Environmental diversity as a reliable surrogacy strategy of marine biodiversity: A case study of marine mammals

Surrogates are used in conservation planning to select sites to represent species when information about species’ geographical distributions is insufficient. Many surrogates for biodiversity have used biotic (e.g., vegetation assemblages) or biogeographic distributions of a group of species (e.g., birds) that are easier to inventory than more cryptic species of interest. Because knowledge of species geographical distributions is mostly limited, environmental diversity (ED), an approach that uses environmental dissimilarity between sites to select areas for conservation, is a promising alternative surrogacy strategy. While studies in the terrestrial realms justify further investigations of the effectiveness of ED as a surrogate to determine conservation priority of sites, ours represents a significant expansion of this focus to consider the marine realm. In this study, we defined environmental space using nine variables and evaluated ED as a surrogate of global marine mammal species. We found that ED is an effective surrogacy strategy for marine mammals: sites selected to span environmental diversity represented 61% more marine mammals, on average, than a random subset of sites. Although the effectiveness of ED has been demonstrated in previous studies of terrestrial vertebrates, we believe this is the first time ED is assessed as a surrogate in marine systems at the global scale. Our findings suggest that ED may also be useful to prioritize sites for conservation of other marine taxa.