Dense populations of suspension-feeding bivalve molluscs, such as oysters and mussels, play dominant roles in the ecology of coastal ecosystems. Bivalves not only convert heterogenous mixtures of suspended material into animal flesh that can be used by higher trophic levels, but also are one of the strongest interactors in shallow water benthic–pelagic coupling (Dame, 1993a,b, 1996). Through suspension-feeding activities, bivalves can strongly affect pelagic and benthic processes by removal of phytoplankton, deposition of feces and pseudofeces, and cycling of dissolved nutrients to the water column. Tight coupling may lead to stimulation of phytoplankton blooms (Lewin et al., 1975), depletion of phytoplankton (Cloern, 1982; Officer et al., 1982), changes in phytoplankton composition (Baker et al., 1998), or more complex ecosystem level effects (Dame et al., 1984; Newell, 1988; McKee, 2002).

Bivalve molluscs are exposed to a suspended food supply that varies in size, concentration, and quality, over both spatial and temporal scales. The food source includes material supplied directly from the water column or by resuspension events (Frechette et al., 1989; Judge et al., 1993). The way in which bivalves mediate benthic–pelagic processes is complicated by the fact that very few particle feeders are so simple that they merely encounter particles, engulf them, and excrete metabolic end products. Rather, in bivalves there is strong evidence that changes in the content of non-nutritive particles elicit compensatory feeding responses (Bayne et al., 1987, 1993; Iglesias et al., 1992; Barille et al., 1993; Bacon et al., 1998; Hawkins et al., 1998; Cranford and Hill, 1999; Levinton et al., 2002). Studies have also indicated differential handling of particles by bivalve pallial organs (Ward et al., 1997, 1998a) and qualitative selection (Newell and Jordan, 1983; Prins et al., 1991; MacDonald and Ward, 1994; Bougrier et al., 1997; Defossez and Hawkins, 1997; Ward et al., 1998a; Brillant and MacDonald, 2000), even of similar-sized particles (Shumway et al., 1985, 1997; Ward and Targett, 1989; Ward et al., 1997). Therefore, the way in which bivalves deal with the heterogenous mixture of suspended particles could affect the quantity and quality of material that is cycled back to the water column or delivered to the benthos via pseudofeces and feces.