The Behaviour of the Stalked Intertidal Barnacle Pollicipes polymerus J. B. Sowerby, with Special Reference to its Ecology and Distribution

Abstract

The stalked barnacle occurs often in dense masses in the exposed midlittoral of the American West Coast. The animals are orientated on the rocks so that the cirral net faces the rush of water after the waves have broken and as they pour over the rocks and boulders. The orientation appears to be mediated through the cirri; comparison is made with the twisting movements of operculate barnacles. Activity to nondirectional currents is discussed; a certain level of current flow or turbulence is required before normal feeding activity begins. The spat, which settles largely on the peduncles of adults, is orientated within the pits formed by the calcereous scales. Spontaneous activity of valves and peduncle is demonstrated. The former consists of opening and closing movements and the latter of bending, contraction and expansion. This inherent activity occurs in air and water. The animals grow very slowly some of the largest individuals may be 20 years old. Maturity is only reached after 5 years. It is shown that the specialized behaviour allows the species to maintain itself in a restricted part of the intertidal zone against competition from faster-growing animals that mature quickly and produce large broods of young.