Abstract

Subtidal reef communities from much of the world's coastline have been described in detail, but data from the world's most extensive subantarctic rocky reefs is scarce. The objective was to describe these southern coastal systems and measure the extent to which they vary in terms of fundamental measures of community structure. The Magellan Region constitutes an intermediate site between relatively well-studied temperate regions and Antarctica. Previous studies suggest that dominant canopy species may reflect different disturbance histories and associated communities may similarly be expected to vary structurally. We hypothesized that variation in subtidal sessile assemblages in the Magellan Strait, where Macrocystis pyrifera widely dominates, would be less than at Antarctic sites, where Desmarestia spp. or Himantothallus grandifolius may dominate depending on disturbance regimes. Our results showed that benthic assemblages in the Magellan Strait were similar where physical structure of the reef was similar, but differed strongly where reef form differed. At sites in South Shetland Islands, benthic assemblages differed in terms of dominant macroalgae and sessile community structure; however evidence that the Desmarestia -dominated site was more highly disturbed was equivocal. Shading produced by Macrocystis in Magellan Strait and ice effect in Antarctica are likely strong structuring factors in their respective communities, which would need to be considered when comparing community characteristics.