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.

Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

“…Cancer pagurus Linnaeus, 1758, Carcinus maenas, Macropipus spp. (Sulkin 1984), and the first larval stage of Galathea strigosa (Linnaeus, 1761) and Galathea dispersa (Bate, 1859) reached maximum swimming speeds of approximately 2 cm s (1 (Foxon 1934).…”

Larval dispersion along an axially symmetric mid-ocean ridge

“…Larvae of species living in shallow water exhibit a variety of behaviors that result in stratification of their populations in the water column (Forward, 1988;Sulkin, 1984;Young and Chia, 1987).…”

Larval Biology of the CrabRhithropanopeus harrisii(Gould): A Synthesis

“…The rates of change in these environmental factors induce behavioral responses that are consistent with the negative feedback model (Sulkin, 1984). Thus, studies using step changes in environmental factors will not indicate the sensory thresholds for detection or the minimum gradients that can be perceived, but they will indicate the behavioral responses involved in the negative feedback system for depth regulation.…”

“…Studies with R. harrisii larvae agree with the model because step changes in environmental factors encountered upon descending-such as an increase in pressure (Wheeler and Epifanio, 1978;Forward and Wellins, 1989), a decrease in temperature (Ott and Forward, 1976), and an increase in salinity (Latz and Forward, 1977)-induce an ascent. In addition, R. harrisii zoeae show a dramatic increase in swimming speed, termed high barokinesis (Sulkin, 1984), upon a step pressure increase (Bentley and Sulkin, 1977;Forward and Wellins, 1989;Forward, 1990a), which is a common response among crustacean larvae (Sulkin, 1973(Sulkin, , 1984. Alternatively, changes that occur upon ascendingsuch as a decrease in pressure (Wheeler and Epifanio, 1978;Forward and Wellins, 1989), an increase in temperature (Ott and Forward, 1976), and a decrease in salinity (Latz and Forward, 1977)-induce a descent.…”

“…Ascents occur upon a positive phototaxis; negative geotaxis and activity increase with the opposite responses, resulting in a descent. As proposed by Sulkin (1984) for crab larvae, zooplankton have a negative feedback system associated with these environmental factors and behavioral responses. The general model is that exposures to environmental conditions that occur upon ascending (temperature increase, salinity decrease, and pressure decrease) induce downward movement due to negative phototaxis, positive geotaxis, and activity decrease.…”