It is the purpose of this chapter to address the second stage of suspension feeding, as defined in Chapter 4: specific particle capture mechanisms at the appropriate suspension-feeding collecting surface. The theory for our approach to this is borrowed from physics and engineering literature, inclusive of sieving and the aerosol theory mechanisms. We are especially indebted to reviews by Rubenstein and Koehl (1977), LaBarbera (1984), and Shimeta and Jumars (1991), which help interpret this in a biological context. We also include a novel mechanism involving hydromechanical shear forces at the bivalve gill proposed by Jørgensen (1981a, 1983, 1990), which is not part of the classical particle capture theory. Other topics discussed here include the nature of seston, how sestonic particles reach the collector, and a brief consideration of those species where calculations of seston encounter efficiencies according to aerosol theory have been made.

Nature of seston

The type of particles which may be collected by suspension feeders are highly variable and dependent on the local conditions. Non-viable particles of silt, clay, sand, and detritus may be processed for the attached microbiota. Viable particles include bacteria, phytoplankton, invertebrate larvae, and eggs, many of which are weakly motile. Collectively, this material is referred to as seston (Fig. 5.1); it ranges in size from less than 1 μm up to 1000 μm or more.