PERSPECTIVES ON THE SIZE STRUCTURE OF LACUSTRINE ZOOBENTHOS, ITS CAUSES, AND ITS CONSEQUENCES

Benthic ecologists have recently begun to use animal body size as an alternative or supplement to traditional taxonomic descriptions of benthic communities, probably because of the successful use of a body-size based approach by planktonic ecologists. Relatively little information is available on the size structure of benthic animal communities, factors that affect the size structure of zoobenthic communities, or consequences of the size structure of a zoobenthic community. Marine and lacustrine zoobenthic communities have different size structures, and there are conspicuous differences among lakes in zoobenthic size structure. Factors likely to influence the size structure of lacustrine zoobenthos include water chemistry, lake productivity, and vertebrate predation. I conclude, however, that the effects of vertebrate predation on zoobenthic size structure probably are weaker than on zooplankton owing to the availability of physical refuges to the zoobenthos and to the widespread occurrence of morphological and behavioral defenses against vertebrate predation among zoobenthos. In turn, the size structure of zoobenthos may affect growth rates and productivity of fish, the fate of zoobenthic production, the turnover rate (and similar ecophysiological properties) of zoobenthos, food web efficiencies, and rates of sediment mixing. There are thus many opportunities for zoobenthic ecologists to use a size-based perspective in their research. Nevertheless, benthic ecologists should not apply planktonic paradigms about body size relationships uncritically to benthic communities, for body size has different implications for zoobenthos than for zooplankton.