Behavioral basis of depth regulation in the larvae of brachyuran crabs

Abstract

A model for behavioral regulation of depth of negatively buoyant zooplankters is used as the basis for discussion of research on depth regulation by brachyuran larvae.Behavioral responses to conservative environmental stimuli modify the effects of negatlve buoyancy.Basic distribution patterns which result may be further modified by responses to increasingly more variable stimuli.Techniques and experimental results for orientation responses to gravity and light are reviewed, as are kinesis responses to light, temperature, salinity, and hydrostatic pressure.Other modifying regulators such as endogenous rhythms in locomotor activity, starvation, and pollutants are discussed.A summary of results by stimulus is provided.Negative geotaxis and high barokinesis promote upward migration in first stage larvae of most species.Ontogenetic changes in sign of geotaxis and presence of barokinesis result in less precise depth regulation and thus vertical scattering in later zoeal stages.Megalopae regain behavioral traits which yield precision in depth regulation.The tactic contributes to dispersal by early stages and recruitment to favorable adult habitats by later instars.Implementation of the model in experimental systems is discussed and its utility in the study of dispersal and recruitment tactics in brachyurans is described, using examples from the literature.