Shellfish include mussels, cockles, periwinkles, clams, and oysters. Giant clams, green mussels and oysters support edible shellfishery. Clam chowder may be prepared with fresh, steamed clams or canned clams. Clam chowder is any of several chowder soups containing clams and broth. These are primarily associated with bivalve molluscs, such as mussels, clams, oysters and scallops. Clams that do not respond to the spawning of neighboring clams may be reproductively inactive. Their diets include clams and oysters, arthropods, small fish and gastropod molluscs. The bacterial mats provide nourishment for mussels, clams, limpets and sea snails. The class has 30,000 species, including scallops, clams, oysters and mussels. Other species including salmon, shrimp, lobster, clams, squid and crab, are also commercially fished. Ingredients may include mushrooms, potatoes, seaweed, onion, shrimp, fish, clams, and sliced daikon. Singaporeans also enjoy a wide variety of seafood including crabs, clams, squid, and oysters. Sea otters eat shellfish and other invertebrates (especially clams, abalone, and sea urchins). Tide pools provide a home for hardy organisms such as starfish, mussels and clams. The Chesapeake Bay is host to many species, including blue crabs, clams, oysters, and rockfish.