The influence of upwelling variation on the spatially-structured euphausiid community off central-southern Chile in 2007-2008

This study assesses the spatial and temporal patterns of the euphausiid community from the coastal upwelling zone and oceanic areas of central-southern Chile, surveyed between August 2007 and November 2008. A total of 22 species were found, most of them already described for the region. The numerically dominant species was Euphausia mucronata for the entire study area (>60%), which was found in more oceanic waters (>90°W), thereby expanding its longitudinal distribution range. The species showed distinct spatial distribution patterns, allowing its classification as a coastal, oceanic, southern and northern species. The community descriptors - species richness, total abundance, Pielou and Shannon index - all had patterns associated with the cross-shelf and alongshore axes. Over a temporal scale, species abundance and community descriptors showed strong seasonal patterns. Abundances decreased offshore but diversity increased towards the oceanic area, revealing an inverse relationship between total abundance and the Shannon index. Diversity was positively related to sea surface temperature. Although the most abundant species were concentrated within the coastal zone, euphausiid abundance and diversity in the oceanic region were high. Our findings suggest that the high productivity of the upwelling region may sustain the euphausiid populations in the coastal transition zone and in the offshore region, and that high abundance and diversity across the entire region may be maintained by a highly heterogeneous environment promoted by upwelling, giving rise to an increased number of potential ecological niches.