Spatial distribution of peracarids in the intertidal zone of the Ria Formosa (Portugal)

The aim of the present study was to contribute to the knowledge of the poorly studied peracaridan community in the Ria Formosa system. The Ria Formosa is the most important wet region at the southern coast of Portugal. Benthic macrofauna samples and some environmental parameters were collected fortnightly at three sampling sites, from November 1990 to December 1991, in the intertidal zone. At each site, samples were taken during low tide, at five equidistant levels between high and low water. Results of numerical analysis indicated that distinct peracaridan groupings were associated with different sites and levels. Cluster and ordination analysis of the three sites indicated similarities among the highest level samples. The lowest level samples revealed greater dissimilarity. Furthermore, the temporal and spatial distribution of the most abundant peracaridan species indicated the existence of biological relationships between these and their relationship to environmental factors. Thus, Cyathura carinata dominated the upper areas with the more stable food sources, related to finer sediments, all year around. During spring and summer the tanaid Apseudes latreillii was the dominant species, reaching high densities in the lower areas.