Has jarosite dumping at a deepwater site off eastern Tasmania, Australia, had a measurable effect on the midwater zooplankton and micronekton communities?

The biomass, abundance, species diversity and length-frequency distribution of macrozooplankton and micronekton at a deep-ocean dumpsite southeast of Tasmania, Australia, were compared with those of the surrounding water mass es. The dumping of jarosite - a waste product of zinc refining that contain s trace quantities of heavy metals - began in 1973. The dumpsite, which typ ically receives 170,000 tonnes of jarosite per annum, is in an oceanographi cally, and biologically, dynamic area. Depending on season and large-scale oceanographic effects, the dumpsite can be dominated by high-salinity, warm waters of subtropical origin or low-salinity, cool waters of subantarctic origin. The comparisons of the macrozooplankton and micronekton parameters between water masses, and between the two years of the study (1992, 1993), did not show any changes that could be attributed to the jarosite dumping. Micronekton abundance was significantly lower over the dumpsite in 1992; ho wever, this appears to be due to the presence of a warm-core eddy in the re gion of the dumpsite in that year. Changes in the regional oceanography bet ween years also appear to account for significantly greater micronekton bio mass over the dumpsite in 1993.