The response of estuarine fauna to salinity perturbations : towards a tool box for monitoring ecological change
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Estuaries are important transitional zones between terrestrial, marine and freshwater habitats. Estuarine ecosystems are increasingly under pressure from global population growth concentrated on the coasts. Effective management to sustain estuarine ecosystem health requires knowledge and understanding of how productivity and biodiversity are affected by coastal development, as well as development of effective, affordable and practical tools for monitoring when and where human activities produce ecological impacts. Macroinvertebrates commonly display distributional gradients in abundance and richness that correlate to natural and anthropogenic disturbances and therefore can be an excellent option for ecosystem health checks. Identification and enumeration of invertebrates is time consuming and expensive particularly for Australian estuarine invertebrates, for which taxonomic expertise is not widely available and for which natural distributions and sensitivities to pollution gradients are poorly documented. Strategies for optimizing ecological monitoring based on invertebrates, for example use of surrogate species or coarse taxonomic resolution, are urgently required to make estuarine ecosystem assessments more accessible. My project focused on responses of estuarine invertebrate communities to changes in salinity; an important environmental variable that is altered by climate change, over extraction of catchment water, damming and waste-water discharge. I initially made use of an eight year data set from the Hawkesbury River estuary, New South Wales, Australia, linking macroinvertebrate community structure to salinity, to test hypotheses about whether spatio-temporal variation in surrogate species or communities (resolved to coarse taxonomic resolution) correlate with spatio-temporal variation in whole communities of invertebrates identified to species. Then, using a mesocosm experiment, I tested for causality between salinity and the structure of sediment-dwelling invertebrate communities exposing them to medium-duration perturbations. My analyses confirmed salinity significantly correlated with benthic invertebrate assemblage structure, with a minor effect attributable to sediment mean grain size and percentage of mud (< 63 µm). I identified 14 taxa that correlated well with spatio-temporal patterns in the full biotic community. I found resolution of taxa to Family level was generally sufficient to capture the main sources of variation in response to salinity such that monitoring can therefore confidently utilise surrogates or a coarser taxonomic resolution allowing funding priority for sampling effort instead of sample processing. My mesocosm study suggests that salinity perturbations result in shifts in macro-invertebrate assemblages. Based on these results, I provide recommendations for effective and efficient monitoring of estuarine ecosystems using macroinvertebrate communities.
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