No abstract

This study examined the short-term recovery response at 2 salmon farms in southern Tasmania where organic loads were equivalent, but where background environmental conditions differed markedly. Although benthic communities at each of the farm locations showed good recovery over the 3 mo fallow period, community structure did not fully return to that observed under reference conditions at either location. At the Stringers Cove site the primary ecological functions of the background community were restored, but this was not the case at Creeses Mistake. These differences in recovery response were a direct reflection of background environmental conditions. Stringers Cove sediments had naturally high organic carbon content and as a result there was greater similarity in the ecological function of the unimpacted and impacted conditions at this location than at Creeses Mistake, where, under unimpacted conditions, the sediments had a very low organic content. In addition, the background fauna at Stringers Cove contained several species with reproductive strategies suited to rapid recruitment and well adapted for early recolonisation in organically enriched sediments. In contrast, the background fauna at Creeses Mistake not only changed more with the impacts of organic enrichment, but was less able to re-establish populations directly by immigration, needing to rely to a greater extent on remediation of the sediments by transitional species before being able to colonise. This has important implications for environmental management, as it suggests that the sediments in some areas have greater resilience to organic inputs.

Marine sediment samples collected from various sites at 2 Atlantic salmon farms in Tasmania were analysed for the presence of Neoparamoeba sp., an amoeba associated with amoebic gill disease (AGD) in farmed Atlantic salmon. Environmental variables of the sediment layer at each site, including redox potential and sulphide concentration, were measured and the general biological condition assessed by video observation. Sediments and environmental data were collected on 4 occasions at each site over a 12 mo period. Neoparamoeba sp. was detected in populations of amoebae recovered by culture from all sites and in 50% of all sediment samples taken. There was evidence of a seasonal influence on the presence of the amoeba, but this was different at each farm. No Neoparamoeba sp. was recovered from any sites at Farm 1 during the winter of 2002 whereas at Farm 2 this was the case for the summer of 2003. There appeared to be no relationship between the presence of Neoparamoeba sp., salmon farming activities and environmental parameters. KEY WORDS: Neoparamoeba · Amoebic gill disease · AGD · Marine sediments · Environmental parametersResale or republication not permitted without written consent of the publisher

A Tasmanian tidalflat receiving differing amounts of vehicle traffic associated with the servicing of oyster farm leases was sampled for sediment properties and benthic community structure. There was a gradient of vehicle usage in both the littoral zone (LZ) and the intertidal zone (IZ), with the highest usage in the intertidal zone equating to the lowest usage in the littoral zone (IZ2=LZ1). Results indicate that the littoral sediments were less compacted where vehicles were present. Species richness and diversity were reduced in the littoral sites (70%) and one intertidal site (50%) where there was vehicle traffic. Multivariate analyses confirmed the univariate findings. Large bivalves and epibenthic snails were generally less abundant where there was vehicle traffic. However, in the intertidal zone one snail showed the opposite pattern. There was less change in the community structure at sites where vehicles spread out across the foreshore than at sites where all vehicles travelled in a narrow lane, but this reduction in impact was offset by a greater area being affected. This study provides preliminary evidence of a measurable impact on sediment and community composition at 16 vehicle trips per day and suggests that management needs to consider the tradeoff between magnitude of impact and area affected.