A new explanation of particle capture in suspension- feeding bivalve molluscs

Abstract

Using video endoscopy, we examined water flow through the infrabranchial cavity and observed particle capture by the ctenidia (gills) of several species of suspension-feeding bivalve molluscs. We found that previously published interpretations of the particle capture process did not adequately explain our in vivo observations. Instead, we propose that particle capture in bivalves can be explained in terms of hydrosol filtration theories that have been shown to apply to a wide diversity of aquatic suspension feeders. Particles are captured by direct interception with the ctenidial filament and then transported along the frontal surface of the filament by mucociliary processes. Two primary mechanisms aid in capture. First, the low angle at which particles approach the filaments increases the probability of encounter with frontal cilia. Second, vortical flow patterns set up by the beating of the laterofrontal cilia or cirri reduce or block flow through the interfilamentary spaces and redirect it toward the frontal surface of a filament. This flow pattern further increases encounter efficiency with the frontal cilia and promotes particle retention on the frontal surface. Our studies indicate that the suspension-feeding complex as a whole (incurrent siphon/margin, ctenidia, and mantle) functions in a highly integrated manner and is critical for particle capture. This observation calls into question previous explanations developed from examination of surgically altered bivalves.

Particle capture mechanisms in suspension-feeding invertebrates

“…Particles > 4 µm are stopped and transferred to the frontal side, whereas smaller particles either follow the flow around the cirri or they are stopped by the cirri's branching cilia (Dral 1967, Moore 1971, Owen 1974, Jørgensen 1975b, 1996, Owen & McCrae 1976, Silvester & Sleigh 1984, Riisgård 1988, Beninger et al 1992, Nielsen et al 1993, Riisgård et al 1996, Silverman et al 1999. Although a mechanism based on a low particle-approach angle and direct interception at gill filaments has been proposed (Ward 1996, Ward et al 1998, this does not appear consistent with the principles of fluid dyamics (Beninger 2000, Silverman et al 2000. Based on estimates of pressure drop for flow through a laterofrontal-cirri screen (modeled as parallel cylinders of diameter 0.06 µm and spacing 1.3 µm) and creeping flow calculations, Riisgård et al (1996) found it plausible that during normal beating Larsen & Riisgård (1994) of the laterofrontal cirri the through-current passes mainly around the laterofrontal cirri in an oscillatory, unsteady, 3-dimensional pattern and that only a little flow may leak through the branching cilia.…”

Marine aggregates facilitate ingestion of nanoparticles by suspension-feeding bivalves

“…These two species possess ctenidia with a unique combination of architecture and complexity of laterofrontal (LF) ciliary tracts, which aid in particle capture (Ward et al 1998). Mussels (ca.…”

Effect of oysters Crassostrea virginica and bottom shear velocity on benthic-pelagic coupling and estuarine water quality

“…Previous studies of bivalve ecological functions have ranged from highly controllable laboratory studies with short response times and no feedback loops (e.g. Wright et al 1982, Swanberg 1991, O'Riordan et al 1993, Ward et al 1998, to experiments in field flumes (Asmus et al 1992(Asmus et al , 1998, to very realistic but largely uncontrollable whole-ecosystem field studies (e.g. Dame & Libes 1993) that include all the direct and indirect interactions and feedbacks.…”