Coral Species in Red Sea Barely Growing, Thanks to Global Warming

A CT scan showing slow coral growth of a coral species in the Red Sea.

Guest bloggers Andrea Donsky and Randy Boyer are co-founders of

Global warming is wreaking havoc on plant and animal populations around the world: Polar bear habitats are melting, giant trees in Yosemite are thinning, and branched coral in the Caribbean has been largely killed by bleaching due to warmer water temperatures. Now researchers believe global warming is also responsible for slowed growth of one species of coral in the Red Sea.

A new study published in Science and conducted by researchers at Woods Hole Oceanographic Institution (WHOI) used CT scans to determine that growth of diploastrea heliopora coral has dropped by 30 percent, and they fear it could stop growing altogether by 2070, if not sooner. Global Warming Directly Related to Slowed Growth
Summer water temperatures in the Red Sea are about 1.5 degrees Celsius higher than the ambient temperature in the past 10 years. In a WHOI press release, Neal E. Cantin, a WHOI postdoctoral investigator and co-lead researcher on the project, says the warmer sea temperatures are a direct result of global warming:

The warming in the Red Sea and the resultant decline in the health of this coral is a clear regional impact of global warming. [In the 1980s] the average summer [water] temperatures were below 30 degrees Celsius. In 2008 they were approaching 31 degrees.

But the discovery that the coral is at risk of disappearing came as a surprise to researchers, because bleaching, the typical sign of a problem related to warmer sea temperatures, is not occurring in the Red Sea. As WHOI Research Specialist Anne L. Cohen explains,

The corals look healthy, but looking inside at the skeleton gives you an idea of things to come. It's like osteoporosis. You look at a person and, on the outside, everything seems fine, but inside there are signs of trouble.

According to the researchers, the coral have been under chronic stress for a decade, and their rate of growth was lowest in 2008.

Innovative CT Scan Revealed Stress
The process of using CT scans to examine the skeletal structure of coral was used by Cohen and WHOI graduate student Casey Saenger in the Atlantic. But it was Cantin who adapted the imaging software to use on coral research in the Red Sea, allowing the skeletal structure of the coral to be examined without cutting into the skeleton, which is required for an x-ray examination of the growth bands (similar to tree rings).

Using the CT scans, researchers discovered two high-density growth bands, indicating high thermal stress, from 1998 and 2001. After 1998, skeletal growth dropped significantly and has been declining ever since.

The problems stem from a loss of algae in the coral tissues. When photosynthesis occurs in algae the coral gain energy, which helps them produce new skeleton. But thermal stress leads to algae loss, Cohen says:

When the corals are thermally stressed, they lose algae and many will eventually starve and die. When corals lose enough algae, they actually turn white, and that's what bleaching is. We think these corals are on their way to bleaching.

Only One Coral of Many
This study is just the tip of the iceberg, a study of just one species of coral, explains Cohen:

It's an important reef-building coral in the Red Sea, but there are about 250 species of stony corals in this region and we have no idea what the other species are doing. Some might be doing much worse; some might be doing a little better in terms of thermal tolerances. We need much more of this type of work to be able to predict what the coral reefs will look like over the next few decades.

Whether other species are doing better or worse, one thing is certain: D. heliopora coral's future looks bleak.

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Tags: Conservation | Global Climate Change | Global Warming Effects | Oceans

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