Assisted evolution: is meddling with corals the key to their survival?

Written by Eleanor Gilbert

In July 2018, a team of divers – biologists from the Gates Coral Lab at the Hawai’i Institute of Marine Biology – watched as corals spawned.  Using nets, they captured tiny eggs and sperm that were released into the water and brought them back to the lab.

The goal: to crossbreed coral species that successfully survived a recent coral bleaching event.  Coral bleaching, a heat-driven process, occurs when the water surrounding corals becomes too warm to sustain its relationship with small symbiotic algae that live within its tissues.  The corals expel these algae, ultimately ridding themselves of their primary food source, and turn white.  Many do not recover.  By crossing the survivors, scientists hope to create offspring that have a better chance of surviving warmer and more acidic oceans in the future.

A researcher surveys coral for signs of bleaching

This is one example of an upcoming conservation strategy known as “assisted evolution”, which attempts to accelerate the capacity of species to adapt to their changing environments.  Planet Earth is currently experiencing an era known as the Anthropocene, a period of unprecedented global change driven largely by human society.  Commonly known as “climate change”, this period of global transformation is rapidly altering the ocean environment at a rate that coral reefs are struggling to adapt to.  At present, corals are facing multiple environmental threats, from pollution and overfishing, but they are especially at risk from climatic changes that are being driven by greenhouse gas emissions.  To date, 40% of carbon dioxide (CO2) emissions – that’s 170 billion metric tonnes – has been absorbed by the oceans.  This makes the oceans more acidic, which causes coral reefs to dissolve and impedes their ability to accrete – that is, build – reef ecosystems.  As the planet warms, so do the oceans, and coral bleaching is becoming more frequent.

Bleached coral
Photo of bleached corals taken on the Great Barrier Reef between Port Douglas and Cairns in 2017. (Photograph: Brett Monroe Garner/Greenpeace)

The loss of worldwide coral reefs would have a catastrophic impact on our society.  While reefs make up only 1% of the ocean environment, they are home to one quarter (that’s over one million) of all marine species, including thousands of fish species which are a vital food source for many coastal communities.  Honduras, Madagascar, Indonesia and many Caribbean islands are heavily dependent on the tourism that coral reefs attract to boost their economies.  These reefs also provide crucial flood protection from storms in tropical areas around the globe.

Coral bleaching events are becoming more common and increasingly severe. The Great Barrier Reef experienced the first ever recorded back-to-back bleaching event following warming in 2016 and 2017, and huge sections of this fragile ecosystem – which stretches almost 1,400 miles – have died as a result.  Unsurprisingly, this has triggered a call for immediate and effective conservation action.  Many protection strategies already exist for the marine environment – Marine Protected Areas (MPAs), habitat restoration and reducing exploitation – however these tools are often inadequate solutions to cope with the rapidly changing oceans.

2016-2017 GBR bleaching
Coral bleaching in the Great Barrier Reef, Australia, in 2016 and 2017.  (Image: Arc Centre of Excellence for Coral Reef Studies)

Corals are capable of evolving to survive environmental pressures, however they are simply not evolving fast enough.  This is where assisted evolution strategies may come into play.  Selective breeding of “super strong” coral in a lab, engineered to possess the same tolerant characteristics as their parents, may help reef ecosystems to adapt faster to warming sea temperatures.  Alternatively, assisted evolution may also take form in moving individual corals from warmer regions of their habitat to cooler regions, in the hope that they might naturally pass on their ability to endure warmer waters to their offspring.  Rolling this strategy out on a universal basis may not work however, as hundreds of coral species exist, and some that have adapted to warmer waters over time may not respond well to temperature fluctuations in new locations.  This is where more significant changes, like artificially editing genes using tools such as CRISPR, may become useful.

Some scientists are wary of the controversy surrounding assisted evolution, and the application of these tools in place of more traditional protection strategies has sparked intense debate over the trade-off between the benefits and possible harm to coral reef ecosystems.  Promoting the survival of more tolerant species at the expense of more sensitive ones will eventually lead to a reduction in coral diversity.  As corals provide a vital structure that many species call home, a change in coral species could also affect the diversity of the animal and plant community that live on coral reefs.  More momentous changes, such as editing genes, could potentially have unforeseen and possibly damaging consequences.  The release of genetically modified corals and their algal symbionts into the environment may mean they are better “competitors” – meaning they are better at utilising the environment and resources at their disposal than natural populations – and therefore become invasive.  Unforeseen consequences are, by nature, difficult to predict, and as many of the proposed assisted evolution strategies have yet to work in nature these adverse impacts are still just speculation.

Human intervention
Human intervention may be the only thing that allows corals to evolve as fast as their changing environment

So, is meddling with coral reefs the key to their survival? Developing assisted evolution techniques may buy these ecosystems some crucial time to adapt to climate change.  On the other end of the spectrum, the power over natural evolution that we will gain from developing these assisted tools could easily transform our role from protectors to designers of these natural ecosystems.  And this begs the question – if corals (and other fragile habitats) can be engineered to adapt to climate change, then why should climate change be tackled at all? Ultimately, coral reefs worldwide are already experiencing rapid and irreversible damage as a result of climate change, and without immediate action the vast majority of coral reefs will be lost.  The debate over assisted evolution and whether, how and when it will play a role in coral reef protection needs to be solved for the sake of ecosystem conservation.

Eleanor Gilbert is an MRes Marine Biology student at the University of Plymouth and the Marine Biological Association.  She has a strong interest in cnidarian biology and evolution, and the focus of her masters project is post-bleaching recovery by symbiont uptake in adult anemones.  You can follow her on twitter here or get in contact with her via LinkedIn here or her email (

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