Daily and Tidal Components in the Persistent Rhythmic Activity of the Crab, Sesarma

Abstract

IN intertidal organisms the rates at which various physiological functions proceed are often related to the state of the tide. In a habitat in which environmental conditions change so drastically with the ebb and flow of the tidal waters, this is not particularly surprising. What is remarkable is that the rate of many of these functions continues to vacillate in approximate synchrony with the tide when organisms are removed to non-tidal, constant conditions in the laboratory. These persistent vacillations are referred to as tidal or bimodal lunar day rhythms. By way of example, persistent tidal rhythms have been described for oxygen consumption in crabs¹; vertical migrations of planarians² and diatoms³; colour change in crabs⁴; spontaneous activity in crabs^5,6, amphipods^7,8, and fish⁹; and filtration rate in mussels¹⁰.