LATE MIOCENE TO RECENT CORAL COMMUNITY DYNAMICS IN THE GULF OF CALIFORNIA

Hermatypic coral studies in the Gulf of California have focused mainly on the distribution, abundance, ecology, and biogeography of modern species, but relatively few of these works have studied fossil corals. An interinstitutional and multidisciplinary research team is targeting Miocene to Pleistocene coral communities in the Gulf of California in order to assemble a detailed geologic and taxonomic framework for already known and new coral bearing units. In general, coral bearing units are small and represent single spatio-temporal growth episodes ranging in age between late Miocene to late Pleistocene. Identification of recently collected specimens reveals that previously recognized coral species probably represent ~ 50 % of the Gulf of California fauna. Cluster analysis, multidimensional scaling and analysis of similarity of presence/absence and relative abundance data demonstrated that Gulf of California coral reef assemblages experienced larger temporal differences in species composition and relative abundance than expected by chance. Coral species originated and were added to the species pool during late Miocene-early Pliocene and Pleistocene. Gulf of California assemblages consisted of locally originated Caribbean-like species between late Miocene and late Pliocene when extinction peaked at the Plio-Pleistocene transition. During the Pliocene assemblages consisted of a mix of extinct and living species co-occurring within and among localities, but immediately after the demise of pre-turnover taxa, living Indo-Pacific immigrant species dramatically increase in number and relative abundance ruling out ecological replacement as the key factor in pre-turnover species extinction. The turnover is unique in that pre-turnover species origination resulted from the formation of the Gulf of California, and instead of reducing species richness, the extinction event triggered the long-distance colonization of species. More data and better resolved age dates are necessary to understand the cause of faunal turnover, and the relative importance of biological and environmental factors in the faunal change.