Award: OCE-1619893

This project was developed in response to the El Niño of 2015-16 that threatened to kill coral reefs through high seawater temperatures. Previous strong El Niño events caused catastrophic coral death, notably in 1998 when large areas of coral reef bleached and died. Therefore, the possibility that the 2015-16 El Niño would be a "monster" event was cause for great concern. The best places to study El Niño effects on coral reefs are locations where they have been investigated for decades, and in this regard, Mo?orea, French Polynesia, is exceptional. Since 2004, NSF has supported coral reef research in this location through the Long Term Ecological Research (LTER) program, and by 2015, it provided a decadal context within which the effects of 2016 could be interpreted. With RAPID funding, this project focused on the effects of El Niño on the appearance of baby corals on the reef through a year-long program of field ecology. This program provided unique opportunities for graduate students to assist with important research, to develop research leading to their MS degrees, and to strengthen their capacity to contribute to the scientific and educational workforce as globally-aware and technically competent professionals. As this project began in early 2016, El Niño was proving to be very harmful for Australian coral reefs, as well as those in many other western Pacific locations. While large swaths of coral were dying throughout 2016 on many reefs, a different outcome unfolded in Mo?orea. First, despite warnings of severe warming, seawater temperature increases in Mo?orea were modest. Late summer temperatures reached 30.0°C, but were above the decadal average for only a month; in the fall, they were above the decadal average for several months, although they did not reach harmfully high values. The late summer temperatures caused minor coral bleaching, but recovery was complete within 3–4 months, and bleaching did not occur in the fall. Terracotta floor tiles attached to the reef in January 2016, provided settlement surfaces for baby corals, and when these were inspected in August 2016 and January 2017, they revealed more baby corals than had been seen over the previous decade, and they reflected different abundances of the types of coral usually found in Mo?orea. Therefore, while the El Niño of 2016 created unusual temperatures in Mo?orea, the effects on the corals were different from those in other parts of the Indo-Pacific. In Mo?orea, the recent history of these reefs seems to have created communities that are resistant to some kinds of environmental disturbances, and these effects "primed" the corals to respond in beneficial ways to the 2016 El Niño. There is more to understanding the effects of El Niño on coral reefs than just counting the number of baby corals, for their survival determines the kind of reef that ultimately will develop. This project addressed these effects in two ways, first by evaluating the roles of existing corals in determining the survival of baby corals (i.e., "density-dependent effects"), and second, in determining whether the arrival time of baby corals determines the kind of communities they develop (i.e., "priority effects"). Density-dependent effects were studied by recording the number of baby corals in plots with reduced coral abundance, and in these locations the number of baby corals increased 65%. These results indicate that the implications of increased densities of baby corals will be accentuated where less coral is initially present. Finally, to address priority effects, patio pavers were installed on the reef in four seasons, and currently they are being evaluated for the kinds of community that develops on summer-, fall-, winter-, and spring- deployed pavers. This aspect of the project is slow to generate results, as they can only develop as fast as the corals appear. Maintaining this experiment as part of the monitoring research in this location will provide insight into whether the El Niño of 2016 initiated events that will change the coral reefs through the appearance of large numbers of baby corals. The resilient reefs of Mo?orea provide some optimism for the global fate of coral reefs, and perhaps the lessons that can be learned in this location can be used to good effect to enhance the survival of coral reefs for future generations. This important message has been conveyed to the scientific community through publications and conference presentations, and has been integrated into high school classrooms through presentations, lesson plans, and independent study projects. Last Modified: 01/01/2018 Submitted by: Peter J Edmunds