Introduction
Suspension-feeding animals are ubiquitous in aquatic ecosystems, and all major taxa have members for whom suspension feeding is the main foraging mode. Suspension feeders are often the chief primary consumers in aquatic systems but, because of the diverse nature of the particles they collect, they also contribute significantly via their effects as both secondary consumers and detritivores (Gili & Coma, 1998; Jørgensen, 1966). In removing particulate food from the surrounding water, suspension-feeding organisms act as mediators of energy flux between the photic zone and the deep sea, between continental waters and the benthic zone, and between local systems in freshwaters (Gili & Coma, 1998; Wildish & Kristmanson, 1997; Wotton, 1994). Their role in energy transfer means that they are key components of aquatic ecosystems, representing important pathways for energy flow, and are crucial determinants of the productivity of aquatic environments.
Suspension feeders are characterized by the possession of an organ used to capture suspended particles from the water (feeding structure). The feeding structures utilized by suspension feeders are highly variable, and include appendages bearing hairs, mucus or silk nets, gill rakers and baleen plates, lophophores, tentacles, and ciliated and flagellated cells. Within a feeding structure, individual collecting elements are the first point of contact for food particles. Transport of particles (particle flux) to the feeding structure is achieved by the flow of water, provided either by active pumping or by external flow.