What habitats contain the greatest numbers of horseshoe crabs?

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Horseshoe crab (Limulus polyphemus) with a hard, rounded shell and long pointed tail lying on sandy ground. — horseshoe crab Horseshoe crab (*Limulus polyphemus*).

Horseshoe crabs are most abundant in estuarine waters. Specifically, the Delaware Bay—an estuary located between Delaware and New Jersey—is home to the world’s largest population of these animals.12

These marine arthropods rely on sandy beaches within these estuarine environments for spawning, typically during high spring tides in the spring and summer months. While they are found along the east coasts of Asia and North America, their reliance on these specific coastal habitats makes them vulnerable to environmental changes, such as beachfront property development and habitat loss, which have contributed to population declines in certain regions like New England.12