Responses of crustacean larvae to hydrostatic pressure: Behavioral basis of high barokinesis

Abstract

Most crustacean larvae show a progressive increase in mean swimming speed upon stimulation with larger increases in hydrostatic pressure (high barokinesis). This response contributes to the ascent response upon a pressure increase and is part of a depth regulatory negative feedback system. High barokinesis could result (1) if swimming speed is graded according to the magnitude or rate of the pressure increase or (2) if larvae have two swimming speeds, a slow unstimulated rate and a fixed faster stimulated rate. In the second case, mean swimming changes as the proportion of larvae in each swimming mode changes. The present study was undertaken to differentiate between these alternatives. Video records of Stages I and IV zoeae of the crabs Rhithropanopeus harrisii and Neopanope sayi upon step increases in pressure were analyzed by computer to determine swimming speed distributions. The first alternative was correct because swimming speed distributions were generally unimodal and the speeds of the greatest n...