An experiment in Palmyra Atoll National Wildlife Refuge collects coral larvae, allowing researchers to enumerate the number of baby corals settling on a reef. Recent research shows that corals are establishing new reefs in temperate regions as they retreat from increasingly warmer waters at the equator. Credit: Courtesy of Nichole Price | Bigelow Laboratory for Ocean Sciences

Climate change is causing a significant shift in coral reef populations as warmer ocean waters drive them away from the equator, a new scientific study has found.

The study, published this month in the journal Marine Ecology Progress Series, found that young corals on tropical reefs have declined 85 percent over the past four decades, while they have doubled in subtropical waters.

Climate change is the “greatest global threat” to coral reefs as mass coral bleaching and disease outbreaks become more common as the ocean warms, according to the National Oceanic and Atmospheric Administration. But as the coral reefs come under increasing pressure from climate change, they are finding new opportunities to thrive in a changing ocean environment.

“Climate change seems to be redistributing coral reefs, the same way it is shifting many other marine species,” said Nichole Price, a senior research scientist at Maine’s Bigelow Laboratory for Ocean Sciences and the lead author of the paper. “The clarity in this trend is stunning, but we don’t yet know whether the new reefs can support the incredible diversity of tropical systems.”

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Researchers have suspected that warming oceans are causing populations for many species to move beyond their traditional ranges in search of more suitable environments and food.

New data released this month by University of Maine scientist Rick Wahle showed baby lobsters are appearing in higher numbers off Atlantic Canada as below average numbers were found in the Gulf of Maine from Bar Harbor to Cape Cod. The warming Gulf of Maine is believed to be driving the endangered Atlantic right whale farther afield in search of food.

Now that appears to be the case as well with corals as subtropical waters become more favorable to them than the equatorial waters where they have traditionally thrived, according to the study.

Questions remain about the impact of this shift. The new subtropical reefs could provide a refuge for species under increasing stress from climate change, the study suggests. But what’s unknown is whether species, such as coralline algae, crucial to the survival of young coral are making the move into subtropical waters or whether young coral can thrive in without them, according to the study.

The composition of the new reefs is unknown, because of the expense of collecting genetic and species diversity data.

“So many questions remain about which species are and are not making it to these new locations, and we don’t yet know the fate of these young corals over longer time frames,” Price said. “The changes we are seeing in coral reef ecosystems are mind-boggling, and we need to work hard to document how these systems work and learn what we can do to save them before it’s too late.”

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Price and her team examined latitudes up to 35 degrees north and south of the equator and found the shift of coral larvae away from the equator mirrored on both sides. The researchers, who came from 17 institutions in six countries, compiled a global database of studies dating back to 1974, when record-keeping began, which they hope scientists will continue to add to and document the change in coral reefs over time.

“The results of this paper highlight the importance of truly long-term studies documenting change in coral reef communities,” said Peter Edmunds, a professor at the University of California at Northridge and a co-author of the paper. “The trends we identified in this analysis are exceptionally difficult to detect, yet of the greatest importance in understanding how reefs will change in the coming decades. As the coral reef crisis deepens, the international community will need to intensify efforts to combine and synthesize results as we have been able to accomplish with this study.”