Does Bioregionalisation Really Reflect Differences in Biodiversity? A Test of the Marine Bioregional Boundaries of Australia Using Gastropod Assemblages

The management of Australian coastal marine biodiversity is geographically delineated by bioregions defined under the Interim Marine and Coastal Regionalisation of Australia system (IMCRA). The location of boundaries between adjacent IMCRA defined bioregions is based on biotic and abiotic surrogates. Intertidal habitats are not well represented in the IMCRA model, so it is not known whether conservation plans based on IMCRA identified bioregions will effectively represent distinct communities for conservation. Here, I used gastropod molluscs as a model fauna because they are a significant component of intertidal assemblages. The model tested was that patterns of biodiversity exhibited by gastropods should align with IMCRA boundaries. Gastropods have been shown to be a reliable surrogate to assess patterns of biodiversity at larger scales. Tests were performed at different spatial scales under three different and complementary approaches, as surrogates can be effective under varying circumstances. At a continental scale, gastropods exhibited patterns of distribution coinciding with previous classic biogeographical models rather than IMCRA defined bioregions. At a scale of 103 km, gastropod assemblages did not coincide with boundaries set by IMCRA. The genetic structure of the microgastropod Eatoniella atropurpurea, a hyper-abundant species, again did not match bioregional boundaries. Thus, the general model that different bioregions support different assemblages was not supported in my study as the variability found at different spatial scales did not correlate with IMCRA defined boundaries The implications of these results are that different methods of conservation management at b large and fine scale are necessary for the design of marine reserves, as the current model (IMCRA) does not represent patterns of biodiversity at finer scale. New conservation tools must incorporate the natural variability in assemblage structure that occurs at finer scales