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Implications of habitat type on the hyperbenthos of two morphologically divergent estuaries, and their adjacent nearshore marine waters, along the lower west coast of Australia

Coen, Natasha (2016) Implications of habitat type on the hyperbenthos of two morphologically divergent estuaries, and their adjacent nearshore marine waters, along the lower west coast of Australia. PhD thesis, Murdoch University.

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This study characterised the nearshore habitats and hyperbenthic fauna of two permanently-open but morphologically divergent estuaries along Australia’s lower west coast (the Swan-Canning and Peel-Harvey). The overarching aim was to assess whether spatial differences in the environmental characteristics of habitats could be used as a reliable basis for predicting those in faunal composition. The hyperbenthos of these temperate microtidal estuaries were also compared to that in the nearby coastal waters, and used to test several paradigms about faunal differences between estuarine and marine environments. This is the first hyperbenthic study in any Australian estuary.

A quantitative approach was developed for classifying local-scale estuarine habitats using environmental criteria that were ecologically-relevant, readily available and enduring. It was applied to the above estuaries then expanded to account for geographical region and estuarine bar state and applied to two other south-western Australian systems, the seasonally-open Wilson Inlet and normally-closed Wellstead Estuary.

Sampling of the hyperbenthos at various habitats throughout the Swan-Canning and Peel-Harvey estuaries in winter 2005 and summer 2006 yielded 72-92 species, 10-12 phyla (mainly Crustacea) and 5,602-9,347 individuals in each system. Mean species richness, density, diversity and composition differed significantly among habitats in each estuary and season, although not always between all habitats. Habitat differences in the hyperbenthos were almost always significantly correlated with those in the environmental attributes, indicating that the classification scheme provides a reliable basis for predicting these fauna at any unsampled site in these estuaries.

Comparisons of the hyperbenthos between the above estuaries and that in the adjacent coastal waters showed that both the mean number of species and density were far greater in the marine than estuarine environments, while mean diversity was similar in all systems except the Peel-Harvey in summer, where it was significantly lower. The trends in species richness support widely-accepted paradigms of faunal differences between estuarine and marine waters, those in diversity provide partial support, while those in density are in profound opposition. Species composition differed extensively between the estuarine and marine waters, and also differed between the two estuaries but to a far lesser extent.

As the first study of the hyperbenthos in Australian estuaries, and to compare these assemblages with those in adjacent marine environments, this thesis provides extremely valuable insight into these fauna and builds on the relatively limited knowledge of hyperbenthos in the southern hemisphere.

Publication Type: Thesis (PhD)
Supervisor: Valensini, Fiona and Potter, Ian
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