Project: Identifying coral reef 'bright spots' from the global 2015-2017 thermal-stress event

NSF Award Abstract:
Coral reefs are one of the world's most diverse ecosystems that provide goods and services, such as fisheries and storm protection, for inhabitants of tropical and subtropical regions. However, the current rapid rate of climate change threatens the existence of coral reefs as they degrade because of thermal-stress events. Consequently, the coverage and coral composition of many coral reefs is changing. Most global models suggest that few if any reef corals will survive beyond the 2.5 degree Celsius temperature rise predicted for the tropical oceans within the next hundred years. Such predictions differ from recent field studies on coral reefs that show pockets where corals do not bleach and die. The disagreement between the global models and field assessments is a consequence of ignoring climate-change refuges; it is critical to locate the climate-change refuges and determine what circumstances are conducive for coral survival. The investigators will examine the global response of coral reefs to thermal stresses over the last two decades, and focus on the 2015-2017 El Nino event, which caused considerable thermal stress and coral bleaching. The investigators ask the question: Where are the coral reef 'bright spots' from the thermal-stress events? 'Bright spots' are considered as places with less than expected bleaching. The team will also assess why some localities are potential 'bright spots'. Identifying coral reef bright spots will help guide future conservation decisions by enabling managers to target reefs with specific characteristics, which could be protected from human encroachment and be designated as potential refuges from coral bleaching as climate change progresses. This project includes training of a post-doctoral fellow and a Ph.D student, and host a coral-bleaching workshop. This study will be of relevance to all persons that live and work near coral reefs. What happens to reef corals has cascading consequences on other reef-associated organisms, and also influences whether reefs can keep up with sea-level rise.

The current rapid rate of climate change threatens the existence of coral reefs as they degrade by thermal-stress events. A glimmer of optimism lies in the observation that thermal stresses vary spatially and temporally across the oceans, with the consequence that coral communities in different geographic regions, and under different local conditions, are likely to inherently differ in their capacity to tolerate thermal stress. One of the most transformative aspects of this work is in analyzing the extent to which the bleaching patterns differed from model predictions. This work will capitalize on the recent progress on Bright-Spots Analysis to assess unexpected outcomes. The investigators will take two approaches. First, the project will use a machine-learning algorithm, boosted regression trees to examine the relationships between coral bleaching and the environmental predictor variables of interest. Second, a series of generalized mixed effects models, within a hierarchical Bayesian framework, will be used to identify where geographically 'bright spots' from thermal stress are located and why some coral reefs are more susceptible to thermal stresses than others.