EFFECTS OF AN OIL-SPILL ON THE SOFT-BOTTOM MACROFAUNA OF ARTHUR HARBOR, ANTARCTICA COMPARED WITH LONG-TERM NATURAL CHANGE

The macroinfauna at depths of 30-115 m was sampled in March-April 1989 , c. two months after an oil spill that resulted from the grounding of the Bahia Paraiso. Stations consisted of the oil-spill site and a com parable control location, and two historical sites previously sampled in 1971. The historical sites were located at two distinct points alon g a known continuum of increasing physical stability with depth, attri buted to disturbances from glacial calving. Macroinfaunal assemblages at most stations were characterized by very high densities and numbers of taxa. There were no significant differences (P<0.05) between the o il-spill and control sites in numbers of individuals, species, or fami lies; nor were there any major differences in dominant fauna or overal l community composition. The absence of a detectable impact on the fau na is consistent with results of hydrocarbon analyses, which showed th at subtidal sediments were nearly devoid of contamination emanating fr om the Bahia Paraiso. The assemblage at the shallower of the two histo rical sites, however, showed a substantial change over the 18-yr perio d between studies. This change consisted of a shift toward a more spec ies-rich and abundant macroinfauna characteristic of the more physical ly stable parts of the harbour. This change may be related to the fact that the glacier face near this site has retreated c. 250 m over the last 20 yrs, resulting in less physical disturbance of the adjacent se afloor.