The curious purpose that lurks behind the rare coloration of coral reefs

The curious purpose that lurks behind the rare coloration of coral reefs
Colorful coral bleaching at Acropora in New Caledonia. (Richard Vevers / The Ocean Agency / XL Catlin Seaview Survey)

Many coral reefs around the world are experiencing episodes of coral bleaching. This condition is caused by thermal stress due to spikes in sea temperatures during unusually hot summers. In many cases corals recover when water ceases to be so hot, but die when bleaching is severe corals die.

Once his living tissue is gone, the skeleton is exposed to erosion. In a few years, an entire coral reef can decompose and much of the biodiversity that depends on its complex structure is lost, a scenario that currently threatens the future of reefs around the world.

The same name of this condition is all ‘bleaching’, that is, corals become pale. However, some corals in a state of discoloration experience a mysterious transformation, emitting a range of different bright neon colors. Scientists from the University of Southampton’s Coral Reef Laboratory have studied this drastic and rare coloring change.

In their study, published in the journal Current Biology, the team reveals that this phenomenon is a sign that corals are struggling to survive.

Researchers conducted a series of controlled experiments at the University of Southampton’s coral aquarium facility. They found that during colorful bleaching events, corals produce what is effectively a layer of sunscreen of their own, showing themselves as a colorful screen. In addition, this process is believed to encourage coral symbionts to return.

Researchers believe that corals undergoing this process have likely experienced mild or brief warming episodes or ocean disturbances in their nutrient environment, rather than extreme events.

Scientists are hopeful of the report suggesting that there has been colorful bleaching in some areas of the Great Barrier Reef between March and April. They believe this increases the hope that, at least some areas of the world’s largest reef system, may have better prospects for recovery than others. Study researchers also emphasize that only a significant reduction in greenhouse gases on a global scale and sustained improvement in water quality at the regional level can save coral reefs beyond the 21st century.

Reference: ‘Optical Feedback Loop Involving Dinoflagellate Symbiont and Scleractinian Host Drives Colorful Coral Bleaching’. Elena Bollati, Cecilia D’Angelo, Rachel Alderdice, Morgan Pratchett, Maren Ziegler and Jörg Wiedenmann. Published Current Biology May 21, 2020 DOI: https: //doi.org/10.1016/j.cub.2020.04.055