Coral reefs are in hot water: Could upwelling save the day?

Reference: Randall, C. J., L. T. Toth, J. J. Leichter, J. L. Maté, and R. B. Aronson. 2020. Upwelling buffers climate change impacts on coral reefs of the eastern tropical Pacific. Ecology101(2):e02918. DOI: 10.1002/ ecy.2918

Besides being great places to experience colorful marine life, coral reefs also provide us with other benefits like food and protection from large waves. Unfortunately, coral reefs across the globe have recently experienced more and more bleaching events. Corals are composed of living tissues that serve as a home to algae. They bleach, or turn white, when the tissues of the coral expel the algae living there. These bleaching events occur when the water gets too hot, which is happening more frequently because of climate change. Coral reefs typically do best in areas with warmer, stable water temperatures. Historically, coral reefs in coastal areas did not tolerate upwelling, which is when cooler water from the deeper parts of the ocean rises to the surface. But, with climate change increasing water temperatures globally, could upwelling and the cooler water it brings actually help coral reefs survive?

That’s the question that several researchers led by Carly Randall at the Florida Institute of Technology teamed up to answer. The researchers gathered historical data on coral cover and water conditions in two gulfs in Panamá: the Gulf of Panamá and the Gulf of Chiriquí. The Gulf of Panamá experiences strong upwelling for several months each year while the Gulf of Chiriquí does not. For the study, the researchers observed coral cover and water conditions during a natural cycle of climate patterns that occurred between 2015 and 2016, where ocean temperatures are warmer and nutrient poor, also referred to as El Niño. Because El Niño led to warmer water in the region for an extended period of time, conditions were ideal to explore what may happen in the future with the warmer water expected with climate change. By comparing historical data and current observations under conditions that resemble what the future may be in these two gulfs, the researchers were able to determine the role upwelling could play in coral survival.

This image shows a live, healthy coral reef in Panamá. Source: creativecommons.org

 

This image shows coral in Roatan Island, Honduras after a bleaching event. All of the algae that gives the coral its color has been expelled, leaving behind just the coral skeleton. Source: creativecommons.org
Changing Water Conditions

When the scientists looked at the historical data, they found that the Gulf of Chiriquí had warmer and more stable temperatures, which led to rapid coral growth. On the other hand, the Gulf of Panamá, where upwelling occurs, had less stable water temperatures and was cooler overall, leading to slower coral growth. Over the last 150 years, the water in both gulfs has warmed. But, in addition to becoming warmer, the temperatures in the Gulf of Chiriquí also became more variable. In contrast, during the El Niño event, the average temperature of the Gulf of Panamá did not increase even though the entire region had warmer water as a whole, whereas the Gulf of Chiriquí increased in temperature by about 1 degree Celsius.

This diagram shows how upwelling occurs. Source: Wikipedia

The corals responded to the changing water temperatures in both gulfs. The greater variability in water temperature in the Gulf of Chiriquí may have contributed to the loss of a little over 9% of the coral. During the El Niño event, the coral in the Gulf of Chiriquí experienced a bleaching event. Meanwhile, the coral in the Gulf of Panamá only experienced a loss of about 7% and did not experience any bleaching events during the El Niño, and actually had a higher growth rate. Coral growth is faster in the Gulf of Panamá now than in the Gulf of Chiriquí.

So, what does all of this mean?

In this situation, the scientists think that upwelling that happens in the Gulf of Panamá is acting as a buffer, keeping water temperatures cooler and more stable when they are increasing in other areas regionally. The coral reef in the Gulf of Panamá is benefiting from the cold water that upwelling brings. Rather than inhibiting the corals, it is protecting them. It ultimately implies that we may see less frequent coral bleaching events and healthier coral in reefs where upwelling occurs as ocean temperatures continue to increase. This also has implications for coral reef restoration and conservation efforts, since we may be able to better predict areas that will be more suitable for coral reefs in the future with the warmer water that will come with climate change.

Reviewed by: 

Jeannie Wilkening

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Elisabeth Lang

Elisabeth Lang

I recently graduated from Johns Hopkins University with a Masters degree in Environmental Science and Policy. My undergraduate education was at McDaniel College, where I majored in Environmental Studies and Biology. My undergraduate research focused on land use change and its impacts on biodiversity in Central America using GIS-based research. My graduate research examined potential sea level rise impacts on National Wildlife Refuges in the Mid-Atlantic region using GIS. I am currently working at the US Army Public Health Center where I analyze environmental samples. In my spare time, I enjoy traveling, reading, and running.

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