Digestive kinematics of suspension-feeding bivalves: Modeling and measuring particle-processing in the gut of Potamocorbula amurensis

Abstract

Particle digestion in lamellibranch bivalves is partitioned between 2 paths, an 'intestinal' path through the stomach and intestine and a 'glandular' path through the stomach, digestive gland and intestine. In the Asian clam Potamocorbula amurensis (Schrenck, 1867), the relative importance of the intestinal path increases compared to the glandular path as food availability and ingestion rate increases. The effects of changes in food availability and ingestion rate on digestive partitioning are at least as important as the effect of changes in diet observed by other investigators. Analyses of residence-time distributions of inert 9 and 44 μm particle tracers show that the gut of P. amurensis can be modeled as an ideal mixing reactor (stomach and digestive gland) and an ideal plug-flow reactor (intestine) in series. This model appears to be valid for the processing of particles ≤9 μm in size. For particles of ≥15 μm, the ideal mixing component of the model must be modified to account for channeling of particles through the stomach to the intestine. Larger particles can enter the digestive gland, but are probably not phagocytized for intracellular digestion. Instead they may clog the ducts and tubules, limiting phagocytosis of smaller particles and potentially reducing the extent of digestion and absorption. Mixing, and the resultant intragut particle-sorting thus appear to be necessary components of a digestive strategy that incorporates intracellular digestion.