The swimming rhythm of the sand beach isopod Eurydice pulchra

Eurydice pulchra is shown to have an endogenously controlled swimming rhythm of tidal frequency; in the laboratory this is expressed by animals kept in sea water alone but not by animals given sand, from which they rarely emerge.

Abstract

Eurydice pulchra is shown to have an endogenously controlled swimming rhythm of tidal frequency; in the laboratory this is expressed by animals kept in sea water alone but not by animals given sand, from which they rarely emerge. On the beach the animals evidently rely on being washed from the sand by the rising tide, the endogenous component of the rhythm ensuring that they swim for up to 5–6 h before reburrowing in the sand in a restricted zone between M.T.L. and H.W.N. The rhythm is synchronized by wave action and reinforced by variations in hydrostatic pressure. The number swimming is affected by light, fewer animals swimming by day since well fed animals are photonegative and reburrow immediately they emerge into the surf.