Australia's deep-water reserve network: implications of false homogeneity for classifying abiotic surrogates of biodiversity

Australia's southeast network of deep-water marine reserves, declared in July 2007, was designed using a hierarchy that represented the distribution of marine biodiversity as a nested set of bioregions. In this hierarchy, geomorphic units, individual or aggregations of seabed geomorphic features, are the finest scale used in the design process. We evaluated the interaction between two hierarchical levels (depth and geomorphic features), using video survey data on seamounts and submarine canyons. False within-class homogeneity indicated that depth, size, complexity, configuration, and anthropogenic impact need to be added as modifiers to allow geomorphic features to act as surrogates for biodiversity distribution. A consequence of using unmodified geomorphic surrogates, and of not correctly nesting geomorphic features within depth, is the diminished recognition of the importance and comparative rarity of megafaunal biodiversity of the continental margin (< 1500-m depths). We call this area the zone of importance, because it is where targeted marine impacts coincide with the greatest megafaunal biodiversity. Re. ning the geomorphic classification is desirable for future biodiversity characterization, but an alternative approach is to de. ne patterns in biodiversity and abiotic variables jointly, and to utilize finer scale information and provide a classification that preserves the maximum information of both datasets.