Faunal response to morphology and water circulation of a sandy beach with cusps

Abstract

Morphology of, and water circulation on, a reflective microtidal beach with 26 to 32 m cusps are described. The distribution of meiofauna, macrofauna, zooplankton and fishes was quantified and related to features such as cusp horns and bays, and rip currents. Meiofauna avoided the horn and concentrated on the sides of the rip current running down the cusp bay, although different taxa were concentrated at different intertidal levels. Macrofauna filter feeders, 2 donacid bivalves, were concentrated in cusp bays and showed no tidal migrations. A hippid crab, which is a scavenger, occurred throughout the cusp system and exhibited tidal migrations. Zooplankton, dominated by amphipods and mysids, was more abundant inside the 'surf zone' than outside. Within the surf zone it showed a weak tendency to concentrate off cusp horns. Fishes were netted in highest numbers around rip heads in cusp bays, and were less abundant in the surf off cusp horns. The reasons for these distribution patterns are discussed.