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Abstract

BIOTIC TURNOVER ON REEFS OF THE CARIBBEAN AND EASTERN PACIFIC: HOLOCENE SURPRISES AND FUTURE PROJECTIONS.

Richard B. Aronson¹, Ian G. Macintyre², and William F. Precht^3
1Dauphin Island Sea Lab
²National Museum of Natural History
³Battelle Memorial Institute
Bio

Although coral reefs are degrading globally at present, widespread mass mortalities of dominant, framework-building corals first occurred in the Caribbean and eastern Pacific in the 1980s. Real-time observational data can be combined with millennial-scale paleobiological records to explore the geological implications of ecological phase shifts in both regions. Populations of acroporid corals died off catastrophically from disease in the Caribbean during the 1980s–90s, and their loss depressed coral cover regionally. Coring studies in Belize and Jamaica revealed that the Acropora-kill, and the ensuing replacement of Acropora by coral taxa that are not framework builders, were unprecedented events in at least the last 3000–4000 years. Rates of vertical reef accretion have been slowed or halted over the last 25 years. In the eastern Pacific, populations of Pocillopora damicornis were bleached and killed by the 1982–83 El Niño event. Coral mortality and subsequent bioerosion of reef frameworks suggested that centennial-scale recurrences of strong El Niños are responsible for the slow accretion rates of eastern Pacific reefs. Off the Pacific coast of Panamá, Pocillopora recovered rapidly after 1983 in some places. Where it did not recover the Pocillopora rubble was colonized by Psammocora stellata, which is not a framework builder. Coring studies in progress in the Gulf of Panamá are showing that Pocillopora-kills and shifts to Psammocora had occurred previously during the past 3000–4000 years; however, Pocillopora growth was suppressed continuously for centuries, depressing vertical reef accretion for far longer than the return time of individual, strong El Niño events. These depressed rates of reef growth can be used to parameterize models of vertical accretion under long-term scenarios of biannual to annual coral bleaching, predicted to commence in the next several decades.