species, including limited data for Kemp’s ridley turtles.1-4 These results confirm that aldosterone is released as part of the adrenal physiologic stress response in Kemp’s ridley and leatherback sea turtles. Release of aldosterone under the influence of stressors could contribute to the physiologic derangements that are sometimes observed in ill or injured sea turtles (e.g., hypernatremia). Results of this study provide an additional analyte that can be used for assessment of health of these endangered species; and possibly an additional therapeutic angle for the rehabilitation of injured and ill individuals.
Acknowledgments
We thank Morris Animal Foundation for funding this study. The success of this study relied upon samples, data, and effort that were contributed by many sea turtle conservation, rescue, and rehabilitation programs. We especially thank Cody Mott, Justin Perrault, Jennifer Keene, Brian Stacy, Craig Harms, Nicole Stacy, Kristen Hart, as well as the staff and volunteers of Audubon Nature Institute, Massachusetts Audubon Wellfleet Bay Wildlife Sanctuary, Center for Coastal Studies, and New England Aquarium, especially Scott Landry, Robert Prescott, Karen Dourdeville, Adam Kennedy, Deana Edmunds, Jeff Powalisz, Margaret Phan, and Tanya Nanthakijjar. All activities and samples described herein were conducted with authorization of the United States Fish and Wildlife Service and National Oceanic and Atmospheric Administration. Permit and IACUC details for each realm of this work are available upon request.
*Presenting author
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