Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution.

Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions.

A latitudinal gradient in northeast Pacific intertidal community structure: evidence for an oceanographically based synthesis of marine community theory.

Intertidal systems have been models for the study of the roles of competition, predation, and disturbance in determining community structure. These systems exhibit considerable regional variability in percentage cover and in the strength of interspecific interactions, which may be due largely to effects of varying larval supply. In Oregon and Washington, experimental studies of space allocation among sessile invertebrates have emphasized the role of benthic processes such as competition and predation. In contrast, studies in central California have emphasized the importance of larval supply. In this article, we identify a gradient in percentage cover in the middle and upper intertidal zone that is consistent with an oceanographically based explanation for these differences: percentage cover of mussels and barnacles is much higher in Oregon, where nearshore circulation promotes high recruitment, than in California, where strong offshore currents inhibit recruitment. A mathematical model incorporating larval transport and interspecific competition for space offers an explanation for the one violation of the hypothesis-higher percentage cover of Chthamalus spp. in California. The findings illustrate that attempts to synthesize regional differences in community structure and dynamics can benefit from considering both the benthic adult and pelagic larval environments.

Climate change, human impacts, and the resilience of coral reefs.

The diversity, frequency, and scale of human impacts on coral reefs are increasing to the extent that reefs are threatened globally. Projected increases in carbon dioxide and temperature over the next 50 years exceed the conditions under which coral reefs have flourished over the past half-million years. However, reefs will change rather than disappear entirely, with some species already showing far greater tolerance to climate change and coral bleaching than others. International integration of management strategies that support reef resilience need to be vigorously implemented, and complemented by strong policy decisions to reduce the rate of global warming.