Symbiosis, the complex relationship where two different species mutually benefit from each other, remains one of nature’s least understood phenomena. Yet, it is a powerful evolutionary tool, allowing species to adapt and thrive in challenging environments.
Coral reefs are among the most vivid examples of symbiosis, and understanding this intricate partnership has become increasingly urgent due to the rapid decline of reefs worldwide caused by climate change.
Coral bleaching, triggered by rising ocean temperatures, has devastated reef ecosystems across the globe. Bleaching occurs when corals, stressed by heat, expel the algae living in their tissues. These algae are crucial as they provide food and colour to the coral through photosynthesis. Without them, corals are more vulnerable and often die if they cannot recover quickly.
Unfortunately, as bleaching events become more frequent, reefs lose their resilience. The Great Barrier Reef in Australia is one of the most visibly affected sites. According to the US National Oceanic and Atmospheric Administration’s Coral Reef Watch, around 54% of oceans with coral reefs have experienced severe heat stress, pushing these ecosystems to their limits.
To address this crisis, a global research initiative, the Aquatic Symbiosis Genomics (ASG) project, is using genomic analysis to understand and potentially safeguard coral reefs. Led by the Wellcome Sanger Institute and funded by the Gordon and Betty Moore Foundation, the ASG project aims to reveal the genetic mechanisms underpinning coral-algae symbiosis. By sequencing coral DNA, researchers hope to identify genetic traits that enhance coral resilience to rising temperatures and associated diseases.
“Coral reefs are called the rainforests of the seas for a good reason,” said Michael Sweet, of the University of Derby, and leader of the project. “They provide homes for a vast array of sealife and have an estimated global worth of around £6tn a year because of the fishing, tourism industries and coastal protection they support.”
This project has prompted innovative advancements in genetic research techniques. Coral’s hard, stony skeletons and the close integration of their genomes with algae present challenges in DNA extraction and separation. To tackle this, scientists have developed new methods to isolate the coral genome from that of the algae.
“At the current rate of bleaching, about 90% of the world’s coral reefs will be functionally extinct by 2030 and will no longer be able to support life,” added Sweet. “It is extremely worrying.”
This work has already yielded significant findings. For instance, several common coral species initially thought to be single species are now recognised as distinct ones. Moreover, researchers discovered that the algae’s genome is often twice as large as that of the coral itself, likely due to the complex process algae use to convert sunlight into sugars that nourish both partners.
“However, there is a great deal that we still do not know about symbiosis,” said Mark Blaxter, another research leader at the Wellcome Sanger Institute. “What happens to species when they go into symbiosis, what changes inside them and makes them different, and how do the two species collaborate?
“These are crucial questions that we need to answer quickly otherwise coral reefs are going to be destroyed in less than a decade.”
Once the scientists identify corals with genomes showing resistance to heat and disease, they plan to explore ways to enhance these traits across coral populations. This could involve breeding colonies from genetically promising samples or using gene-editing techniques to transfer these resilient traits to faster-growing coral species. Such modifications could help corals withstand higher temperatures and recover from bleaching, offering a potential pathway to protect these ecosystems.
“This is important,” added Sweet. “It means that some widespread corals thought not to be ‘at risk’ may be made up of local species, each of which could be vulnerable to climate change in different ways. This is the kind of data we need to collect.”
By decoding the genetic foundation of coral-algae symbiosis, scientists aim to empower conservation efforts to save reefs worldwide. This research could ultimately help restore the health of coral ecosystems that millions of marine species, and countless human communities, rely on for food, tourism, and coastal protection. The ASG project thus represents a hopeful step toward understanding and preserving one of nature’s most fascinating, yet endangered, partnerships.
“In this way, you can combine sets of characteristics so you can create a type of super-coral,” said Sweet.
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