Biodiversity 'hotspots', patterns of richness and endemism, and taxonomic affinities of tropical Australian sponges (Porifera)

'Hotspots' of biodiversity (taxonomic richness, endemism, taxonomic affinities between communities) at small (alpha), medium (beta) and larger (gamma) scales of diversity were examined for marine sponge populations throughout tropical and subtropical Australia, with the faunas of Vanuatu, Palau and Thailand used as outgroups for comparison. Spatial and numerical (ordination) models and hierarchic classifications delineated 37 beta and 13 gamma scale faunas from 1343 investigated localities using a pool of 2324 species. The Australian taxonomic literature was ignored completely to avoid the many still unresolved taxonomic problems and to allow equal treatment of collecting localities. Richness and endemism varied considerably between marine areas, for species and genera at all spatial scales, with gradients strongly corroborated by hierarchic taxonomic relationships between faunas. Richness and endemism were equally effective indicators of biodiversity 'hotspots', whereas species-level vs. genus-level data produced differing patterns, with the latter substantially underestimating biodiversity and marine area relationships, and consequently a poor 'surrogate' for species data. Patterns of taxa shared between adjacent areas were more informative than richness and endemism data alone, as they more accurately reflect the processes in these areas. Latitudinal gradients in sponge diversity were not evident, whereas various environmental factors were prominent at alpha scales and biogeographic factors were prominent at beta and gamma scales of diversity. An example of a small (alpha) scale diversity fauna revealed substantial spatial heterogeneity (mean of 41 spp/locality, 33% apparently endemic, and a total fauna of 226 spp) containing few ubiquitous species (40% or 78 spp), with adjacent reefs having relatively low faunal similarity (mean 33%). Faunas at the medium (beta) scale of diversity were less heterogeneous (mean 127 spp/region, 27% apparently endemic to a particular region, with a total fauna of 2324 spp), containing a significantly larger dataset (829 spp) found in >1 region to assess taxonomic affinities. At the larger (gamma) scale of diversity faunas were far more heterogeneous (mean 263 spp/region, 47% apparently endemic to a particular region) containing a smaller dataset (only 588 spp or 26% of the fauna with >1 species/region) to assess taxonomic affinities. Consequently, sponge faunas at the alpha and gamma scales of diversity are ineffective and inappropriate as biodiversity models, respectively, with gamma scale diversity also less relevant as a practical tool for marine resource management and marine area conservation.