Bay Critter Profile: The Horseshoe Crab

The arrival of spring marks the return of thousands of horseshoe crabs (Limilus polyphemus) from deep ocean waters to our local bays. Often referred to as “living fossils,” horseshoe crabs are arthropods that date back 360 million years. Their presence is most obvious during the months of May and June, when males and females engage in their annual mating and nesting rituals. During spring tides, female crabs crawl out of the bay to lay thousands of tiny green eggs in the wet sands of the tideline. The eggs serve as an important food source for over 20 different species of shorebirds. After a few weeks, the eggs hatch into tiny larvae which swash back into the bay and crawl to the bottom. The larvae are an important component of the estuarine food web, serving as a food source for various finish and crabs in the estuary. In addition, adult horseshoe crabs have demonstrated their medical value in human cancer research, as an extract of their blood cells can detect the presence of endotoxins in human blood serum.

The horseshoe crab population is under enormous pressure from over-fishing due to the use as eel and conch bait, as well as from the increasing loss of nesting habitat due to bulkheading and dredging. Like every critter in the bay, they shouldn’t be taken for granted.