The ontogeny of barokinesis during the zoeal development of the xanthid crabRhithropanopeus harrisii(Gould)†

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Abstract
The presence and significance of change in behavioral response to hydrostatic pressure is examined during the zoeal development of the xanthid crab Rhithropanopeus harrisii. Mean swimming speed is measured for each zoeal stage at several pressure increments. Larvae of all four stages which exhibit positive phototaxis show high barokinesis at pressures between ambient and 60 cmHg pressure increment. Some stage 2 zoeae were negatively phototactic and exhibited low barokinesis. At all pressures, mean swimming speed increases with succeeding zoeal stages. Swimming speeds of stage 2 larvae exhibiting negative phototaxis are higher than those measured when larvae are positively phototactic. These results are discussed in terms of depth regulation of the larvae and in terms of other results previously reported in the literature.