Healthy coral reefs are a fundamental building block for thriving ocean ecosystems, and an invaluable form of natural coastal protection from extreme weather events. But corals and the unique reef ecosystems they create are at risk because of climate change. ReCoral by ØrstedTM is a project that sets out to discover whether offshore wind turbine foundations could provide an additional new home where corals have the potential to flourish.
The novel non-invasive method involves collecting coral spawn that washes up on the shoreline of the Penghu Islands, cultivating it in the laboratory, and then introducing viable coral larvae into mesh cages specifically designed to fit around turbine foundation pieces, with the intention that they will settle and grow there.
Why could turbine foundations hold a key to coral restoration?
In theory, the turbine foundations should provide a suitable environment for corals to thrive. Corals live in symbiosis with an algae called zooxanthellae that relies on sunlight for photosynthesis, meaning they must live near the surface.
But these algae can be badly harmed if the water becomes too warm, too polluted, or too often exposed by extreme low tides, resulting in coral bleaching. As the impacts of climate change accelerate, coral bleaching occurs more and more frequently in the shallow waters where corals live naturally.
On the turbine foundation, by contrast, the corals will have good access to light while being protected from extreme temperatures by the natural circulation of the cooler, deeper water the turbines stand in.
In practice, there are many challenges to overcome if corals are to make their home on offshore wind turbine foundations. ReCoral is an experiment grounded in laboratory-based trials and meticulous planning to explore the potential for offshore wind to deliver direct benefits for coral health and help them adapt.
The method needs to be tested and refined, and its impact measured and reported. Only then will we know whether ReCoral can be scaled up and used in other locations with similar habitat conditions.
The climate crisis is accelerating global biodiversity loss, threatening the ecosystems that support all life on earth, and nature’s own ability to regulate the climate.
As a leading renewable energy company, we’ve made the fight against climate change our core business through the deployment of green energy solutions.
But we want these solutions to do more than generate green energy. We want them to have a lasting positive impact on nature and people. Restoring coral reef ecosystems can contribute to achieving our goals for climate, people, and nature.
According to the International Union for Conservation of Nature, more than 500 million people around the world depend on coral reefs for food, storm protection, jobs, and recreation. We also depend on healthy natural habitats and wildlife, especially in our oceans, to provide natural mitigation and adaptation against the impacts of climate change.
We’ve set the ambition to achieve a net-positive impact on biodiversity for every new project we commission from 2030 onwards.
To make this a reality, we’re partnering with conservation experts and launching a series of pilot projects to find and test methods that enhance biodiversity and can be deployed at scale. ReCoral is just one of these pilots.
A novel, non-invasive, experimental coral restoration method
Our method begins on the shorelines of the Penghu Islands off the west coast of Taiwan. A marine biologist from Penghu Marine Biology Research Centre collects coral spawn that have been released in the annual mass spawning event trigged by a full moon in spring.
At the wind turbine foundation, the coral larvae are released into custom-made mesh cages that have been attached to the foundation with battery-powered electromagnets, one metre below the lowest tide level. This location allows the corals to receive adequate light and provides access for deploying the cages and monitoring the corals.
The larvae are left in the cages for 36 hours, giving them time to attach themselves to the foundation. After this, we remove the cage structures, exposing the corals to the surrounding water column and allowing them to grow.
This is a non-invasive method, meaning we take nothing away from existing coral ecosystems. Instead, we collect some of the billions of egg bundles released during the mass spawning event – so many that the water’s surface appears pink. Only some of these are fertilised and become larvae.
We collect the eggs from the shoreline with guidance from the Penghu Marine Biology Research Center and consent from local government. The eggs we collect are among those that wouldn’t otherwise survive. Collecting them therefore has no impact on the corals that originally released them, nor on the propagation of coral species.
In June 2022, we completed our first seeding trial, using coral spawn collected from the spring mass spawning event, and a mesh cage that we attached to one turbine foundation piece. Early monitoring shows that the corals did not achieve the growth rates we expected.
This first attempt allows us to refine our novel approach for the next trial. We gathered the following learnings:
- The coral spawning season began later than expected, perhaps as a result of rising water temperatures caused by climate change. This resulted in a very short window of time in which the technical crew could safely introduce the larvae to the mesh cage. In future trials, we will consider the impact of a changing climate on the complete lifecycle of the corals, including coordinating the dates of mass spawning event and the weather window for offshore operations.
- The real-life conditions faced by the corals in the mesh cage were more challenging than those they experienced in the laboratory, with larvae vulnerable to strong currents and competitive species. We will try to recreate these conditions more accurately before transplantation, or delay transplantation until the corals have reached a more resilient stage of their lifecycle.
- The mesh cages proved very difficult to install safely and efficiently at sea. This meant the technical crew was only able to install one out of four mesh cages, dramatically reducing the sample size for the experiment. We will therefore redesign the mesh cages to make installation easier, as well as improving the environment they provide for coral growth at different stages of maturity.
With these improvements to the methodology and equipment, we look forward to proceeding with a second trial with a tentative date of mid- 2023. We will continue to monitor both the first and future mesh cage installations.
We’re also excited to renew our collaboration with Penghu Marine Biology Research Centre as our key partner for continuous studies and coral monitoring in the Penghu Islands.
Ultimately, we hope to refine a method that can be deployed at a much greater scale than the trial at Greater Changhua offshore wind farms. If we are successful, this coral restoration method could be applied to the foundations of offshore wind turbines in any tropical waters around the world, boosting ocean biodiversity.
Turbine-born larvae as a lifeline for natural reefs
Corals growing on offshore wind turbine foundations would also release their own spawn, which could be carried by ocean currents to settle naturally elsewhere. This could boost genetic connectivity across oceans and support the restoration of existing coral reefs.
Larvae generated at offshore wind farm sites could also be captured, then transported to and released at naturally occurring reef locations.
In either case, restoring naturally occurring reefs would, in turn, support healthy stocks of fish and other reef species.
In the latest coral reef restoration guide released by the United Nations Environment Programme, the release of larvae is considered as ‘potentially one of the most scalable methods for coral reef restoration’.
Sharing findings with the coral conservation community
We will share what we find with the broader coral conservation community and with other wind farm developers. Halting and reversing biodiversity loss must be a collaborative effort so whether or not our pilot succeeds, we hope our findings will be useful for future endeavours in coral restoration.
Why does coral restoration matter?According to the United Nations Framework Convention on Climate Change (UNFCCC) and WWF, coral reefs are among the most diverse and valuable ecosystems on the planet.
But our oceans are heating up because of climate change. Temperature increases can induce coral bleaching, which threatens the survival of coral reef ecosystems.
The International Union for Conservation of Nature has designated coral an endangered species, with 75 % of corals worldwide predicted to face high to critical threat levels by 2100.
When coral populations suffer, so do the hundreds of thousands of marine species that live in coral reef habitats, and, in turn, the millions of people that depend on these species for their livelihood.
According to the International Union for Conservation of Nature, more than 500 million people around the world depend on coral reefs for food, storm protection, jobs, and recreation.
What's the difference between ReCoral by ØrstedTM and other coral reef restoration projects?
A range of coral restoration techniques are currently being developed in tropical waters around the world. These include:
- Coral gardening, which uses coral fragments to replenish deteriorated reef sites
- Growing corals on artificial reef structures
- Coral seeding, which involves spreading coral larvae on deteriorated reef sites
- Breeding more resilient corals in the laboratory before transplanting them onto reefs
Some techniques involve clipping sections of coral from a healthy reef to plant elsewhere, something that can damage the existing reef.
ReCoral is unique because we’re seeking to attach larvae to artificial reef structures – wind turbine foundations – in deeper offshore waters. This hasn’t been attempted before.
Weird and wonderful coral - what on earth is it?Corals are a truly unusual form of life. They’re animals that host a plant – microalgae – within their own tissue, with each part depending on the other for survival.
The animal part provides protection and nutrition for the microalgae, which, in turn, use sunlight to turn water and carbon dioxide into the oxygen the animal part needs to survive, using photosynthesis.
What is coral bleaching?Coral bleaching occurs when sea surface temperatures are 1.5 °C above the average for a prolonged period of time. This causes the plant and animal parts of a coral to disconnect from each other. Without the pigmented microalgae, the colour drains from the coral, which is also deprived of nutrition.
How do corals build a reef?Corals can grow calcium carbonate (CaCO3), which they use to build the hard structures which form coral reefs. These provide the foundation for entire ecosystems and protect coastlines from floods and storms.
How is coral spawning linked to moon phases?Under optimal conditions, corals release their spawn in a synchronised event following a full moon in spring, when temperatures are increasing towards the annual maximum.
During a full-moon phase, sunset occurs before moonrise, exposing corals to a period of darkness. This, followed by the predominantly blue light of the moon, is thought to trigger coral spawning.