The Orientation of Barnacles to Water Currents

Abstract

Adult populations of Balanus balanoides, B. crenatus, and Elminius modestus are orientated by water current so that the majority have carinae pointing away from current source and cirral net facing the current. Naturally occurring populations of Coronula diadema take up the same orientation in respect of flow of water past the whale host on which they are found. Cypris usually orients first towards light. This orientation is then modified by water currents during growth. Since light generally falls vertically and current flows horizontally, barnacles slowly rotate from a predominantly vertical position when young to a tilted or nearly horizontal position when adult. Orientation of barnacles on hulls of moored craft can usually be explained by dual influence of light and current. There is no appreciable influence of water currents on cypris at time of fixation or during metamorphosis. Current influences orientation throughout growth of metamorphosed barnacle, and its effect is greatest in early stages of growth.