Scientists have made a surprising discovery regarding the impact of El Niño events on coral reefs. They found that specific ocean processes associated with El Niño can help coral reefs withstand the heat stress caused by climate change. One such process is the intensified North Equatorial Counter Current, which brings cooler and nutrient-rich waters to certain reefs, offering protection against heat-induced bleaching. These findings have important implications for future coral reef conservation strategies.
Climate change has led to the emergence of marine heatwaves, which pose a significant threat to coral reefs, as they rely on corals that form their foundation. Researchers have now identified a phenomenon that could assist coral reef managers in planning and responding to future challenges.
El Niño, a cyclic climate pattern occurring in the tropical Pacific every few years, causes notable changes in winds, weather, and ocean temperatures. From April 2015 to May 2016, one of the strongest El Niño events ever recorded occurred in the Central Pacific.
During this event, coral reefs in the region experienced extreme stress due to warmer ocean temperatures, resulting in mass bleaching and the expulsion of symbiotic algae, causing the corals to turn white. However, scientists from KAUST, in collaboration with international colleagues, discovered localized ocean processes during this El Niño event that provided crucial nourishment to the coral reefs of Palmyra, a Central Pacific island. As a result, these reefs not only survived but thrived, revealing valuable insights into how different coral reefs respond to stress.
The remote and highly protected status of Palmyra Atoll in the Pacific Ocean makes it an ideal living laboratory for studying the impact of climate change on coral reefs. Researchers aim to use this knowledge to identify naturally protected reefs, which could serve as potential sources for repopulating corals that face greater exposure to climate change impacts.
“We were unaware that something positive could arise from El Niño,” says Michael Fox, a coral reef ecologist from KAUST. He further explains that the same processes responsible for coral reef mortality on equatorial islands actually created favorable conditions slightly further north. The unexpected benefit of these processes during a significant El Niño event is a remarkable finding.
One significant discovery made by Fox and his team relates to the 2015-16 El Niño event. While the equatorial islands of Kiritimati and Jarvis, located just 700km south of Palmyra, experienced coral reef die-offs due to increased ocean temperatures, Palmyra’s reefs survived. The key factor was the strengthening of the eastward-flowing North Equatorial Counter Current, which delivered cooler waters rich in plankton to Palmyra’s reefs. Combined with a shallower sea surface layer around the island, this process allowed the reefs to better tolerate the heat stress caused by rising ocean surface temperatures.
Ocean models utilized by Fox and his colleagues revealed that the life-saving processes observed during the 2015-16 El Niño were also present during the other two major El Niño events of the past half-century. These ocean processes played a crucial role in helping Palmyra’s corals survive extreme marine heatwaves in the past, and they may continue to do so in the future.
“El Niño-associated heatwaves pose the greatest threat to coral reef ecosystems worldwide,” Fox emphasizes. “These events have far-reaching consequences in the tropics and can lead to mass coral mortality over vast areas. Identifying coral reefs with a higher chance of survival during such extreme events is crucial for understanding the future of coral reef ecosystems.”
The study’s findings raise an important question: Are there other locations where similar ocean conditions align during El Niño events, resulting in better-than-expected reef conditions?
“Our study provides a roadmap for identifying reefs that are defying the global decline trend,” says Fox. “This information will be vital for Pacific islands’ residents as they determine the placement of marine protected areas and plan for the future.”
Palmyra Atoll was an ideal research site due to its isolated and uninhabited status as a U.S. federally protected island. Since 2006, it has housed a small research station established by The Nature Conservancy. By comparing the responses of coral reefs in Palmyra to those in more degraded or disturbed areas impacted by human activities, researchers were able to establish connections between ocean processes and coral survival that would otherwise be challenging to isolate.
“Palmyra Atoll serves as a perfect living laboratory for studying the impact of climate change on coral reefs and identifying factors contributing to reef resilience,” explains Joseph Pollock, a senior coral reef resilience scientist at The Nature Conservancy’s Hawaii & Palmyra Programs. He highlights that Palmyra’s reefs have maintained their ecological integrity due to their remote and highly protected status, unlike many reefs worldwide that have declined due to local stressors such as pollution and overfishing. This comparison enables researchers to better comprehend the specific effects of climate change.
Fox’s Ecological Oceanography Lab at KAUST plans to continue studying Palmyra and expand their research to the Red Sea. Their collaborative work involves KAUST, Bangor University (U.K.), Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration (U.S.), and The Nature Conservancy.
“Our research group combines organismal physiology, community ecology, and oceanography to identify patterns and processes that will support reef survival in the face of climate change,” explains Fox. “We are exploring similar questions in the Red Sea and striving to identify the physical processes that enable these unique reefs to persist in such an extreme environment.”
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Frequently Asked Questions (FAQs) about Pacific island reefs
What is the impact of El Niño events on coral reefs?
El Niño events have a surprising impact on coral reefs. Unique ocean processes associated with El Niño, such as the strengthened North Equatorial Counter Current, can bring cooler and nutrient-rich waters to some reefs, helping them resist heat-induced bleaching and survive the heat stress caused by climate change.
How do marine heatwaves affect coral reefs?
Marine heatwaves pose a significant threat to coral reefs. The increased ocean temperatures during these heatwaves lead to stress in corals, causing mass bleaching and coral mortality. Understanding how coral reefs can withstand or survive these heatwaves is crucial for their conservation.
What was discovered about Palmyra Atoll’s reefs during the El Niño event?
During the 2015-16 El Niño event, while nearby equatorial islands experienced coral die-offs, the reefs at Palmyra Atoll thrived. This was due to the intensified North Equatorial Counter Current, which delivered cooler and nutrient-rich waters to the reefs, helping them better manage the heat stress caused by rising ocean temperatures.
How can the findings of this study inform coral reef conservation strategies?
The study’s findings highlight the importance of identifying naturally protected reefs during El Niño events. These reefs could serve as potential sources for repopulating corals and could help inform the placement of marine protected areas and conservation planning in the face of climate change.
Why was Palmyra Atoll chosen as a research site?
Palmyra Atoll’s remote and highly protected status made it an ideal research site to study the impacts of climate change on coral reefs. Being uninhabited and federally protected since 2006, it provided a pristine ecosystem for studying the connections between ocean processes and coral survival, without the interference of human impacts.
What are the future research plans of the Ecological Oceanography Lab at KAUST?
The Ecological Oceanography Lab plans to continue studying Palmyra Atoll and expand their research to the Red Sea. They aim to identify the physical processes that enable unique reefs to persist in extreme environments and contribute to the understanding of reef survival in the face of climate change.
More about Pacific island reefs
- Science Advances: “Ocean currents magnify upwelling and deliver nutritional subsidies to reef-building corals during El Niño heatwaves”
- KAUST (King Abdullah University of Science and Technology): Ecological Oceanography Lab
- The Nature Conservancy: Palmyra Atoll
- Bangor University: School of Ocean Sciences
- Scripps Institution of Oceanography
- National Oceanic and Atmospheric Administration (NOAA)
- Red Sea Research Center, KAUST
