The effects of dredge-spoil dumping on a shallow water soft-sediment community in the Solitary Islands Marine Park, NSW, Australia

In December 1999, 28000 m(3) of sediment was dredged from two sites within the harbour at Coffs Harbour. NSW. Dredging was carried out using a trailin g suction hopper-dredge which transported the spoil to a shallow (6 m) site within the adjacent Solitary Islands Marine Park for disposal. Evaluation of the effects of the dredge-spoil dumping at the receiving site was conduc ted by taking replicated van Veen grab samples at the disposal site and at two control sites, before, immediately after, and three months after dumpin g. The results indicated that dredge-spoil dumping had no detectable effect on either the structure of the invertebrate community or the physical char acteristics of sediment at the receiving site. Although there were some sig nificant faunistic differences between samples from the disposal site and t he control sites immediately following dumping, these were related to preex isting differences between sites rather than to the effects of dredge-spoil disposal. Four principal factors are likely to have contributed to the lac k of impact: (i) dredged material had similar sedimentary characteristics t o those at the receiving site; (ii) dredged material was free from contamin ants:, (iii) the disposal method systematically distributed a number of sha llow layers of sediment over the disposal site and thus motile macrofauna h ad the opportunity to migrate upwards between passes of the barge; and (iv) the disposal site was in a high energy environment where the resident biot a are likely to be adapted to namic sedimentary conditions. The lack of det ectable effects suggests that the disposal strategy was one which minimized impacts within an area which has high conservation value and should thus b e adopted as a model for future works within the region. (C) 2001 Elsevier Science Ltd. All rights reserved.