Heavy metals in seawater, marine sediments and corals from the Townsville section, Great Barrier Reef Marine Park, Queensland

The capacity of corals to assimilate heavy metals in response to environmental availability, as defined by sediment and water concentrations, was investigated at three sites in the Townsville region: a harbour (Townsville Harbour), a control (Orpheus Island), and a site occasionally influenced by harbour dredge spoils (Magnetic Island). In Townsville Harbour, biologically available lead, copper, and zinc concentrations were higher than at other sites. Nickel and chromium concentrations were also higher in harbour sediments, but only in phases relatively inaccessible to biota. Skeletal records corresponded with environmental availability of some metals. Goniastrea aspera from the harbour accumulated high lead, copper, and zinc concentrations, relative to G. aspera from Orpheus Island. Nickel concentrations in G. aspera corresponded with ambient available concentrations in sediments from the harbour and Orpheus Island. However, nickel concentrations in Pocillopora damicornis from Magnetic Island did not correspond with ambient available concentrations measured in sediments from this site and Orpheus Island. In some situations, metal availability represented by skeletal records may have been inadequately represented by sediment data; cadmium and chromium concentrations were high in skeletons of harbour G. aspera, but intersite differences were not evident in sediment. Copper and zinc concentrations were high in skeletons of P. damicornis at Magnetic Island, but supporting evidence in sediments was absent. Tissues did not always correspond with environmental metal loads measured in sediments or skeletons. G. aspera tissues recorded high copper and zinc availability in the harbour, but not high lead availability. Furthermore, cadmium, nickel, and chromium concentrations in G. aspera tissues were lower in the harbour than at Orpheus Island, contrasting with skeleton and sediment data. P. damicornis tissues indicated similar metal availability at Magnetic Island and Orpheus Island, which corresponded with intersite comparisons using sediment data, but not with skeleton data that indicated differences. Different tissue/skeleton ratios of metal concentrations in corals from the harbour versus the control site indicate tissue-regulation of cadmium, lead, zinc, and chromium. The study indicates that coral skeletons represent environmental metal loads more faithfully than tissues, but nevertheless coral tissues appear useful for bioassaying a limited range of metals. (C) 2000 Elsevier Science B.V. All rights reserved.