Abstract

The loggerhead sea turtle (Caretta caretta) is one of 7 species of living sea turtles, and one of four species endemic to the waters of South Carolina.¹ 25-hydroxyvitamin D is an important hormone for the regulation of calcium and phosphorous across many animal species, and has been shown to be abnormal in green sea turtles (Chelonia mydas) being rehabilitated in the Southeastern United States.^2,3 However, while calcium phosphorous derangements are commonly observed in stranded loggerhead sea turtles (personal observation), no normal serum 25-hydroxyvitamin D levels have been reported in this species. Here we report the normal serum 25-hydroxyvitamin D from 21 wild, apparently healthy loggerhead sea turtles captured along the coast of South Carolina. We also compare the 25-hydroxyvitamin D of these healthy turtles with 42 rehabilitated loggerhead sea turtles from a rehabilitation facility along the coast of South Carolina. Rehabilitation animals had 8 different primary causes of stranding: debilitated turtle syndrome (DTS; n=19), 4 trauma (boat strike, predator attack, or stingray barb; n=12), hook and line fisherman interaction (n=3), entanglement in gear (n=2), cold stun animal transferred from another facility (n=2), gastrointestinal impaction (n=1), suspected nutritional secondary hyperparathyroidism (n=1), or unknown cause of injury (n=2). Healthy wild turtles had a median 25-hydroxyvitamin D level of 22 nmol/L, and a 10th to 90th percentile range of 14 to 31 nmol/L. Intake values were statistically significantly different across groups (p=0.042), but release 25-hydroxyvitamin D values were not (p=0.16). Statistically significant differences at intake were observed between control and DTS animals (p=0.0034) and control and trauma animals (p=0.0016), but not between DTS and trauma animals (p=0.23). No other statistically significant differences were found between groups, likely due to all other groups having three or fewer animals. Median and 10th to 90th percentile values (percentiles only calculated for groups with n>2 turtles) at the time of intake are listed below in table 1. Based on these findings we would recommend taking steps to supplement 25-hydroxyvitamin D level in loggerhead sea turtles undergoing rehabilitation through diet and exposure to UVB light, particularly in patients suffering from DTS or trauma.

Table 1. Statistical summary of median, 10th percentile, and 90th percentile serum 25-hydroxyvitamin D levels from wild and rehabilitated loggerhead sea turtles at intake and release

Acknowledgements

The authors would like to thank Willow Melamet, Cait Crosby, Katelyn McGlothlin, Mackenzie Polk, the many interns and volunteers of the South Carolina Aquarium Sea Turtle Care Center, and the staff and volunteers of the South Carolina Department of Natural Resources for their incredible hard work on the rehabilitated sea turtles in this study.

*Presenting author

Literature Cited

1.  South Carolina Department of Natural Resources. 2018. http://www.dnr.sc.gov/marine/pub/seascience/seaturtle.html. Accessed October 25, 2018.

2.  Stringer EM, Harms CA, Beasley JF, Anderson ET. 2010. Comparison of ionized calcium, parathyroid hormone, and 25-hydroxyvitamin D in rehabilitating and healthy wild green sea turtles (Chelonia mydas). J Herp Med Surg 20:122–127.

3.  Purgley H, Jewell J, Deacon JE, Winokur RM, Tripoli VM. 2009. Vitamin D3 in captive green sea turtles (Chelonia mydas). Chelonian Conserv Biol 8:161–167.

4.  Stacy NI, Lynch JM, Arndt MD, Avens L, McNeill JB, Cray C, Day RD, Harms CA, Lee AM, Peden-Adams MM, Thorvalson K, Segars AL, Norton TM. 2018. Chronic debilitation in stranded loggerhead sea turtles (Caretta caretta) in the southeastern United States: Morphometrics and clinicopathological findings. PLoS One 13: e0200355. https://doi.org/ 10.1371/journal.pone.0200355