Two large ribbed mussels (Geukensia demissa) are shown here protruding about halfway out of the sediment at low tide. Their lower ends are glued to rhizomes of smooth cordgrass by their byssal threads, to help them escape being pulled out of the mud and broken (e.g., by racoons). Ribbed mussels are one of the few bivalves that can effectively collect bacterioplankters and eat them; most bivalves (e.g., clams) depend on phytoplankton for food, and can't collect bacterioplankton. Ribbed mussels are so good at collecting planktonic microbes and suspended clay, that they can cause opaque flood-tide water moving onto the marsh to become visibly clear within several minutes. The activities of the mussels cause an increase in the productivity of the bacterioplankton. See Newell & Krambeck, 1995, Responses of bacterioplankton to tidal inundations of a saltmarsh in a flume and adjacent mussel enclosures, J Exp Mar Biol Ecol 190:79-95; Newell & Porter, 2000, pp. 159-185, in Weinstein & Kreeger, Concepts and Controversies in Tidal Marsh Ecology, Kluwer.