Abstract

Horseshoe crabs (Limulus polyphemus) are ancient marine arthropods that are commonly exhibited in zoological institutions throughout North America. A large population of male and female horseshoe crabs presented with a history of not-molting. There is very little literature on the nutritional needs of horseshoe crabs in regard to molting, but there is evidence that iodine plays an important role in other invertebrates. A study was performed to evaluate total iodine levels in horseshoe crab hemolymph and the effect of dietary iodine supplementation. Twelve randomly chosen, mixed-sex adult animals from the population were selected for the study, eight were used for supplementation and four were not supplemented. No supplementation had been given to any crabs prior to the study. The supplemented animals were already held on exhibit in an 17,000 L open air enclosure with sand filtration, protein fractionation, and ozone. They were supplemented with 0.7 mg iodine per feed (shrimp injected with Florida Aqua Farm Mineral Mix© mixed with water fed 3 times weekly). Crabs were fed individually, submerged in baskets within the system. The non-supplemented control crabs were housed in an approximately 14,000 L open air enclosure with sand filtration, protein fractionation, and ozone. Prior to the study, control crabs had been housed in a non-ozonated system and were moved to the study system on day 0. Hemolymph was collected from crabs on day 0, 49, and 112. Venipuncture was performed on all animals and approximately 1.5 ml of hemolymph was collected via the arthrodial membrane using a 22-g needle and 3 ml syringe. Hemolymph was collected into cryovials and total iodine was evaluated at Michigan State University Veterinary Diagnostic Laboratory. Water quality parameters were normal in all systems throughout the study. Supplemented crabs had an average total iodine value of 11.6 ng/ml at day 0 and 16.4 ng/ml on day 49 while control crabs had an average total iodine value of 24.8 ng/ml at day 0 and 10 ng/ml on day 49. No molting occurred in both the supplemented and control crabs. Preliminary findings indicate that iodine supplementation may be achieved through supplemented food orally, and ozonated systems may decrease total iodine within horseshoe crabs. Further study is needed to evaluate the complex relationship of iodine within marine systems and its effect on invertebrates and their molting process.

Acknowledgements

The authors thank the husbandry and life support staff of SeaWorld San Diego for their technical assistance.

* Presenting author