Cross-shore Mysidacea (Crustacea) distribution in two sandy beaches with contrasting morphodynamics

Abstract

The order Mysidacea comprises small and very common crustaceans that inhabit most coastal ecosystem. The present contribution describes the composition, abundance and distribution of mysids in two sandy beaches representing the extreme conditions of the morphodynamics spectrum. Six species of mysids were found at the studied beaches. Metamysidopsis neritica Bond-Buckup & Tavares, 1992 was the most abundant species with more than 97% of the total individuals collected at the two beaches. At the dissipative beach was dominant in the swash and surf zone, with the greater abundance in the inner surf zone. At the reflective beach, this species was extremely abundant in the surf zone and backward the breaker. Bowmaniella brasiliensis Bacescu, 1968 occurred in low density at the surf zone of the dissipative beach, with the greater abundance in the outer surf zone, and it was practically absent in the nearshore zone. We suggest that mysids zonation in sandy beaches may be first developed as a response to food availability patterns imposed by the nearshore circulation systems, and in the second place as a result of competitive exclusion. The suggestion of partitioning of food and spatial resources shown by the mysid species is surprising in view of the apparent physical harshness and low spatial heterogeneity that seem to characterise the beach environment.