| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | August 7, 2017 |
| Latest Amendment Date: | August 7, 2017 |
| Award Number: | 1737311 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Daniel J. Thornhill
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2017 |
| End Date: | July 31, 2020 (Estimated) |
| Total Intended Award Amount: | $427,526.00 |
| Total Awarded Amount to Date: | $427,526.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
266 Woods Hole Rd. Woods Hole MA US 02543-1535 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | BIOLOGICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Ocean warming kills corals and efforts are underway to identify and protect coral reefs that may withstand the projected 21st century rise in tropical ocean temperatures. Coral reefs in the central equatorial Pacific (CEP) have been exposed to episodes of extreme warmth every 3-7 years for centuries, if not millennia, yet remain highly productive ecosystems. Initial data obtained by the investigator from stress signatures archived in the skeletons of long lived coral species, suggests that CEP reefs lose their symbiotic algae or bleach, sometimes severely, during warm episodes. The observation that CEP reefs bleach repetitively yet remain productive implies uncommon resilience to ocean warming. The investigator will use laboratory experiments and field observations to validate skeletal records of historical bleaching. A successful outcome will provide novel and valuable insights into the resilience of the CEP reefs and a new tool with which to identify thermally tolerant coral reef ecosystems across the tropics. Additionally, this project includes mentorship of a postdoc and six undergraduate or high school students, outreach through presentations and media, and expansion of publically available software for coral stress band analysis.
Ocean warming projections indicate severe impacts to coral reefs will occur on an annual basis within the next few decades. Consequently, a coordinated effort is underway to identify reefs that might survive these changes. The investigator will test the hypothesis that such reefs exist at the epicenter of influence of the El Niño-Southern Oscillation (ENSO), where strong inter-annual temperature variability creates conditions conducive for the development of thermal resilience. The project uses laboratory-based bleaching experiments and actual stress signatures accreted by wild corals during the 2015 El Niño to validate signatures of historical bleaching archived in the skeletons of massive reef building corals. In addition the investigator will use new, long cores from the CEP to build a robust dataset of historical bleaching back to the 1800's. A successful outcome will increase confidence in the interpretation of skeletal stress bands as quantitative bleaching proxies and enable the reconstruction of the history of coral reef bleaching and recovery in the CEP.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Coral reefs globally are under threat from ocean warming and the increase in frequency and intensity of heatwaves. In the central equatorial Pacific, coral reefs have been exposed to El Nino-induced heatwaves hundreds if not thousands of years, yet maintain relatively high coral cover and diverse coral populations. Understanding the factors that enable these reefs to respond to, and recover from, frequent heat exposure will inform management strategies for reefs under global warming and improve model projections of reef futures that do not currently consider adaptation.
Historical bleaching data is key to understanding the reef response yet observational data in this remote region is sparse: only two direct observations of coral bleaching have been made, both during the 2015/16 El Nino. To fill these vast spatial and temporal gaps in observational data, we developed a bleaching proxy based on high-density skeletal stress bands accreted by massive corals. Under this award, we developed an automated code to identify and quantify bleaching stress bands in 3-D CT-scan images of coral skeletons. We established a robust link between bleaching and skeletal stress bands by showing that prolonged bleached causes starvation, a reduction in coral tissue biomass, and cessation of skeletal extension (upward growth) that leads to formation of anomalously high density "stress" bands.
Using skeletal cores and bleaching observations from 11 Pacific and Atlantic coral reefs, we established a robust link between the proportion of Porites (Pacific)/Orbicella, Siderastrea (Caribbean) that form stress bands during a heatwave, and the observed percent bleaching on the reef during that heatwave. This means we can use the stress band proxy to identify bleaching events that were not directly observed, and to estimate the severity of bleaching on different parts of the reef. Applying the stress band proxy in the central equatorial Pacific, we demonstrated a clear partitioning of thermal tolerance amongst different reefs linked to the history of thermal stress exposure of each island. Coral communities exposed to a history of frequent strong heatwaves had higher heat tolerance than those exposed to less frequent and severe heatwaves.
Using long skeletal cores extracted from old, massive coral colonies, we reconstructed a 100 year-long history of bleaching in the central equatorial Pacific, spanning 1920 to 2020. We uncovered 20 regional scale bleaching events during this time period, of which the 2015/16 event stands out as the most severe by far.
This award supported two post-doctoral fellows, one PhD thesis, one Master?s thesis, three undergraduate senior theses, and a high school science fair project. Results were disseminated through two documentary films posted on YouTube, multiple public speaking engagements including the UN General Assembly, the Polynesian Leaders Group Summit and the UN Ocean Decade. 3-D meter-scale hydrodynamic models of two coral reef islands were developed. Nine manuscripts have been published, submitted or prepared for publication in international peer reviewed journals. All published data and codes are publically available on BCO-DMO.
Last Modified: 02/13/2021
Modified by: Anne Cohen
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