THE IMPACT OF A SMALL, ALIEN INVERTEBRATE ON A SUB-ANTARCTIC TERRESTRIAL ECOSYSTEM - LIMNOPHYES-MINIMUS (DIPTERA, CHIRONOMIDAE) AT MARION-ISLAND

Density and biomass of the larvae of a small, alien chironomid midge, Limnophyes mininus, whose parthenogenetic adult females do not feed, w ere quantified for ten major lowland plant communities at sub-Antarcti c Marion Island (46 degrees 52'S 37 degrees 51'E) and compared with th e density and biomass of indigenous macro-invertebrates in the same co mmunities. An estimate of litter consumption by larvae of this midge w as also made. L. minimus reached high densities in most of the plant c ommunities sampled, with the highest density being recorded in the Cot ula plumosa biotically influenced community (annual mean of 4,365 indi viduals m(-2)) and the lowest in the Crassula moschata salt spray comm unity (annual mean of 41 individuals m(-2)). Estimates of litter inges tion indicated that L. minimus larvae are capable of consuming between 0.07 and 8.54 g((dry mass)) m(-2) per year, depending on the communit y. In some communities this litter consumption amounted to an order of magnitude more than that consumed by Pringleophaga marioni (Lepidopte ra, Tineidae). Although the larvae of this moth species are thought to represent the bottleneck to nutrient recycling on the island, this st udy showed that midge larvae may also contribute substantially to this process. As a consequence, the considerable changes that have been pr edicted to occur in Marion Island's terrestrial ecosystem as a consequ ence of enhanced predation by mice on P. marioni larvae may be retarde d or obscured by the contribution of the midge larvae to nutrient cycl ing. Hence, it is suggested that greater attention be given to the sma ll and inconspicuous elements of the alien sub-Antarctic faunas becaus e such species may have profound consequences for ecosystem functionin g on these islands.