How restoration can help coral reefs June 28, 2024

Reef restoration methods are used to slow down reef decline and help speed up the natural recovery of corals. Here are two examples of propagation (Nicholas SHEARMAN)

By AFP - Agence France Presse

How restoration can help coral reefs

Record sea temperatures are bleaching coral reefs around the world and putting a new focus on attempts to restore these important marine ecosystems.

Here's an overview of how coral restoration is being done around the world:

- How is coral obtained? -

Restoration begins with obtaining the coral, sometimes by breaking up a healthy reef. These pieces can be broken into smaller pieces in a process called microfragmentation.

Each piece can become a new coral.

Another option involves collecting "fragments of opportunity" - pieces of coral broken off by natural causes, such as storms.

Conservationists can also propagate from egg bundles collected during reef spawning, although this is perhaps the most difficult approach.

Spawning is brief, usually occurring only once a year, and is affected by many factors, including moon phase and water temperature.

- What happens next? -

Coral micro fragments usually go to a "nursery" until they become robust enough to be transplanted to an existing reef or artificial structure.

Opportunity fragments are treated similarly. If they are large enough, they can be transplanted directly onto natural or artificial reefs.

The bundles of coral eggs and sperm collected during spawning will develop into larvae that can be installed on reefs or, more commonly, grown on artificial foundations before being transplanted to their final homes.

- What else is involved? -

Other techniques are used to enhance coral restoration, including mineral accretion technology.

This involves sending a low-voltage electric current through seawater to stimulate the dissolution and crystallization of minerals in artificial reef structures, accelerating coral growth.

The technique has had mixed results, with some studies reporting better growth and more resistant corals, but others finding no significant benefits.

Other interventions include stabilizing the substrate, which supports the reef foundations, and removing algae.

- Which corals are used? -

Restoration projects greatly favor fast-growing branching corals.

The delicate branches of these corals are more susceptible to becoming fragments of opportunity and are also easier to microfragment than massive or encrusting corals.

Their fast-growing nature provides faster results for restoration projects, although focusing on just one type of coral can reduce the diversity of the ecosystem.

- Does it work? -

Coral restoration projects record survival rates of around 60 to 70%, according to a study published in 2020.

However around half of the projects in the study failed to adequately measure whether they achieved the goals stated at the start, including reef function.

Monitoring was also often brief, with an average of just one year, much less than the time needed for a reef to form, according to the authors.

Even so, the projects can produce real benefits.

A 2024 study of artificial reefs in Indonesia found that within four years, the structures had a coral carbonate budget - a measure of the reef's well-being - that was almost equal to that of a healthy natural reef nearby.

- What are the other considerations? -

Some experts worry that coral restoration is too often presented as a panacea for reef revitalization and point out that transplants will only survive if the environmental conditions are right.

This means addressing climate change first, which causes the warm temperatures that lead to coral bleaching.

"Well-designed and managed restoration projects have an important role to play, but there is only so much they can do if radical action on climate is not taken almost immediately," warned Lisa Bostrom-Einarsson, a marine ecologist who led the 2020 study.

In addition, other stress factors, from blast fishing to sedimentation, also need to be tackled if reefs are to have a future.

Reef restoration also rarely offers a replacement for destroyed ecosystems.

The Indonesian reefs examined in the 2024 study are still largely composed of transplanted corals, with few signs that "natural recruits" are taking root and building reef diversity.

Reef-building through microfragmentation also limits genetic diversity and could put reefs at risk if disease takes hold.

Even so, restoration done well offers considerable benefits, including coastal protection and increased marine life.

It also helps local communities that depend on fishing or tourism.

"Restoration won't save corals at the current rate at which we're losing them," said Gavin Miller, a marine scientist at the Global Reef Organization in Thailand.

"It's more about those localized impacts, the scale, and the awareness that you can raise from that."

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