Benthic macrofaunal structure in the intertidal and subtidal of a sandy beach of Southern Brazil

Abstract

Macrofaunal community of a beach were studied from February 1992 to March 1993, in Parana State, southern Brazil. Sample stations were distributed along a transect from the upper sub-aerial beach, to nearly 3 m deep, in the sub-aqueous beach. Three biological samples were obtained in each station with an iron core of 0,05 m 2 surface area, taken to a depth of 20 cm. One sand sample was collected at each station for standard mechanical-sieving grain size analysis. Subtidal samples were collected by scuba diving. Slope of the beach, water table profile, water salinity and temperature in the surf zone and wave height and period were measured each sample month. The dimensionless fall velocity parameter (?) and the surf scaling parameter (?) were computed for a morphodynamic characterization. The beach presented intermediate morphodynamic state only during some spring and summer months, being dissipative in the remainder months. The surf zone presented always a high dissipation. Macrofaunal abundance showed a clear seasonal variation, with highest values during winter for intertidal stations and spring for subtidal stations. Species richness showed few variations for intertidal stations, but a great variation for the subtidal station. Zonation pattems obtained from classification partially fitted to Salvat's physical zones for the intertidal, with saturation and surf zone zones showing a close identity. The result suggests that zonation in sandy beaches is related to sediment stability, instead of strictly tide water levels. A high variable environment in the surf zone was related to a greater variation in species composition.