Comparing the Development and Viability of Horseshoe Crab Eggs Laid in Beach and Salt Marsh Habitats

The horseshoe crab, <i>Limulus polyphemus</i>, has recently been found to spawn regularly in salt marshes, despite the long-held assumption that salt marsh sediments are not conducive for embryonic development. Here, we tested the prediction that eggs laid in the salt marsh would develop more slowly and be less viable than eggs laid on beaches. We flagged the nests of spawning horseshoe crabs in the marshes and beaches of three states-South Carolina, Connecticut, and New Hampshire-and then excavated those nests one or three weeks later. We staged the excavated embryos to compare developmental progress between marshes and beaches. We found that, in general, habitat type did not affect embryonic development rate or the viability of embryos; instead, temperatures experienced by embryos drove most developmental patterns. Horseshoe crabs also buried their eggs in the marsh at shallower depths than at the beach, possibly to avoid deleterious conditions found deeper in marsh sediments. These results indicate that salt marshes are viable habitats for horseshoe crab recruitment and should be considered for the proper management and conservation of this species.