In this chapter, our concern is primarily with the first filtration stage of feeding as defined later. In the next chapter, we deal with the second stage of suspension feeding, which involves the mechanisms of particle capture on the appropriate surface. Because these two stages of feeding are the only ones directly affected by flow, they are the only ones considered in physiological detail in this book.

Background

In suspension-feeding animals, feeding and growth involves a series of coordinated steps. Each of these steps is dependent on the preceding one (Table 4.1). We will refer to suspension feeding as inclusive of the first four steps shown and reserve the term filtration for the first two only. Filtration or clearance rates (see Chap. 2, the section, Initial feeding responses) need not, therefore, equal feeding rates if particle sorting leads to rejection as pseudofaeces. Growth encompasses the remaining catabolic and anabolic steps. Growth rates need not be directly related to the feeding rate because of differential digestion of sestonic particles. For example, in the giant scallop, some microalgae pass through the gut undigested (Shumway et al. 1985b). Residence times of food in the gut may be increased or decreased (Bricelj, Bass, and Lopez 1984) and thus change the contact time between ingested food, and digestive and absorptive surfaces.