Abstract
Ocean warming is negatively impacting coral reef ecosystems and considerable effort is currently invested in projecting coral reef futures under 21st century climate change. A limiting factor in these projections is lack of quantitative data on the thermal thresholds of different reef communities, due in large part to spatial and temporal gaps in bleaching observations. Here we apply a coral bleaching proxy, skeletal stress bands, to reconstruct the history of bleaching on eight coral reefs in the central equatorial Pacific (CEP) and use this information to constrain the thermal thresholds of their coral communities. First, three genera of massive corals collected on both Pacific and Caribbean reefs are used to derive a calibration between the proportion of corals that form stress bands during a bleaching event, and the total observed bleaching incidence in the community of mixed coral taxa. The correlation is highly significant, indicating that stress bands in massive corals reflect community-level bleaching severity (R2 = 0.945, p < 0.001). We applied the calibration to stress band records from eight Pacific reefs, reconstructing their bleaching histories over the period 1982 to 2015. A percentile-based method of estimating thermal stress (Degree Heating Weeks) for CEP reefs was developed and applied. Comparing the level of thermal stress experienced by each coral community during each event with the reconstructed bleaching response, we characterized the thermal sensitivities of each reef community and quantified the thermal threshold (b½) at which 50% of the coral community bleached. Our analysis reveals a unique non-linear thermal response curve for each reef. The most thermally tolerant reefs in the study (Jarvis and Kanton Islands) experienced 50% bleaching at seven to nine times more thermal stress than did the least resistant reef in the study (Maiana Island). An exploration of the potential drivers of thermal tolerance revealed a strong correlation between b½ and the history of thermal stress events in each reef system. Thermal tolerance was also correlated with concentrations of dissolved inorganic nitrate in the water column and with estimates of coral energetic reserve.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 743-757 |
| Number of pages | 15 |
| Journal | Coral Reefs |
| Volume | 38 |
| Issue number | 4 |
| DOIs | |
| State | Published - May 2 2019 |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledgements: We gratefully acknowledge the Government of Kiribati and the Phoenix Islands Marine Protected Area (PIPA) Trust for access to the PIPA and for permission to core corals on Maiana and in the PIPA. The US Fish and Wildlife granted permission to collect coral samples on Jarvis and Howland Islands. Fieldwork on Dongsha Atoll was conducted with the support and permission of the Dongsha Atoll Research Station. We thank the Palau International Coral Reef Center and the Palau Bureau of Marine Resources for logistical support and permission to sample corals on Palau. We thank the Coastal Zone Management Unit, Government of Barbados, the Ministry of the Environment on Martinique, and the Carmabi Foundation, Curacao for assistance with permitting and coral sampling on the Caribbean Islands. Fieldwork on Jarvis, Howland, Maiana, Martinique, Barbados and Curacao was made possible by Pangaea Exploration and their vessel Seadragon, Captain Eric Loss and his crew. We are extremely grateful for their expertise, enthusiasm and continued support of our mission. Funding was provided by the National Science Foundation (NSF OCE 1737311 and 1601365 to ALC, a WHOI Access to the Sea Award to ALC, and the Atlantic Donor Advised Fund to ALC. The National Science Foundation Graduate Research Fellowship supported AA, TD, and HB, the National Defense Science and Engineering Graduate Fellowship supported HR, the Woods Hole Oceanographic Institution Summer Student Fellowship and the Cornell Hunter R. Rawlings III Presidential Research Scholars Program supported CSB. The Prince Albert 2 of Monaco Foundation, the Akiko Shiraki Dynner Fund, the New England Aquarium, the Martin Family Society Fellowship for Sustainability, the Gates Millenium Scholarship, American Association for University Women American Dissertation Fellowship, the NOAA Coral Reef Conservation Program, and the Ocean Ventures Fund at Woods Hole Oceanographic Institution also provided support. Additional operational support was provided by the scientific staff of the NOAA’s Pacific Islands Fisheries Science Center and the officers and crew of the NOAA ship Hi'ialakai. The views expressed are the authors’ own and not necessarily those of the U.S. Government.
