The Presence of Juvenile Horseshoe Crabs, Limulus Polyphemus, and Other Benthic Fauna of Mid-Atlantic Coastal Bays

Douglas C. MillerThe Inland Bays of Delaware, Rehoboth Bay, Indian River Bay, and Little Assawoman Bay, serve as spawning grounds for the Atlantic horseshoe crab, Limulus polyphemus. While nearby Delaware Bay is known for remarkably high horseshoe crab abundances, there have been few investigations of spawning activity and the ecology of juvenile horseshoe crabs in the Inland Bays. Using a suction dredge, evidence of juvenile horseshoe crabs and other benthic organisms was collected from Indian River Bay in September and October of 2011. A juvenile horseshoe crab in the trilobite stage, three embryos, five juvenile molts, and 65 horseshoe crab egg shell fragments were found. In addition, benthic fauna representing nine phyla were collected. Seventeen species of arthropods were identified and found to be the most abundant group collected. The amphipods Listriella barnardi and Jassa marmorea were the most abundant organisms in nearly all samples. Molluscs were also well-represented, with seven species in lower abundances than the arthropods. Several sample sites contained highly similar assemblages. Evenness and overall diversity were high at most sites. In addition to horseshoe crab eggs and the trilobite larvae, many of the organisms collected by the suction dredge were similar in size to early juvenile horseshoe crabs, thus providing additional confirmation that the suction dredge is an effective sampling device for juvenile horseshoe crabs. Data from this study corroborates earlier studies of benthic organism abundance in the Inland Bays, and will be used to guide future juvenile horseshoe crab sampling efforts.Marine Scienc