EFFECTS OF THE NELLA-DAN OIL-SPILL ON THE FAUNA OF DURVILLAEA-ANTARCTICA HOLDFASTS

The effects of a small spill of light marine diesel on the community s tructure of invertebrates inhabiting Durvillaea antarctica holdfasts w ere examined for samples taken from sites which received heavy, modera te and no oiling at Macquarie Island, sub-Antarctic. Non-metric multid imensional scaling (MDS) at both the species and a mixed taxonomic lev el separated samples collected at oiled sites from the controls. Pre-i mpact data were only available for 1 of the heavily oiled sites and th ese samples grouped with those from control sites in MDS analysis. Hol dfasts from oiled sites were characterised by heavy sediment loads, a dominance of capitellid, cirratulid and spionid polychaetes and the ra rity of the isopod Limnoria stephenseni. In contrast, samples from the control sites were dominated by peracarid crustaceans and in particul ar by the herbivorous isopod L. stephenseni. Analysis of differences i n the size distribution patterns of the 4 most common species (the iso pod L. stephenseni, the amphipods Parawaldeckia kidderi and Hyale nova ezealandiae and the gastropod Laevilittorina caliginosa) suggests that impacts occurred across all sizes for L. stephenseni and P. kidderi. At the heavily oiled sites, size distribution patterns for the gastrop od L. caliginosa were skewed towards larger individuals, suggesting a differential mortality of smaller individuals. We suggest that the rar ity of L. stephenseni at the oiled sites may result in the accumulatio n of sediment within the internal chambers of the holdfast, producing a habitat more suitable for polychaete worms. The residual levels of h ydrocarbons within these sediments may further restrict the polychaete species to opportunistic taxa which were not found at the control sit es. As this study did not include pre-impact sampling, the interpretat ion of the results is partially confounded with possible, unmeasured, pre-existing site-specific differences in the community structure. Whi le the availability of pre-impact data from 1 oiled site (from an earl ier study) has strengthened interpretation with respect to possible oi l effects, further sampling of the sites is needed to resolve some of these uncertainties.