Abstract

The physico-chemical characteristics of the sediment, the nutritional value and the biochemical composition of the sedimentary organic matter and the structure of macroinfaunal assemblages were studied in three sites of the low intertidal of Pelluco, a tidal flat located on the inland coast of the Nord-Patagonic archipelago, southern Chile. The Site 1 was dominated by the razor clam Tagelus dombeii; Site 2 was dominated by the razor clam Tagelus dombeii and the bivalves Diplodonta inconspicua and Semele solida; while Site 3 had no bivalves at all. The site without bivalves showed a stronger decrease in depth of the redox potential than the sites with bivalves. This result was probably related to the process of bivalve reworking which redistributes reduced compounds from deeper layers to the sediment surface. Sedimentological differences and differences in the macroinfauna structure among sites were noticed. Thus the sediment characteristics of deeper strata were more different at the site without bivalves as compared to deeper strata of sites 1 and 2. The total number and the total abundance of the macroinfauna were higher at site 1 and 2. The results of BIO-ENV routine showed that the highest fit between the macroinfauna structure and sedimentological variables, was reached with two and four variables (total carbon and redox, pw = 0.391 and carbohydrates, total nitrogen, total carbon and redox, pw = 0.385, respectively), suggesting that that pattern was closely related to the presence of bivalves which would promote macroinfaunal assemblages throughout biogenic reworking of sediments.