The concept of hydrodynamic limitation of macrobenthic animal populations arose from an attempt to explain the importance of flow to benthic populations consisting of two key trophic groups: the deposit and suspension feeders (Wildish 1977). Consistent with the aims outlined in Chapter 1, we are concerned primarily with the latter trophic group, and deposit feeding macrofauna are not dealt with in detail here.

We will first consider the historical background of the benthic limitation by flow concept, as well as a special theory associated with it: trophic group mutual exclusion, and hypotheses derived from the latter. We present turbulent mass transfer models relating seston supply and uptake by populations of suspension feeders with both field and laboratory experiments to test the theory. We also present field evidence that suspension feeding populations can be impoverished by high energy water movement events. For completeness, we briefly consider two possible competing theories of trophic group mutual exclusion which propose that biotic interactions between deposit and suspension feeders explain the exclusion of one of the groups.

Benthic limitation by flow

The concept to which the general theory of benthic limitation by flow belongs is that of limiting factors (Wildish 1977). Limiting factor theory has a long history, beginning with Liebeg's (1840) law of the minimum (see in Odum 1971) and Blackman's (1905) ideas on optima and limiting factors.