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Abstract:

The use of environmental data in biogeographic studies of the deep sea is providing
greater insight into the processes underlying large-scale patterns of
diversity. Recent surveys of Australia’s western continental margin (~100–
1100 m) provide systematic sampling of invertebrate megafauna along a gradient
of 22° of latitude (13–35° S). Diversity patterns of decapod crustaceans
were examined and we investigated the relative importance of environmental
and spatial predictor variables on both species richness (alpha diversity) and
species turnover. Distance-based linear models (DistLM) indicated a suite of
variables were important in predicting species turnover, of which temperature
and oxygen were the most influential. These reflected the oceanographic features
that dominate distinct depth bathomes along the slope. The numbers of
species within samples were highly variable; a small but significant increase in
diversity towards the tropics was evident. Replicated sampling along the margin
at ~100 m and ~400 m provided an opportunity to compare latitudinal patterns
of diversity at different depths. On the shallow upper slope (~400 m)
temperature was disassociated from latitude and the latter proved to be the
best predictor of sample species richness. The predictive power of latitude over
other variables indicates that proximity to the highly diverse Indo-West Pacific
(IWP) may be important, especially considering that almost 40% of species in
this study had a wide IWP distribution. In the management of Australia’s marine
environments, geomorphic surrogates have been emphasised when defining
areas for protection. We found sea-floor characteristics were relatively less
important in predicting richness or community composition.

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