Coral reefs are among the most climate-sensitive ecosystems and their survival is critical for marine biodiversity. Coral bleaching has been observed and reported worldwide, most notably in the Great Barrier Reef in Australia.

Consequently, restoration efforts are being applied worldwide to save our oceans, in line with the UN Decade on Ecosystem Restoration (2021-2030). In the Mediterranean, thanks to restoration efforts of the Medes Islands project, vibrant red coral colonies are making an unexpected comeback.

The threat to this unique ocean ecosystem not only stems from climate change associated with rising ocean temperatures, acidification, and extreme weather but also from human activities like poaching, coastal pollution, and overfishing.

The red coral colonies transplanted a decade ago on the seabed of the Medes Islands have survived successfully. The colonies seized years ago from illegal fishing, are thriving after the restoration actions of the University of Barcelona, in collaboration with the Institute of Marine Sciences (ICM — CSIC), to transplant seized corals and mitigate the impact of poaching.

“The restored community, that is the set of organisms in the environment where the transplanted coral is found, has been completely transformed in just ten years,” says Cristina Linares, professor at the UB’s Department of Evolutionary Biology, Ecology, and Environmental Sciences.

These findings indicate that replanting corals seized from poachers is effective not only in the short term, the first results were published after four years, but also in the long term, i.e. ten years after they have been initiated.

The success of coral restoration in the Mediterranean is not an isolated case. Across the globe, scientists are racing to revive dying reefs, including in the Western Indian Ocean (WIO), home to 16% of the world’s coral reefs. The region is now thought to host the second hotspot of coral reef biodiversity globally. These reefs support fisheries, and tourism, providing livelihoods to local communities in countries like Kenya, Tanzania, and Seychelles.

Due to the threats to the WIO coral reefs, associated with climate change and human activities, the International Union for Conservation of Nature (IUCN) has classified WIO coral reefs as “Vulnerable”.

In July 2024, the Western Indian Ocean Coral Reef Restoration Network was established, uniting local fishing communities to lead coral restoration efforts across the region. The restoration initiative is key to saving the endangered ecosystem.

According to Cristina Linares, the replanted community in the Medes project has assimilated the structure expected in natural red coral communities.

“This reinforces the key value of habitat-generating species such as red coral and the benefits that can grow from targeting them for conservation and restoration actions,” he says.

Corals seized from poachers require careful preparation and nurturing in controlled environments to ensure survival. The corals are then transplanted into protected marine areas where they can regenerate. However, finding suitable locations ensures long-term survival, and preventing further illegal poaching is a challenge to conservationists.

The IPCC (Intergovernmental Panel on Climate Change) warns that over 90% of the world’s coral reefs could disappear by 2050 if global temperatures continue to rise at current rates. Moreover, The Western Indian Ocean has lost approximately 20% of its coral cover in the last two decades due to climate stressors.

Despite the loss, restoration is being ramped up. For instance, the Kenya Wildlife Service (KWS) and local conservationists have experimented with coral transplantation to restore degraded reef areas in Kisite-Mpunguti Marine Park. Some transplanted corals have shown resilience to bleaching, with fish populations increasing in restored areas.

Similar projects are being done in Tanzania at the Chumbe Island Coral Park which has recorded over 80% survival rate of transplanted corals, and in Seychelles where over 50,000 corals have been successfully transplanted in a project led by Nature Seychelles.

Dr. Nyawira Muthiga, coral reef scientist at Wildlife Conservation Society (WCS) Kenya says,
“We have seen encouraging results from coral gardening and transplantation projects in Kenya and Tanzania. These interventions not only restore marine biodiversity but also support local communities that depend on healthy reefs for their livelihoods.”

To mitigate the effects of climate change on coral reefs, some marine scientists propose deep-water coral transplantation (30m+) as a strategy to help corals escape rising sea temperatures and bleaching events. Shallow-water corals (0-20m) are more exposed to marine heatwaves, UV radiation, and pollution, increasing bleaching risks.

Dr. Joaquim Garrabou (ICM-CSIC, Spain) says, “Transplanting corals to deeper, more stable environments could be an effective long-term strategy to buffer against climate-driven mortality.”

According to Dr. Nyawira, some coral species naturally occur at depths of 30-50m. Using these as donor colonies for transplantation could improve survival rates under climate change stress. Some research groups have tested deep-reef refuges, in the Great Barrier Reef, Australia as a strategy to protect coral biodiversity from extreme warming events.

However, deep-sea coral transplantation may prove challenging due to technical difficulties, and requires specialized diving equipment and techniques, making large-scale efforts costly. While cooler temperatures may reduce bleaching risks, lower light levels could disrupt coral-algae symbiosis, which is crucial for coral survival. Moreover, scientists are still studying whether transplanted corals at depth will grow and reproduce as successfully as they do in their natural shallow habitats.

“For restoration to be efficient, the source of stress that has degraded the system to be restored must be removed. In the case of the marine environment, due to global change, there is practically no corner of the world that is protected from human impacts. Therefore, before restoring, we must consider how to protect the sea effectively,” note the researchers.