Rise In Sea Levels Caused By Global Warming May Save Coral Reefs

First Posted: Aug 19, 2016 07:09 AM EDT

Coral reefs have been under threat from global warming. However, for some coral reefs, the rise in sea levels brought by the same global warming may just be what it needs. A new study of reefs revealed that although tides are the major cause of water mixing, experts have found that the increase in sea level may save the corals from bleaching.

Although reefs are essentially found in a much deeper part of the ocean, most tropical types of corals usually get a thin layer of water on them during low tide. Experts say that corals closer to land can trap small amount of water between them and the shore. Big effects can be seen when low tide coincide with the middle of a summer day. "You can think of it as applying the same heat to a smaller amount of water," Professor Ryan Lowe of the University of Western Australia, lead author of the study, told IFLScience.

The Telegraph reported that mounting levels of atmospheric carbon dioxide are thought to cause a considerable amount of changes to ocean temperature over the next 100 years which will increase the frequency and severity of mass bleaching, where corals eject the symbiotic algae living in their tissues, turning them completely white. According to the new study, sea levels are forecasted to rise by more or less 0.5-0.8m by the end of this century. The study said that this rise in sea levels brought about by the melting of polar ice caps will be good for the reefs since it could help improve the extreme temperature changes experienced by many shallow reefs.

The remote and iconic Kimberley region of Western Australia is not only home to some of the world's most ancient rock art, rare species such as the golden bandicoot, the scaly-tailed possum and the toe-tapping monjon, but also some of the world's strongest corals. Dr. Lowe explained that the Kimberly coast also boasts one of the world's most extreme tidal ranges, with the water height measuring more than 10m over each tidal cycle. When these tides combine with the reefs in the area, it converts into big temperature changes.

"Extreme temperatures are known to be one of the key stressors to coral reef communities around the world, and developing an improved understanding and ability to predict temperature extremes within reefs is critical to predicting the fate of reefs in the future," Dr. Lowe said. Dr. Lowe and his team wanted to find out what factors can control temperature changes within the shallow reef systems. To do that, they developed a physically based model to conclude temperature changes within tide-dominated reefs considering factors such as tides, solar heating cycles and reef structure, reported.

"By assessing reefs in the Kimberley and a number of other reefs around the world, we identified how the regular cycles of the tide and heating by the Sun interact to drive extreme temperatures, in many cases by over 6°C each day, and how even moderate increases in mean sea level can dramatically reduce these temperature variations by more than 50 per cent."

The findings suggest that even with the harsh predictions of ocean warming and rising sea levels, the tide-dominated reefs can have unexpected benefits from it. "While rising sea temperature from global warming will clearly have negative effects on reefs globally, these kinds of reefs should at least see a slight drop in the large temperature variations they presently experience," explained Dr. Lowe.

Meanwhile, future research are a must to how reef organisms will behave to changes in future temperature routines, focusing specifically on the acute effects of short-lived temperature extremes versus the longer term effects of sustained warming.

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