Monitoring the impact of human activities in Admiralty Bay, King George Island, Antarctica: isotopic analysis of c and n in the summer of 2005/2006

Stable isotopic analyses have been used for assessing anthropogenic influence in marine communities. The variation of stable C and N isotope signatures in sources of organic matter and in benthic invertebrates were investigated at Martel Inlet nearshore zone, during the summer of 2005/2006, to attend a monitoring program. Water, sediment and invertebrates of different trophic types (suspensivore, depositivore, grazer and carnivore) were sampled at the intertidal and subtidal zones (up to 25 m) off the Brazilian Antarctic Station Comandante Ferraz (CF) in two periods of the summer. As a reference area, Ullmann Point (UP) was sampled in the same way. Off CF, the δ13C values for consumers ranged from –23.92 (Laternula elliptica) to –12.34‰ (Nacella concinna) in Nov/2005, and from –23.36 to –12.73‰ (L. elliptica and Yoldia eightsi, respectively) in Feb/2006. Some δ13C values were more enriched in CF in February when compared to November, mostly for POM and sediment. This result was not observed in Ullmann Point and suggested an influence of the sewage organic matter in the coastal area near the Brazilian Station, mainly at the beginning of summer. The δ15N values for sources and consumers did not differ significantly between areas or periods.