Mollusks and the Environment

Mollusks and the Environment. . Shells are made by mollusks. A shell is the main source of protection from predators and the environment. There are more than 300 species of mollusks living in the shallow waters around Sanibel and Captiva Islands. These mollusks can be found living in a number of different habitats, including the muddy areas, bear mangrove stands oyster reefs, sandy beaches, piles and wharves, and others. From the standpoint of the food they eat, theses mollusks can be divided into a number of different categories. , Some mollusks, like limpets, turbans, and top snails, are herbivores, grazing on seaweeds r microscopic marine plants (algae)., Other mollusks are predators, feeding on marine invertebrates, including other mollusks. Crown conchs tulips, lightning and other whelks, and the horse conch are predators. The horse conch is the top predator in local molluscan communities, eating mostly other large molluscan such as tulips and lightning whelks., Most bivalves (clams, cockles, oysters, mussels, pen shells, etc.) are filter-feeders, taking in large amounts of water and retaining micro-algae, their preferred food. A small number of gastropods, such as slipper and worm snails are also filter-feeders. In the calm waters of Pine Island Sound and San Carlos Bay near Sanibel, the main filter-feeders are oysters. An individual oyster may filter hundreds of gallons of seawater each day. In addition, oysters form reefs that provide habitat, food and shelter for larger number of organisms. Oyster reefs are indicators of the health of the surrounding environment., . The Cayenne keyhole limpet, Diodora cayenensis, like most limpets graze on algae. , Photo by Amy Tripp, . The giant cockle Dinocardium robustum, the stiff pen shell, Atrina rigid and the bay scallop, Argopecten gibbus, are filter-feeders. , Photo by Amy Tripp except for scallops by Joyce Matthys, . The horse conch, Triplofusus giganteus, eating a lighting whelk, Busycon sinistrum. Horse conchs are the top predators among area mollusks. , Photo by Joyce Matthys, . Crown conchs, Melongena corona, feed on wide variety of prey, including small crabs. , Photo by Amy Tripp, . Lightning whelks, Busycon sinistrum, feed on bivalves such mussels. , Photo by Amy Tripp