coral reefs

Underwater view of the waves breaking over a healthy coral reef and reducing wave power at the shoreline, which can cause flooding. Image: Curt Storlazzi, USGS


The inertia

In the years 2015 and 2016 The Chagos archipelago of the British Indian Ocean Territory recorded unusually high water temperatures every 12 months. In 2015, the heatwave lasted eight weeks. Researchers studied the seafloor and found that living, healthy coral cover had decreased by 60 percent as a result.

When the same season happened in 2016, the region was again affected by unusually high sea temperatures, which lasted four full months. The seabed was not re-measured immediately after this second ocean heatwave. However, data from the Peros Banhos Atoll show that 68 percent of the remaining coral was bleached and 29 percent died. In successive heat waves of the ocean, more than two-thirds of the hard corals that formed the basis of one of the ocean's most important ecosystems have been extinguished.

This feels and sounds like another discovery of the bleak climate change just because of this information, but it turns out that the researchers studying the region have found a positive twist within a phenomenon that is not unique to this small area in the middle In the Indian Ocean: While the second heat wave killed more corals and the overall impact was dramatic between 2015 and 2017, in the second heat wave in 2016 far fewer corals were killed. The researchers actually believe that the resilience of existing corals could be high A key to protecting reefs around the world.

"It is encouraging that reefs have a degree of natural resilience, although further research is needed to understand the mechanisms by which some corals can protect themselves," says Catherine Head of the Zoological Society of London. "This could be our best hope to save these vital habitats from the catastrophic effects of climate change."

In 1998, similar heat waves ejected corals in the same region, and it took them a full decade to recover. This is actually a fairly quick recovery, which suggests that the reefs in the archipelago are uniquely resilient. The 2015-2016 event did not provide the same period for recovery, and data for 2019 suggest that another series of high temperatures could continue the attack on coral, but researchers still see the area as a tool to move forward learn how to protect them.

"We know that in the past it took about 10 years for these reefs to recover, but with increasing global temperatures, there are more and more frequent violent heat waves that affect the reef's ability to recover," says Head. "Our data shows that the 2016 event was worse than 2015, but did less damage. We think that's because the 2015 heatwave killed the more vulnerable species and those who survived were more tolerant of hotter temperatures. "