Community structure of intertidal boulder-cobble fields in the Straits of Magellan, Chile

Abstract

Based on quantitative samples taken along 4 transects in mobile hard-bottom intertidal areas of the Canal Whiteside, Magellan region, biotic composition, abundance and distribution patterns are described. The intertidal substrates, mainly formed by boulders and cobbles, represent highly heterogenous habitats from the structural point of view, and demonstrated a species richness higher than previously mentioned in some preliminary reports. Community structure parameters (abundance, species richness, diversity, and evenness) were not homogenous in the study areas, suggesting local dynamics. Differences in the vertical distribution of organisms were also found, suggesting changes of the zonation pattern along the beach profile. The macrofaunal assemblages were dominated by few species, with different specific compositions between transects. In general, representatives of Mollusca (Mytilus chilensis, Perumytilus purpuratus), Polychaeta (Hemipodus simplex), and Amphipoda (Paramoera fissicauda, P. brachyura, Transorchestia chilensis) were the numerically dominant groups. In terms of biomass, molluscs were highly dominant, mainly M. chilensis and P. purpuratus. Among the macroalgae, rhodophytes were the group with the highest presence, but Ulva lactuca (Chlorophyta) was the dominant species. In the upper sandy terrace, no macroorganisms were found. Several species found at Canal Whiteside have a wide circumpolar distribution in Sub-Antarctic regions.