[The effect of hydrostatic pressure on the swimming activity of three hyponeustonic crustacea, Anomalocera patersoni, Pontella mediterranea, Labidocera wollastoni (Copepoda, Pontellidea)].

The three species A. patersoni, P. mediterranea, L. wollastoni, were found to show a marked response to pressure changes, swimming upwards with increased pressure and downwards with decreased pressure. Endogenous rhythm of activity tended to disappear in specimens maintained under constant pressure conditions equivalent to 20 meters depth. But circadian exogenous rhythm is more clearly determined with Pontellids submitted both to constant pressure (2 bar) and diurnal changes in light intensity than with Pontellids kept under normal pressure. Perception of little changes in hydrostatic pressure is perhaps used by hyponeustonic species to help in depth regulation.