Variation of a polychaete community in nearshore soft bottoms of Admiralty Bay, Antarctica, along austral winter (1999) and summer (2000-2001)

摘要

Studies on community structure of Antarctic benthos are mostly conducted on summer samplings, when ice-impacts and productivity blooms are intense. Few surveys performed during winter demonstrated that, despite temperatures and productivity stability, community structure is variable. In order to assess how polychaete community is influenced by seasonality and depth along a discontinuous year, six replicate samples were taken in nine surveys during winter and four in summer at two depths (12 and 25 m) in Admiralty Bay, King George Island. Spatial patchiness was more intense at 12 m presupposing ice-mediated and wave-induced disturbances, whereas 25-m patchiness among replicates was restricted to summer surveys. A pattern of temporal stability was partially confirmed in 12-m site. Deeper site was characterized by seasonality with dominant-species replacement reflecting shifts in organic matter availability. Diversity was higher in early and midwinter following both summer productivity blooms and macroalgal decomposition that extend the energy budget into the winter, analogous to microbial biomass supply of "food banks" that sustains the benthic ecosystem functions over winter in Antarctic Peninsula shelf deeper areas. Despite the opportunistic status of several nearshore polychaetes, it was possible to distinguish those that responded to organic enrichment (i.e., Capitella perarmata and Ophryotrocha notialis), from those associated with physical disturbances (i.e., Aphelochaeta cincinnatus and Levinsenia gracilis). Awareness of such patterns and their spatial and temporal variations will facilitate future studies on community assessment, especially those based on indicator species of benthic communities.