DETERMINANTS OF BENTHIC BIOGEOGRAPHY IN THE OCEANS

Understanding the evolution of first-order marine biogeographic structure is critical for a large suite of theoretical and applied questions. Common practice defines modern marine bioregions based on a blend of biotic and abiotic attributes, which renders their detection in deep time difficult and the reasoned identification of abiotic controls circular. Based on network-analysis of occurrence data alone, we outline eleven spatially coherent, first-order bioregions of extant marine benthic animals. Taxonomic differences among bioregions are mostly governed by species replacement, but bioregions neighboring the Indo-Pacific are partially nested. Bioregions are consistent among distantly related taxa, suggesting common drivers. The general distribution of bioregions is forced by land and ocean barriers, while multivariate analyses show sea surface temperature to be the main predictor of contacting biogeographic boundaries. By tracing provinciality over geologic time, we identify plate tectonics as its dominant driver, whereas long-term climate change appears to have little effect on global-scale bioregionalization. As turnover is largely driven by temperature gradients, we argue that bioregion boundaries can be maintained as long as temperature variance within a region is smaller than between regions. We predict that the basic biogeographic structure of the oceans will be essentially maintained in the foreseeable future, although boundaries are likely to shift poleward. However, as severe environmental disturbances have the capacity to adversely affect bioregionalization, provinciality can be disrupted in the event of an anthropogenic mass extinction.