Temperature increases from climate change can cause substantial damage to coral reefs. Coral are animals that form hard structures of calcium chloride, similar to the shell of a crab. These structures house coral colonies, as well as the algae that provides food for the coral. If local water temperature rises, the coral will expel the algae, losing a major source of energy. This event is called “bleaching”, and it has been recorded in the U.S., Southeast Asia, and the Great Barrier Reef (GBR) near Australia. To combat this ecosystem-destroying event, scientists in Australia, like Dr. Saskia Jurriaans, have developed a method to restore reefs, known as coral IVF. This technique consists of growing baby corals in specialty pools, and returning them to the reef of interest. For a transcript, please visit https://climatebreak.org/breeding-heat-resilient-coral-to-restore-at-risk-coral-reefs-with-dr-saskia-jurriaans/.
As ocean temperatures increase due to climate change, an emergent crisis known as coral bleaching is on the rise. Coral bleaching poses the largest threat to coral reefs, which are some of the most diverse ecosystems in the world. Coral reef habitats occupy less than one percent of the ocean floor, but constitute more than 25% of all marine life, providing habitats for a vast array of species from small organisms to large fish and sharks. Additionally, biodiverse reefs provide a variety of economic benefits, supporting jobs, tourism, and fisheries. Reefs also protect lives and property in coastal areas, absorbing 97% of a wave’s energy while buffering against currents, waves, and storms.
However, when ocean temperatures rise, corals become stressed and expel the marine algae living inside their tissues, known as zooxanthellae. Typically, coral live synergistically with zooxanthellae, meaning the algae provide food for the coral while the algae use the coral as shelter. Due to stress, corals expel zooxanthellae, causing them to become a white skeleton. If the temperatures remain high, the coral won’t allow the algae back and the coral will die. Once corals die, reefs rarely come back. As climate change progresses with its warming trend, corals endure greater stress, and experience longer and more intense bleaching events. Between 2014 and 2017, 30% of the world’s reefs experienced heat-stress leading to coral bleaching. In 2005, the US lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. Fortunately, marine biologists have been working on a new strategy to restore damaged coral reefs, known as Coral IVF (in vitro fertilization), which entails taking healthy coral eggs and sperm, crossing them in a supervised pool, and returning the mature coral to a damaged coral reef. Importantly, IVF coral are often bred to be resilient to heat-induced bleaching, making Coral IVF a successful strategy in fortifying reefs against bleaching.
Coral IVF begins with biologists collecting spawn, or coral eggs and sperm, from heat-tolerant corals that have survived coral bleaching events. With these spawn, biologists can rear millions of baby corals in tanks and coral nursery pools before repopulating damaged reefs for restoration. So far, coral IVF has proven successful. The Great Barrier Reef (GBR) Foundation planted 22 large colonies of new baby corals off Heron Island in 2016. Four years later, the researchers found that the corals had survived a bleaching event and grown to maturity. The next year, the corals had reproduced and spawned babies of their own.
In 2016, 81% of the northernmost section of the GBR was severely bleached, including mass bleaching in other sections. The GBR provides an estimated economic value of $56 billion, including 64,000 jobs stemming from the reef. Losing the reef would be a major economic loss for Australia, which has already lost 50% of its coral since 1995. With coral IVF, there is hope for an eventual repopulation of the reef with healthy corals. Beyond the GBR, coral IVF is taking place in reefs across the US, Mexico, and the Caribbean. Approximately 90% of IVF-created corals survived 2023’s heat wave, holding on to the algae that sustain them.
Coral IVF not only mitigates short term reef loss, but also strengthens reefs in the long term. One study revealed that corals in the GBR that survived bleaching in 2016 had twice the average heat tolerance the following year. Research reveals that corals can pass on their adaptive strategies to their offspring. Experiments also reveal that heat-adapted corals can thrive in new environments and be an important source of reef regeneration globally. This technique can therefore be applied to any coral population. Further, the IVF process also can be done quickly, allowing scientists to respond to coral damage in an emergency.
Unfortunately, climate change still poses a threat to IVF created coral reefs. By 2049, annual bleaching events will become the norm in the tropics. Research reveals that as global temperatures rise, coral will become less tolerant to heat related stress. In Australia, there has been a massive bleaching event every other year for six years. Due to the frequency of such events, coral's ability to reproduce is compromised for a number of years. As global emissions continue to rise, temperatures will continue to rise, inducing further heat-related stress. Eventually, coral may not be able to live in excessively hot ocean waters. Coral IVF is an effective strategy to prepare corals for future temperatures, but likely only up to a certain point.
Dr. Saskia Jurriaans is a marine scientist working on the Reef Restoration and Adaptation Program, a multi-organizational partnership between the Australian Institute Of Marine Science, Commonwealth Scientific and Industrial Research Organisation, and others. On her team, she optimizes coral breeding techniques, as well as developing asexual coral reproduction methods to support the Great Barrier Reef.
For a transcript, please visit https://climatebreak.org/breeding-heat-resilient-coral-to-restore-at-risk-coral-reefs-with-dr-saskia-jurriaans/.
Ethan: I’m Ethan Elkind, and this is Climate Break. Climate solutions in a hurry. Today’s proposal: Building resilient coral reefs with heat resistant coral. Dr. Saskia Jurriaans, a scientist with the Australian Institute of Marine Science, describes how climate change can cause coral to eject the algae that provide them food in an event called bleaching.
Dr. Jurriaans: Coral reefs are bleaching when the temperature gets too high and the corals lose the symbiosis that they sustain with symbiotic algae. The bleaching per se is not necessarily the death, but if this is sustained over a longer time, then this will mean that corals die. You lose your fish population, people lose their food source, people lose their coastal protection from waves and all these hydrodynamic actions.
Ethan: Scientists have opted to breed coral that can be implanted back into the ecosystem, a process known as coral IVF.
Dr. Jurriaans: You'll select corals that have survived through these heat events. And if you cross these survivors with each other, you would get heat tolerant corals. You need to put a few of them in the system across certain reefs, and then they will cross with the natural population, and you will create more capacity, more resilience in the reef.
Ethan: To increase the scale of coral IVF, reef restoration projects in Australia have turned to indigenous communities that have a history of reef stewardship.
Dr. Jurriaans: With our current project, one of the ways of upscaling is to get the indigenous community rangers, and so we’re training them up so that they can actively do coral spawning, plant out these coral babies back on the reef. We are actively involving them in the process and collaborating with them.
Ethan: To learn more about coral reef restoration strategies, visit climatebreak.org.