Ocean Warming and Coral Reefs: New Research With Unexpected Results

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Ocean Warming and Coral Reefs: Systematic and Comprehensive Study

The Belize Barrier Reef System was monitored in this study. Photo by chuck.taylor.

A new study, published in Nature Climate Change on the 8thof July 2012, investigated the effect of increases in Sea Surface Temperature on coral reefs in detail.

The research was performed by scientists from the Department of Marine Sciences and the Curriculum for the Environment & Ecology at the University of North Carolina at Chapel Hill; other partners of the study were the Department of Biological Science at the University of South Carolina and the Research Centre in Biodiversity and Genetic Resources of Porto University (Portugal).

This research monitored the effect of the rising SST on corals from different parts of the reef; near shore, back reef and fore reef colonies were considered. The near shore colonies are the ones closest to the coast, the fore reefs are those further away, and the back reefs are in between.

The species the scientists studied was Siderastrea siderea, the massive starlet coral; researchers correlated variation in the skeletal growth with increasing seawater temperatures. The timescale considered was between 1982 and 2008.

Coral More Resilient Than Expected

Dr. Karl Castillo, the lead scientist in this study, explains and comments on the findings.

We monitored corals on the Belize Barrier Reef System off the coast of Central America, considering reef habitats located across a range of distances from the coast. Our results showed that corals from different zones of the reef system have been affected differently by warming seawater temperatures.

Quite surprisingly, we found that corals located furthest from the mainland have shown a decrease in the skeleton growth; at the same time, however, the ones more proximal to the coasts have shown relative stability in skeletal growth. We expected that corals closest to the shore and thus exposed to more threats from the coast (i.e. pollution) would be most affected by recent warming since local stressors have been shown to reduce coral resistance and resilience. However, we observed quite the opposite trend. Corals located furthest from the coast have been most affected most by recent warming.”

Coral Reactions to Warmer Sea Water: The Reasons for the Difference

The reason for this different and unexpected behavior is not completely clear. Dr. Castillo says: “We think that the corals located closer to the coast are exposed to generally higher and more variable seawater temperatures; this may have caused the corals to become more resistant to recent warming.”

Ocean Warming and Coral

Does this mean that rising ocean temperatures won’t affect the corals near shore? Unfortunately not. As Dr. Castillo told Decoded Science, “This does not mean that near shore corals are not or will not be affected by rising seawater temperatures. It simply means that, for this particular coral species, in this geographical area, and over the study interval, we did not detect a decline in coral skeletal growth with recent rise in seawater temperatures.”

Additional studies, covering multiple species of coral, would be necessary in order to reach any general conclusions regarding the effect of ocean warming on corals.

Resources

K.D. Castillo et al. Decline of forereef corals in response to recent warming linked to historical thermal exposure. (2012). Nature Climate Change. doi:10.1038/nclimate1577. Accessed July 15, 2012.

Environmental Protection Agency. Coral reefs protection: what are coral reefs? Accessed July 15, 2012.

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