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Investigating coral bleaching to save ‘rainforest of the sea’


Warming oceans can break an important relationship: how corals and their relatives are controlled by their algae to look for the light. The discovery can inform efforts to save coral reefs, which in turn would benefit biodiversity and the human economy too!

In 10 seconds? A discovery into how coral-like sea creatures sense light can explain why coral reefs get into mortal danger when they are "bleached" due to warming waters or acidity. It also can direct scientists to a solution that can make the coral reefs – the rainforests of the seas – more resilient. (Read the science)

Bleached corals

Corals sense the light?! How? Well, yes because light is important to keep them alive. Corals (a bunch of tiny animals, or polyps stuck together under the sea)live in symbiosis with algae. They penetrate the coral cells, photosynthesise there and provide them with 90% of the energy they need. But due to climate change, sea temperatures and water acidity rise and the algae get ejected. As a result, the corals turn white – get bleached – and without food, fade away. This endangers the extremely rich biodiversity and sea life around them. On top of that, it affects the livelihood of local fishermen and people living off the tourism industry. (More on how bleached reefs affect fish)

So, what’s the discovery that can help save them? 
Well, my team has been studying a similar sea animal, the anemone Aiptasia, and we discovered that when it gets bleached, it loses the ability to crawl towards the light. On the other hand, that normal, healthy anemones actively move towards the light, suggesting their symbiotic plants in a way controlled them. This could be because the algae sense the light, need to increase photosynthesis and influence the animal to move towards it. (Read the paper)

OK, but why don’t you study this on corals directly? 
Because they are difficult and slow to grow in the lab. However, the anemone Aiptasia grows very fast – this is why it's the scourge of many fish tank enthusiasts, who consider it a pest. It's a curious sea animal resembling flowers and its body is made up of a cylindrical stalk, which it attaches to shells or rocks on the seafloor. But the reason why it's interesting, is because it's closely related to corals and jellyfish. (Find out more)

And how did you come to the discovery? 
We grew anemones in the lab in a normal state with algae living inside them and in a bleached state without any algae. We kept the bleached ones alive by artificially feeding them with brine shrimp. By comparing the two groups, we discovered how the algae affected the animal’s behaviour. We compared the movement of normal and bleached anemones and found that the ability to move towards the light was lost when they were bleached. We also compared movement towards light by pairing anemones with different types of algae to see if the same behaviour always occurred. (Read more here)

But how can this help save corals and coral reefs? 
Well, a happy relationship between the algae and the animal host is crucial in preventing coral bleaching. One idea to save corals is to transplant more thermally resilient algae into them and thus create so-called "super corals" that can survive heatwaves. Understanding how the algae and their host interact — including the ability to sense and move towards the light — will help researchers in their quest to save the algae-coral relationship in warming ocean waters and safeguard the precious biodiversity of coral reefs. (Find out more)


How to engineer super corals?

As marine heatwaves are projected to occur annually, the fate of coral reef ecosystems does not look good.

Creating thermally tolerant corals is one way to ensure they survive.

Several methods have been proposed such as breeding special corals adapted to hotter water and raising algae in hotter conditions to create more heat-tolerant strains.

More recently, gene editing in the reef-building coralAcropora was demonstrated.

This suggests that genetically modified coral may be a possible way to help corals cope with a rapidly changing climate, withstand heat stress and prevent bleaching.

(Psst, Shawna distilled 10 research papers to save you 1102.6 min)


Dr Shawna Foo

Written by Dr Shawna Foo

Postdoctoral research scientist at Arizona State University, using remote sensing to improve coral restoration outcomes, ridge-to-reef impacts on coral reefs, adaptive potential of marine invertebrates to climate change