Flora and Fauna of Northwest Florida

Biology Department

University of West Florida

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Salt Marsh Molluscs

Ribbed or Saltmarsh Mussels, Geukensia demissus, are found in and among the roots of the salt marsh plants, embedded in the peat of the marsh surface. Like other mussels, they secure themselves by byssal threads seen extending out from the shell. Because of the anaerobic, chemically reduced environment in which they live, their shell is often chemically eroded on the surface, as seen here.

These mussels are filter feeders, opening their shells and filtering food particles out of the water as incoming tides flood the salt marsh. Although humans do not find them palatable, raccoons love them, and the marsh surface is usually littered with their shells.

Saltmarsh Periwinkles, Littorina irrorata, are pulmanate snails, meaning they are capable of breathing air. They feed on microalgae and detritus on surfaces (aufwuchs) of marsh plants and the marsh peat, scraping the slime layers with horn-like teeth (a radula). These snails are commonly found on the stems of the marsh plants where they climb to avoid the high temperatures and low oxygen of the marsh peat surface, and to avoid their primary predators, Blue Crabs (Calinectes sapidus). Evidence of predation pressure by crabs is seen as broken edges of the shell opening and irregularities from repair of broken edges, where the crabs have tried to crush the shells. Snails that are not so lucky end up as shell fragments on the marsh surface and lunch for the crabs.

 

Olive Nerites, Neritima reclivata, are also common in salt marshes, but are found in the subtidal habitats of shallow flats and in the marsh creeks.