NHT/NAP FINAL REPORT ECOLOGICAL STATUS OF THE DERWENT AND HUON ESTUARIES Catriona Macleod and Fay Helidoniotis November 2005 NHT/NAP Project No. 46928 National Library of Australia Cataloguing-in-Publication Entry Macleod, Catriona (Catriona K.). Ecological status of the Derwent and Huon estuaries. Bibliography. Includes index. ISBN 1 86295 287 6. 1. Estuarine health - Tasmania - Derwent River Estuary. 2. Estuarine health - Tasmania - Huon River Estuary. 3. Estuarine pollution - Tasmania - Derwent River Estuary. 4. Estuarine pollution - Tasmania - Huon River Estuary. 5. Ecological surveys - Tasmania. 6. Derwent River Estuary (Tas.). 7. Huon River Estuary (Tas.). I. Helidoniotis, F. II. Natural Heritage Trust (Australia). III. National Action Plan for Salinity and Water Quality (Australia). IV. Tasmanian Aquaculture and Fisheries Institute. Marine Research Laboratories. V. Title. 577.78609946 Published by the Marine Research Laboratories- Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Private Bag 49, Hobart, Tasmania 7001. E-mail: [email protected] Ph. (03) 6227 7277 Fax (03) 6227 8035 The opinions expressed in this report are those of the author/s and are not necessarily those of the Tasmanian Aquaculture and Fisheries Institute. Copyright protects this publication. Except for purposes permitted by the Copyright Act, reproduction by whatever means is prohibited without the prior written permission of the Tasmanian Aquaculture and Fisheries Institute. © Tasmanian Aquaculture and Fisheries Institute, University of Tasmania 2005. NHT/NAP FINAL REPORT ECOLOGICAL STATUS OF THE DERWENT AND HUON ESTUARIES Catriona Macleod and Fay Helidoniotis November 2005 NHT/NAP Project No. 46928 Tasmanian Aquaculture and Fisheries Institute Marine Research Laboratories Biological status of the Derwent and Huon Estuaries Biological status of the Derwent and Huon Estuaries Catriona Macleod and Fay Helidoniotis Executive Summary This study was undertaken to fill a significant gap in our understanding of the system ecology of the two main estuaries in southern Tasmania and to provide baseline information to assist in the ongoing management of these systems. The Derwent and Huon estuaries are similar in their biogeographical, climatic and physical characteristics but differ markedly in their levels of industrialisation. The Derwent estuary is highly impacted with several major industrial and urban contamination sources throughout its catchment. Heavy metals in particular, represent a considerable threat to the system. In contrast the Huon estuary is largely unimpacted, finfish aquaculture being the only major industry affecting the system, although there is potential for future development and industrialisation. Both the Derwent and the Huon estuaries are strongly depositional with the majority of the estuary composed of soft sediments. These sediments will act as a repository for any contaminants to the system and the benthic infauna will in turn reflect the cumulative effects of these pollutants. There is considerable information on the various anthropogenic loadings to the Derwent and on the effects of these on water quality, but prior to this study there was very little information on the biological consequences of these contaminants. Information on the benthic ecology is an essential pre-requisite to any effective management strategy. Accordingly, in order to determine the overall impact in the estuary or to evaluate future remediation, baseline information on the current biological condition of the system was essential. This study undertook a broad assessment of the ecological changes in both estuaries. Extensive spatial sampling was undertaken throughout the estuaries in order to characterise the benthic communities. These communities were then evaluated in relation to the changes in the natural environmental conditions as well as changes in the level of organic enrichment and metal contamination. Infaunal samples in the Derwent were taken at 55 sites which coincided with sediment sampling previously undertaken by the Department of Primary Industry, Water and Environment (DPIWE) for analysis of sediment composition, metal contamination levels and organic carbon content. In the Huon a further 25 infaunal samples were collected from sites selected to give a broad overview of the ecology of the system. Sediment samples were also collected from the Huon for sediment particle size analysis, and evaluation of metal levels and organic carbon content. NHT/NAP Final Report – Page 1 Biological status of the Derwent and Huon Estuaries The results of this study found that there were similarities in the pattern of community distribution along the estuaries. In neither system were there any areas where fauna was completely absent, in fact diversity was high throughout most of the sample sites. The faunal community in both estuaries was most strongly related to the natural geomorphology and salinity gradient of the estuaries, and in turn to the depositional character of the system and the organic content. Changes throughout the estuaries were gradual but several discrete communities were identified within each estuary and the species which most strongly characterised these communities are described. The community distribution in the Derwent was slightly more complex than the Huon, as in addition to the natural gradient there were also multiple anthropogenic gradients. Prior to this study it was anticipated that the extremely high concentrations of metals throughout the Derwent would be the most significant structuring influence on the ecology of the system. However, the results show that metal contamination was not the overriding determinant of benthic infaunal community composition, although both organic enrichment and metal contamination had a significant influence on the community structure in localised areas. Contrary to our expectations, areas with very high metal concentrations, including areas containing toxic metals (i.e. mercury and arsenic), had an abundant fauna which suggests that somehow these metals were not biologically available. This raises an interesting question regarding how the infauna avoid this toxicity. The metals may be chemically bound in the sediments or perhaps the infauna are actively circumventing any toxic effects by avoiding, compartmentalising or excreting the metals. If the toxicity is managed through biochemical stabilisation of the sediments then any changes in the sediment chemistry of the estuary could have a serious and detrimental effect. On the other hand if the toxicants are being stabilised within the animals then this represents a significant bioaccumulation risk through the food chain. This study shows that the Huon is a relevant and valuable biological reference point for comparison with the Derwent and consequently can provide useful parameters for developing management guidelines for both the Derwent and Huon. The biological information provides an important resource for researchers and managers. It represents a baseline ecological reference for any future assessment of sediment condition and ecological status. The study defines species indicative of communities characterising particular regions within the system. These biological zonation patterns will enable environmental managers to locate biologically relevant monitoring sites and to evaluate improvements and deterioration in the estuarine condition both spatially and temporally. Invasive species are considered to be one of the most significant threats to global biodiversity. Prior to this study it was well known that there were several key introduced species in the Derwent, particularly around the port of Hobart, but the distribution of species throughout the rest of the system or in the Huon estuary was largely unknown. This study mapped the current status of invasive species in both estuaries providing a point of reference to monitor and manage their spread and distribution. Examination of the environmental preferences of these species suggests that in general their environmental tolerances are broad and that range extension is more likely to result from opportunity and reduction in competitive pressure rather than any particular environmental preference. This has significant implications for the management of these ecologically and potentially economically important species. NHT/NAP Final Report - Page 2 Biological status of the Derwent and Huon Estuaries Although this study was specifically focussed on the Derwent and Huon estuaries, the findings can be applied in a much broader spatial context. Comparison of the faunal information for the lower estuary regions with other local studies suggests that the community characterisation would be applicable to other estuaries in south-eastern Tasmania. The general response of the main species and infaunal community groups to metal contamination could potentially be applicable throughout southern temperate Australia, whilst the functional community response and invasive species information has even wider application. NHT/NAP Final Report – Page 3 Biological status of the Derwent and Huon Estuaries Table of Contents EXECUTIVE SUMMARY.......................................................................................................................1 1. INTRODUCTION .............................................................................................................5 1.1 BACKGROUND ......................................................................................................................5