Colonization of soft sediments by benthic communities: An experimental approach in Admiralty Bay, King George Island

In order to understand nearshore biological community colonization following impact events that affect the distribution and occurrence of species and subsequent recovery a manipulative experiment was set up in King George Island. This work aimed to study colonization patterns of benthic macrofauna in defaunated soft sediment, comparing them with occurrence patterns of macrofaunal benthic organisms found in the natural soft sediment of adjacent areas, in shallow waters of Admiralty Bay, King George Island, Antarctic Peninsula. For this, a manipulative field experiment was installed through SCUBA diving at 22 m depth in front of the Antarctic Brazilian Station. Samples of defaunated and natural soft-sediments were analyzed. Defaunated soft sediment in plastic boxes (a = 0.02 m2) were deployed in the seabed and examined after 6, 12 or 18 months. Natural soft-sediment collected with cylindrical corers of 10 cm in diameter (a = 0.08 m2), in adjacent areas at the experiment installation and during the changing and removal of the experimental boxes, were also analyzed. Altogether, 20,680 organisms belonging to 6 phyla among 42 species were identified. Thirty three taxa out of the 42 recorded were common in both natural and defaunated sediment types, 6 taxa occurred only in natural sediment and 3 taxa only in defaunated sediment. The most abundant groups throughout the experiment were: Oligochaeta, Polychaeta, Bivalvia, Gastropoda and Crustacea. In the natural sediment a total of 10 species were considered Constant, 8 species Accessory, 21 species Accidental. In the defaunated sediment 14 species were Constant, 4 species Accessory, 18 species Accidental. Analysis of variance indicated significant differences in total abundance and in Torodrilus sp. abundance in the periods of 6 and 18 months, and MDS analysis showed a clear separation between natural and defaunated treatments. Torodilus sp. was the taxon with the highest relative contribution (26%) in natural sediment. In the defaunated sediment treatments, the most common taxa were cumacean Leuconidae morphotype 1 (19%) and the bivalve Yoldia eightsi (Couthouy, 1839) (18%). The statistical results indicated significant differences between the natural and defaunated treatments with respect to benthic macrofaunal associations. Species richness and abundance in defaunated treatment were less than in natural treatment. The results suggest that recovery levels in Antarctic waters after events of defaunation are very low and in order to be of value experiments may need to be for longer periods.