Deep sea biodiversity: Pattern and scale

• Michael A. Rex
• Donald R. Strong

Abstract
The primary aim of the workshop would be to relate patterns of biodiversity in the deep-sea benthos to the scales at which various processes act to shape these patterns. Deep-sea benthic communities have now been sampled on local, regional and global scales, but by many independent programs that have different objectives, use different methods and infer biogeographic patterns with different taxa or functional groups. Inevitably, this led to a welter of explanations of diversity that seem quite contradictory. At local scales, research has focused on how species coexistence can be mediated in an apparently homogeneous sediment environment. Precision sampling and manipulative experiments have provided convincing evidence that small-scale patchiness permits a large number of similar invertebrates to coexist by specializing on different types of patches or different successional stages of a patch. This suggests that the mosaic nature of the deep sea and the stochastic processes tied to patch formation permit high local diversity. At larger scales, however, definite geographic patterns of diversity emerge that cannot be accounted for by simple stochastic patch dynamics. Bathymetric patterns of diversity have been attributed to environmental gradients of nutrient input and the relative intensity of biological interactions, to geographic variation in sediment particle size heterogeneity and to large-scale disturbance. At global scales there are latitudinal gradients of diversity and strong interregional differences that appear to be correlated with the pattern and rate of surface production. At these very large scales the evolutionary processes that ultimately generate regional species pools and the historical spread of the deep-sea fauna must come into play as well. Species diversity in the deep sea, as in other environments, undoubtedly reflects an integration of ecological and evolutionary processes operating at different spatial and temporal scales. But because of the pace of discovery and independence of various research efforts, pattern and scale have not been synthesized for deep-sea communities. A critical discussion of this problem by experts working at different scales would contribute very significantly to reconciling theories of diversity and setting an agenda for future comparative and experimental research to test hypotheses on deep-sea biodiversity.