Mechanisms Of Particle Retention and Selection in Suspension-Feeding Bivalves

Suspension-feeding bivalve molluscs are among the most important groups of benthic organisms in coastal ecosystems, and have evolved a highly effective mucociliary feeding mechanism to process the particulate material to which they are exposed. These selective capabilities are well documented, but the underlying mechanisms remain undefined. This thesis assessed pre- and post-capture particle processes to better understand passive and active selection mechanisms of bivalves. Several questions were posited, including: 1) How do physicochemical interactions affect particle capture and selection; 2) Why are some particles more likely to be rejected or ingested than others; and 3) Is a chemosensory response mechanism involved? Using flow-through chambers and natural suspended matter, capture efficiency (CE) of blue mussels (Mytilus edulis) was determined seasonally over a one-year period. Polystyrene microspheres of known size were used to verify size-specific capture. Results demonstrate that particles \u3e 4µm are captured with ~100% efficiency, and no evidence was found of bivalves adjusting either feeding behavior or physiology over time. Flow-through chambers were also used to study post-capture selection of mussels and oysters (Crassostrea virginica) exposed to microalgae whose surface-property profiles (surface charge, wettability, and surface sugars) were determined. Algae were delivered to bivalves in pairs, and rejection and preferential ingestion outcomes used to develop statistical models and examine which surface properties determined selection. Multiple regression models identified specific surface sugars and wettability as the strongest predictors of particle selection, explaining ~90% of the variability in selection for mussels and ~94% for oysters. In vitro studies with characterized microspheres and microalgae demonstrated that distinct surface properties interacted variably with bivalve mucus, resulting in differential adherence of particles and in some cases capture by mussels. Finally, effects of microalgae metabolites on particle capture and transport were examined using assays with excised gills and in vivo endoscopic examinations. Results demonstrated that addition of metabolites had no effect on transport, indicating an active chemosensory response does not affect selection. Findings outlined in this thesis further demonstrate that specific physicochemical properties of particles, and their interactions with mucus in the pallial organs mediate a passive particle selection mechanism in bivalves