The estuary is one of the most productive habitats on earth, with its phytoplankton, eelgrass beds and salt marshes. In the Great South Bay, that means home for a variety of sea life. Detritus from the marshes is washed into the bay, where it is used as food by many organisms, including mollusks and crustaceans.
The sandy beaches within the intertidal zone support algae, bacteria, and a few species of worms and small crustaceans.
Crustaceans include crabs, shrimp, copepods, isopods, and other invertebrates with a hard exoskeleton.
One economically important shellfish in the waters surrounding Fire Island is the blue crab (Callinectus sapidus). Other crabs include the lady crab (Ovalipes ocellatus), green crab (Carcinus maenas), and spider crab (Libinia emarginata).
Ghost crabs (Ocypode sp.) dig their burrows on the beach, while mole crabs (Emerita talpoida) live in the swash zone along the edge of the ocean. The horseshoe crab is not a crustacean, but in a class of its own, more closely related to spiders.
Other crustaceans include the sand shrimp (Crangon septemspinos), and grass shrimp (Palaemonetes vulgaris).