Particle processing and gut kinematics of planktotrophic bivalve larvae

Abstract

Although the clearance rates of planktotrophic bivalve larvae have been widely reported, post-oral particle processing is less well understood. Using a series of exposures to differently colored fluorescent polystyrene microbeads, we quantify several post-oral process in the larval gut, including gut fullness, gut passage time, and degree of mixing by modeling larval guts as a continuously stirred tank reactor (CSTR), plug flow reactor (PFR) or combinations of the two in series. We also varied several experimental conditions to understand how these affected estimates of gut kinematic parameters. We found the larval guts of M. galloprovincialis aged 2 and 7 days post-fertilization, had gut exchange time >1 h and were best described either as a CSTR or CSTR in series with a PFR. Mixing stomach contents likely aids post-oral particle selection, physical breakdown of ingested material, and accelerates the diffusion of digestive enzymes in the gut volume. Reactor models also provided estimates of ingestion rates, which were compared to those obtained by other authors who measured rates of bead accumulation. In accordance with reactor theory, ingestion rates were negatively and nonlinearly correlated with gut passage times and positively related to maximal gut fullness. Collectively, these studies provide new insight on the digestive strategy of planktotrophic bivalve larvae.