RAPID - The implications of El Nino-related bleaching on coral recruitment in Moorea

This research explores the effects of the 2015-16 El-Niño on coral reefs in French Polynesia where the US National Science Foundation supports a Long-Term Ecological Research site. El Niño brings a diversity of unusual conditions to the Pacific Ocean, but for coral reefs the most important effect is caused by seawater warming during the summer. Bleaching, the process causing corals to lose color and die, is a dramatic example of the negative effects of El Niño on reef corals, but high temperature also has insidious effects through impaired reproduction and poor recruitment of baby corals. As a result, El Niño conditions are likely to be associated with a degraded ability of coral reefs to regrow following disturbances, potentially preventing a full recovery, or favoring substantial changes in the community that develops. This research builds on the unrivalled history of LTER investigations in Moorea to ask how coral recruitment is affected by El Niño, as measured by the number of baby corals arriving to the reef, the number of baby corals that grow, and the kinds of communities that develop as a result of these events. The study involves fieldwork conducted in Moorea by faculty and graduate students, during which settlement tiles will be installed and monitored for baby corals, baby corals will be evaluated for overall ""health"", and natural and artificial reef surfaces will be quantified for community development. The results of this study will help to understand how marine ecosystems are responding to the spectrum of natural and human-related disturbances to which they exposed, including global climate change, and will improve the capacity to understand in what form coral reefs in US waters and throughout the world will survive the coming century. The project creates unique opportunities for graduate students to work in an international context, where they will conduct research promoting STEM careers, an appreciation of diverse tropical ecosystems, and the role of climate change in modifying ecosystem dynamics. The broader implications of this project will be strengthened by integrating the results into life science curricula at local high schools, in part by utilizing settlement tiles from Moorea in classroom exercises staffed by California State University Northridge graduate students.

This project addresses the effects of the 2015-16 El-Niño on coral recruitment in Moorea, French Polynesia, where coral reefs have been studied since 2005 thought the Moorea Coral Reef LTER. Time-series research supported by this program provides a unique historical context against which the ecological effects of the upcoming El-Niño can be gauged. As coral bleaching negatively affects coral reproduction, and previous El Niño events have been associated with globally-depressed coral recruitment, it is reasonably to hypothesize that coral recruitment in Moorea will change in magnitude (i.e., declining density) and type (i.e., taxonomic composition) over the next year. These possibilities have important implications, because coral recruitment mediates community resilience to disturbances, and modulates the trajectories of future reef development. In this 12-month project, a program of mensurative and manipulative experiments will be conducted to addressed four hypotheses: (1) coral recruitment will be depressed following El Niño-related seawater warming, (2) warming will affect post-settlement success of corals, (3) for Pocillopora, the effects on coral recruitment will be modulated through density-dependent processes, and (4) the resulting recruitment perturbations will modify trajectories of coral community development. The results of this research will have general application in revealing the demographic processes determining the response of coral reef communities to recurrent pulse disturbances such as El Niño events.