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Guest M.A.,University of Tasmania | Hirst A.J.,University of Tasmania | Hirst A.J.,Marine and Freshwater Fisheries Research Institute | Nichols P.D.,CSIRO | And 2 more authors.
Marine Ecology Progress Series | Year: 2010

Stable isotopes of carbon and nitrogen and fatty acid analyses are increasingly being used in combination to determine the trophic structure of marine systems. For stable isotopes, the variability in carbon and nitrogen isotopic signatures has long been recognised and has been characterised for some taxa. Whilst it is known that metabolic processes may influence fatty acid profiles, the spatial variability of fatty acid profiles has not been documented. Understanding at what scale these 2 biochemical tracers vary, and if the scale of variability corresponds between tracers, is crucial for the correct design and interpretation of combined tracers in trophic studies. This study is the first to examine spatial variability in fatty acid profiles per se, and in combination with stable isotope ratios in the same organisms at multiple spatial scales. We used a spatially hierarchical design which sampled across broad geographic regions, reefs within regions, and also between different parts of macroalgal plants common on temperate reefs. For stable isotopes of carbon and nitrogen, variability was greatest at intermediate spatial scales (between locations within regions, and sites within locations). In contrast, fatty acid profiles showed the greatest variation amongst individual replicates of lobster, abalone and macroalgae. This study demonstrates that for the increasing number of trophic studies using combined biochemical tracers, sampling design should cater to the differences in the variability of each tracer technique and allocate sampling accordingly. Copyright © Inter-Research 2010.

Johnson P.,CSIRO | Fulton E.,CSIRO | Smith D.C.,CSIRO | Jenkins G.P.,Marine and Freshwater Fisheries Research Institute | Barrett N.,Tasmanian Aquaculture and Fisheries Institute
Natural Resource Modeling | Year: 2011

Ecosystem processes function at many scales, and capturing these processes is a challenge for ecosystem models. Nevertheless, it is a necessary step for considering many management issues pertaining to shelf and coastal systems. In this paper, we explore one method of modeling large areas with a focus at a range of scales. We develop an ecosystem model that can be used for strategic management decision support by modeling the waters off southeastern Australia using a polygon telescoping approach, which incorporates fine-scale detail at the coastal zone, increasing in scale to a very coarse scale in the offshore areas. This telescoping technique is a useful tool for incorporating a wide range of habitats at different scales into a single model. © 2011 Wiley Periodicals, Inc.

Macreadie P.I.,University of Melbourne | Macreadie P.I.,University of Technology, Sydney | Hindell J.S.,Arthur Rylah Institute for Environmental Research | Keough M.J.,University of Melbourne | And 3 more authors.
Ecology | Year: 2010

According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation, Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0-0.5 m) and interiors (0.5-1 m) of two patch configurations: continuous (single, continuous 9-m2 patches) and patchy (four discrete 1-m2 patches within a 9-m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass edges due to greater food availability, and provide experimental support for the resource distribution model as an explanation for edge effects. © 2010 by the Ecological Society of America.

Jung C.A.,University of Melbourne | Swearer S.E.,University of Melbourne | Jenkins G.P.,Marine and Freshwater Fisheries Research Institute
Marine and Freshwater Research | Year: 2010

Comprehensive assessment of spatiotemporal variation in assemblages, particularly relating to management and conservation efforts, should include examination of variation across scales. The present study investigated spatiotemporal variation at various scales in the fish fauna of Port Phillip, Australia, over 17 years. There were significant increases in diversity and changes in faunal composition in the most recent study, compared with 17 (+38%) and 7 (+151%) years ago. No significant year-to-year differences and no fortnightly differences within a season were found, supporting the notion of long-term changes. However, inter-seasonal variation was significant, with diversity highest in summer and lowest in winter (42.3% of summer diversity), illustrating substantial variation only at particular scales. The spatial structuring of assemblages was consistent at all temporal scales over 17 years. Fish assemblages and diversity varied significantly among sites and regions, but diversity was always highest on reefs in the eastern region of Port Phillip. However, the majority of spatial variation occurred among replicate transects (up to 75% of overall variation). Despite the high degree of small-scale spatiotemporal variability, the results provide evidence of long-term changes in faunal composition and diversity within the bay. Moreover, the results underline the necessity for multi-scalar approaches in ecological studies like abundance assessments. © 2010 CSIRO.

Smith T.M.,Victorian Marine Science Consortium | Smith T.M.,University of Melbourne | Hindell J.S.,University of Melbourne | Hindell J.S.,Arthur Rylah Institute for Environmental Research | And 4 more authors.
Journal of Fish Biology | Year: 2011

Diets of the pipefish Stigmatopora nigra were analysed to determine if food availability was causing S. nigra to distribute according to habitat edge effects. Gut analysis found little difference in the diets of S. nigra at the edge and interior of seagrass patches, regardless of time of day or season. Fish diets did, however, vary with seagrass density: S. nigra in denser seagrass consumed more harpacticoid copepods and fewer planktonic copepods. The lack of difference in prey eaten by S. nigra at the edge and interior of patches suggests either that food was not determining S. nigra distribution patterns within patches or that differences in fish densities across patches meant that relative fish-prey densities were similar at edge and interior positions. Alternatively, any edge effects in diet might be masked by gradients in seagrass structure. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

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