Recent important publication regarding the impacts of massive coral bleaching and mass mortalities in Caribbean coral reefs
Mass bleaching events have become a major cause of coral decline at a global scale as a result of increasing sea surface warming trends. In the summer/fall of 2005, the northeastern Caribbean region experienced a record-breaking sea surface warming event that resulted in a prolonged mass bleaching event, followed by a major disease outbreak, and significant coral cover decline of the principal Caribbean reef-building star coral Montastraea annularis. A recent study conducted by scientists of the University of Puerto Rico-RÃo Piedras Campus, published on January 20 in the open access journal Ecosphere (http://www.esajournals.org/toc/ecsp/2/1), revealed that populations of M. annularis have largely declined during the last decade and that its demography is highly susceptible to recurrent mass bleaching and mortality events as a consequence of climate change. The study was highlighted as the cover page of Vol. 2(1) of Ecosphere and showed that the viability of star coral populations is seriously comprised under the predicted global warming scenarios.
The study entitled â€œDemographics of bleaching in a major Caribbean reef-building coral: Montastraea annularisâ€ was published by Doctoral candidate, Raisa HernÃ¡ndez-Pacheco, and researchers Edwin A. HernÃ¡ndez-Delgado and Alberto M. Sabat, from the Center of Applied Tropical Ecology and Conservation, and the Department of Biology of the University of Puerto Ricoâ€™s RÃo Piedras Campus. It was part of the Coral Reef Long-Term Ecological Monitoring Program lead by Dr. HernÃ¡ndez-Delgado, in collaboration with Dr. Sabat, and funded by the National Science Foundation-CREST Program and the Caribbean Coral Reef Institute.
The study conducted during the last decade in Culebra Island, Puerto Rico, found out that the M. annularis population growth rate was in demographic equilibrium before the mass bleaching event, suffered a significant decline in growth rate for two consecutive years after the event in 2005, and demographically recovered three years after the event. However, prolonged bleaching caused dramatic colony fragmentation that resulted in a population made up almost entirely of small colonies by 2007 (97% were <50 cm2). A stochastic simulation model indicated that an annual probability of bleaching in excess of 6% would result in a decreasing population with a reduction of more than 54% in colony abundance after 100 years of projection. â€œIf the recurrence frequency of mass bleaching and mortality events, as strong as the one experienced in 2005, is higher than one every 17 years will lead star coral populations to nearly extinction during the next century or soâ€, said Raisa HernÃ¡ndez-Pacheco, lead author, and NSF-sponsored Ph.D. candidate at the University of Puerto Rico.
The article revealed that most of the effect that mass bleaching has on the population growth rate comes from changes in the survivorship of small colonies. Their findings further indicate that survival of small colonies will determine the viability of the M. annularis populations within the context of rising sea surface temperatures.
â€œThe problem is that M. annularis populations have declined by as much as 80% at some locations through the shallower reefs zones across the northeastern Caribbean. Most of the remnant populations were physiologically reduced to very small, highly isolated fragments, larval sexual recruitment on this species is extremely limited, and massive bleaching trends across the wider Caribbean have scaled up during the last three decades to at least once per decade. This recurrence is by far much more higher than what our model predicted, thus suggesting that under current trends M. annularis populations can disappear within the next 50 years or soâ€, said Dr. HernÃ¡ndez-Delgado, lead P.I. of CATECâ€™s CoralÂ Reef Research Group at the University of Puerto Rico.
Currently, these researchers are conducting further studies evaluating the long-term impacts of climate change-related factors and other local human factors on coral reef ecosystems across multiple biological organizational scales, from colony to ecosystem level. Further, sclerochronological studies are currently underway to elucidate long-term impacts of recurrent massive bleaching events on coral skeletogenesis.