Corals creating own sunscreen for protection against rising sea temperatures, scientists say

James Marshall
May 23, 2020

Unfortunately for them, even the slightest increase in water temperature can be fatal for their relationship by expelling algae from the coral's tissue and revealing its white and vulnerable skeleton.

Corals are way more important than most of us are aware and should be preserved. But why didn't all corals suddenly become more colourful?

This funky display, captured on video by underwater drones, is a way of encouraging the algae, which provide coral with a crucial energy source, to return. And why did they only seem to appear during certain bleaching events? The new analysis, revealed on Thursday within the journal Current Biology, discovered that some coral produces its personal "sunscreen" layer with a goal to entice algae to return. When corals lose their algae due to stress, the excess light travels back and forth inside the coral tissue, reflected by the white skeleton.

In healthy corals, much of the sunlight is absorbed by the photosynthetic pigments of the algae.

"However, if the coral cells can still carry out at least some of their normal functions, despite the environmental stress that caused bleaching, the increased internal light levels will boost the production of colourful, photoprotective pigments".

Once returned, the algae starts using the light for photosynthesis, light levels inside the coral drop and the coral cells lower the production of the colourful pigments.

The corals, too, began to discharge the photosynthetic algae inside their tissue. For that, tackling world warming and enhancing the well being of the world's oceans is the one means, the scientists mentioned.

Colorful corals may be calling crucial algae back home
This Eerie Neon Glow Coming From Bleached Coral Could Actually Be Good News

"It has been long known that not all bleaching events are the same and a "patchiness" of the bleaching response has been observed frequently", he added. "These data are in excellent agreement with the conclusions of our controlled laboratory experiments, suggesting that colourful bleaching occurs in association with brief or mild episodes of heat stress".

But, with little known about how "genetics, symbiotic microorganisms and environmental factors" work together to influence coral bleaching, Katie Parker, a research assistant at Shedd Aquarium, said scientists chose to investigate how some coral reefs are able to survive extreme temperatures, while others from the same species can not. That's why we only see bright neon colours in particular bleaching episodes, when conditions are just right.

Other species of the coral community can display different colors during those episodes of bleaching. The variants of colors have evolved to allow species lots of strategies to cope with light, depending on their region. Within a few years, an entire coral reef can break down and much of the biodiversity that depends on its complex structure is lost - a scenario which now threatens the future of reefs around the world. But why didn't all corals turn so colorful?

Ghostly white coral reefs are one of the defining images of our drastically changing natural world, but a new study has shown that not all suffering corals turn pale when they are bombarded by pollution and rising ocean temperatures - some glow with stunning colors and vivid vibrancy.

Reports suggest that colourful bleaching occurred on some parts of the Great Barrier Reef in March and April 2020, so some patches of the world's largest reef system may have better prospects for recovery after the recent bleaching. "However, in most cases there are some corals that bleach white due to the involved color polymorphisms, so quite likely, observers will realize that something is wrong", Professor Jörg Wiedenmann, head of the University of Southampton's Coral Reef Laboratory, told IFLScience. Together, these actions can secure a future for coral reefs.

This article is republished from The Conversation under a Creative Commons license.

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