ARE PLANKTONIC LARVAE OF MARINE BENTHIC INVERTEBRATES TOO SCARCE TO COMPETE WITHIN SPECIES

Several models for the evolution of complex life histories have assume d a carrying capacity for both larval and postlarval stages. In additi on, the densities of larvae in laboratory experiments are often so hig h that there is competition for food. Published values for maximal cle arance rates and estimated abundances of larvae suggest that these ass umptions and experimental conditions are unrealistic for most marine l arvae. For most ciliated larvae, maximum clearance rates are at most a few mi of water daily, and their estimated larval concentrations are at most one to several larvae per liter. Therefore these larvae appear to be too scarce for their grazing to affect their food supply. Larva e of most species are also scarce relative to co-occurring planktonic animals that feed on particles in the same size range. Larvae of many species are scarce relative to co-occurring larvae with a similar feed ing apparatus. These observations suggest that larvae of most species have a negligible effect on their food supply. Exceptions could occur when a single species of larva dominates the zooplankton; such circums tances appear to be rare, although extreme aggregations of larvae domi nated by a single species could be missed by pump or net samples. Anal ogous but more conjectural arguments can be made for density-dependent attraction of predators to larval prey. These inferences apply to sin gle species, not to meroplanktonic larvae as a whole: in some coastal waters, larvae of benthic invertebrates comprise a large portion of th e multicellular planktonic animals. Also, a species' larval growth may be food-limited in many waters, even when the abundance of food is in dependent of the abundance of its larvae.