Study of macroinvertebrate in two intertidal soft bottoms: reference data in conditions of incipient anthropic impact

Abstract

In this study, we analyzed the relation between the abundance of benthic macroinvertebrates and relevant environmental variables in two intertidal in Golfo Nuevo (Argentinean patagonia), one near a urban center (Mimosa Beach, PM) and the other at 20 km from that location (Cerro Avanzado Beach, CA). Within each beach, the environmental conditions were homogeneous (90% of similarity). Mean size grain values, anoxic layer depth, and percent organic matter were 117.6 µm, 4.95 cm and 0.76%, and 165.2 µm, 9.5 cm and 0.63%, for PM and CA respectively. Even though three families were the most abundant in both beaches (Tellinidae, Maldanidae and Opheliidae), nine families were exclusively observed in PM. This resulted in a higher biodiversity in PM (3.06) in relation to CA (1.77). When faunal composition was considered, the similarity between sites was notably low (lower than 82%) if compared with the environmental conditions. Granulometry and organic matter were the variables with the highest correlation with macroinvertebrates abundance. This is the first study of macroinvertebrates and their relationship with some environmental variables throughout the complete spatial extension of two beaches in Golfo Nuevo. This is of particular relevance if we consider that coastal regions of this gulf has been exposed to a sustained increase of anthropic activities in the last years and base- line information is scarce.