Offshore wind turbine foundations to aid coral restoration


A new safe haven concept

Giving corals a home among our tropical wind turbines

Coral reefs are home to more than a third of all marine fish species, while more than a quarter of all marine species use them as nursery grounds. But corals and the unique reef environments they create are at risk because of climate change. Our new project ReCoral by ØrstedTM sets out to discover whether offshore wind turbine foundations could provide a new safe haven where corals can potentially flourish

Near the Penghu Islands, off the west mainland of Taiwan,  we and our partners from the Penghu Marine Biology Research Center are preparing to take tens of thousands of coral larvae by boat to the foundations of four offshore wind turbines at the Greater Changhua offshore wind farms. If the larvae succeed in settling on the foundations, this could be the start of a completely new approach to coral restoration. 

For this proof-of-concept trial, surplus indigenous coral spawn will be collected from the shorelines of the Penghu Islands and incubated in a laboratory until they become viable coral larvae. After this, they can be taken to the wind turbine foundations, 35-60 km off the coast, and helped to settle there.

Ove Hoegh-Guldberg, Professor of Marine Studies at the University of Queensland in Brisbane, Australia
In times when we’re facing an unprecedented loss of natural coral reefs, the potential benefits offered by an initiative such as ReCoral are music to my ears. The foundations of offshore wind turbines will create new offshore habitat. This habitat may be located in thermal niches that offer a Noah’s Ark-type effect and, if scaled up, the ReCoral concept could potentially be utilised to support the long-term survival of coral species as well as the regeneration of naturally occurring nearshore coral reefs.
Ove Hoegh-Guldberg Professor of Marine Studies at the University of Queensland in Brisbane, Australia
Our biodiversity agenda

We’re working to create a net-positive biodiversity impact  for all new renewable energy projects we commission from 2030. As one of our priority areas of work, we’re developing a suite of biodiversity-enhancing measures that the scientific community can stand behind.

The innovative ReCoral initiative complements this work by seeking to develop a completely new approach to coral restoration. 

If the trial is successful and can be scaled up, our hope is that large numbers of larvae from subsequent generations of coral will be carried by ocean currents away from our offshore wind farms and settle on naturally occurring reefs, helping them to thrive. 

Visual simulation of coral growing on wind turbine foundations

An experimental method

The method we’re using has never been tried before. We can’t be sure it’ll be successful. But we’re committed to finding new ways of making a positive contribution to biodiversity.

Early tests and input from the scientific community suggest that the potential rewards of this project vastly outweigh the risks. And if the proof-of-concept trial is successful, we’ll look to scale up the method. We’ll make our findings public so that others can do the same.

"Naturally, given its novelty, the developers of this bold initiative have a number of significant challenges to tackle as they look to progress beyond their proof-of-concept trial towards a fully scaled-up deployment. It is encouraging to see, however, an industrial player collaborating with academics and environmental NGOs in an effort to secure the kind of ambitious and large-scale outcomes that are required”, says Ove Hoegh-Guldberg, Professor of Marine Studies at the University of Queensland in Brisbane, Australia

Hywel Roberts
The ReCoral project has such significant potential. Working to realise this innovation initiative has been one of the most exciting experiences of my career to date.
Hywel Roberts Strategic Environment & Permitting, Ørsted

Why is it important to care for coral?

On this Earth that we call home, we depend on our neighbours

We share our home, planet Earth, with around nine million other known life forms. Between us, we live in some interesting places.

An endangered species many of us depend on

According to the World Wildlife Fund, 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. 

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.
The International Union for Conservation of Nature has designated coral an endangered species

More than 500 m people worldwide depend on [coral reefs] for food, storm protection, jobs, and recreation

International Union for Conservation of Nature

Want to learn more about coral reefs? Dive into the details 
  • 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 are corals 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. 

What’s the science behind our ReCoral project? 

A deep, cooling water column

Coral occurs naturally in such shallow waters that high surface temperatures can cause coral bleaching. 

But in the deeper waters where offshore wind turbines are installed, a much more stable temperature is maintained, thanks to the circulation between the warmer water at the surface and the cooler water from below. 

The foundations of offshore wind turbines provide a unique environment where corals can grow close enough to the surface to receive enough sunlight, but without being exposed to high temperatures. This limits the risk of coral bleaching. 

Area of seawater around wind turbine foundations that has optimal sunlight penetration and temperature for coral

A non-invasive approach 

Our approach to larvae sourcing is non-invasive. We only collect surplus coral egg bundles that wash up on shorelines, rather than removing anything from existing coral ecosystems.  

Corals release billions of eggs – so many that they colour the water’s surface pink. Only some of these are fertilised and become larvae. The eggs we collect from shorelines 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.  

Coral spawn colouring the sea pink
Want to learn more about the ReCoral approach? Dive into the details 
  • How  do we collect the eggs, nurture them in the lab, and help them attach to the wind turbines?
    Plastic collection cup used for coral spawn collection

    A marine biologist collects coral spawn at the shoreline using a plastic cup, entering the water at depths of up to 0.5 m to avoid collecting coral spawn that’s been washed over the sand, as this could affect its viability.  

    Collected coral spawn is then incubated in rearing containers in an onshore laboratory. On day five of incubation, we check how many eggs have created viable coral larvae.  

    At the wind turbine foundation, the coral larvae are released into custom-made seawater enclosures that are attached to the foundation with magnets. Neoprene sealing lines the enclosure, and a mesh cover allows the enclosures to be replenished with the surrounding seawater. 

    The larvae are left in the enclosures for four days, giving them time to attach themselves to the foundation. After this, we remove the mesh cage structures, exposing the coral to the surrounding water column and allowing them to grow. 

    For the seeding of coral larvae in the proof-of-concept trial, 1 m2 areas on four separate foundations will be used. The areas will be positioned 1 m below the lowest tide level. This will ensure that the corals are submerged by water, receive an adequate amount of light, and are accessible for deployment and monitoring purposes. 

  • 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 by ØrstedTM 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.  

  • What other biodiversity-enhancing initiatives has Ørsted implemented? 
    We’ve created boulder reefs at Anholt Offshore Wind Farm in Denmark, installed cod pipe reefs at Borssele 1 & 2 Offshore Wind Farm in the Netherlands, and partnered with WWF Denmark to support marine biodiversity and the cod fish stock in the Kattegat straits in Denmark.
Fisheries Research Institute, COA
We're excited to be working with the world's leading offshore wind developer on this great initative
Hern-Yi Hsieh Director, Penghu Marine Biology Research Center

How much could marine life benefit in the long term?

Expanding to grow coral across a wind farm site

If the proof-of-concept trial on four wind turbines is successful, our next step is to develop a method where the concept can be applied to a larger area on another wind farm project.

Ultimately, the concept could be applied to offshore foundations of any kind in tropical waters around the world, boosting biodiversity. 

Alasdair Edwards
This bold attempt to find out whether offshore wind turbine foundations can be seeded with baby corals, which will hopefully grow into viable spawning populations within a few years, is technically challenging. If the ReCoral methodology is scalable, the turbine foundations could provide refugia for corals relatively safe from the marine heatwaves that are increasingly killing corals as global warming proceeds. I look forward to seeing the results of this trial in due course.
Alasdair Edwards Emeritus Professor of Coral Reef Ecology at Newcastle University

Turbine-born larvae as a lifeline for natural reefs

Mature corals successfully thriving on offshore wind turbine foundations will release their own spawn, which could be carried by ocean currents to settle naturally elsewhere. This could boost genetic connectivity 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, larvae release is considered as ‘potentially one of the most scalable methods for coral reef restoration’.  

Restoring coral reefs supports healthy stocks of fish

Sharing findings with the coral conservation community 

We’ll share the techniques we develop and the lessons we learn with the broader coral conservation community and with other wind farm developers. Whether or not our pilot succeeds, our findings will be useful for future endeavours.  

As ReCoral is an innovative scientific project, there’s an inherent risk that it won’t work. To address this, we’ve implemented a range of risk mitigation measures.

ReCoral timeline

Summer 2021
Laboratory testing in Taiwan 

Collection of surplus coral spawn from the coastlines of the Penghu Islands and pilot test in an onshore laboratory and at a quayside test facility. Confirmation that coral larvae will attach to metal structures. 

Winter 2021
Team in northern Denmark tests habitat prototypes 

Detailed design and test of prototypes for the temporary habitats – mesh cage structures – in which coral larvae will be installed on the wind turbine foundations. Fabrication of these structures. 

April-August 2022
Proof-of-concept trial begins in Taiwan 

Net-cages are transported from Denmark to Taiwan. Coral spawn is collected, incubated at an onshore laboratory, and subsequently released onto four wind turbine foundations at the Changhua offshore wind farm site in the Taiwan Strait. Initial monitoring is conducted to determine whether coral have successfully settled. 

Map showing journey of net cages transported from Denmark to Taiwan for ReCoral project
Map showing ReCoral project set-up in Taiwan

ReCoral: Standard Operating Procedures

Download our how-to guide for implementing ReCoral

Watch our ReCoral video

See the ReCoral concept and process in action

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Biodiversity is our life support system – and it’s in crisis. Find out more about our biodiversity strategy