Pulse Disturbances to the Colonization of Hard-substrates and in situ Determination of Copper using Diffusive Gradients in Thin-films (DGT): Quantifying Dose and Response in the Field

Abstract

Studies conducted in Port Philip Bay, Victoria, Australia are described that examined the effect of experimentally elevated copper concentrations on the recruitment of epifauna to settlement plates. Simultaneous measurement of the copper concentration using diffusive gradients in thin films (DGT) allowed direct comparisons to be made between the labile copper concentration measured at the settlement surface, and the biological effects observed. Copper concentrations created by the field dosing technique were between 20 – 30 μg l⁻¹ for the first 2 d, but then dropped considerably for the following 4 d (3 μg l⁻¹), and were indistinguishable from background for the final 7 d. The first 2 d of a copper pulse reduced the recruitment of barnacles, ascidians, serpulid worms, an encrusting bryozoan, and didemnid ascidians. The impacts occurred despite the copper pulse being much less than published LC₅₀ values for similar species. The impacts were no longer obvious by day 7 or 14, having been obscured by either high mortality of early settlers, or large settlement events that took place after day 2. Thus the greatest impact of the pollution event occurred during the period of highest toxicant concentration. The value of this study lies in the correlation of toxicity effects with bio-available metal concentrations under realistic (natural, in situ) conditions.

Keywords:

• copper
• pulse
• DGT
• field experiment
• sessile invertebrates
• recruitment

Acknowledgements

We are grateful to H Zhang for help and advice on the application of the DGT technique, to the Port of Melbourne Authority and Department of Defence for access to Piers, and John Lewis (Australian Defense, Science and Technology Organisation) for providing Breakwater Pier water quality data. We thank I Hamilton, J Hindell, L Morris, J Sherwood and H Zhang for helpful discussion and criticism of earlier versions of this manuscript. The DGT equipment and trace metal analyses were financed through a generous award from the Australian Federation of University Women. Emma Johnston and Angus Webb were supported by Australian Government Postgraduate Awards (APA). Angus Webb was also supported by a CSIRO Division of Marine Research Supplementary PhD Award.