Biodynamics of Particle Processing in Bivalve Molluscs: Models, Data, and Future Directions

Previous models of particle feeding have focused on optimal solutions for particle acquisition or absorption. We propose two conceptual approaches to treat particle feeders as an integrated system of compartments, in hopes of understanding critical limiting factors that might be overlooked by focusing on only one part. The compartment model treats a particle feeder as a series of structures that process particles, with characteristic residence times within compartments and transfer points between them. These might change with overall particle food value and proportion of poor particles. As a non-exclusive alternative, the pathway model considers particle transfer as being analogous to enzyme control systems, with feedback loops that may involve interactions such as negative feedback between compartments that engage in no direct transfer. We examine these models in the light of some studies of particle handling by the deposit-feeding bivalves Yoldia limatula, Macoma secta, and M. nasuta, and the suspension-feeding oyster Crassostrea gigas. In Y. limatula, palp overloading results in feedback that shuts down the particle-collecting palp proboscis. In Macoma, nearly all particles are rejected, suggesting that rejection is necessary because digestion and gut residence time are limiting factors. We suggest that a whole-system approach is important in understanding particle processing by deposit feeders and suspension feeders.