New project aims to revive corals – interacting with mangroves

The ‘jungle of the sea’ – this poetic metaphor describes the coral reefs, the most species-rich marine habitats. These reefs are the largest man-made structures on Earth and play a key role in the coastal ecosystems for which they serve as breakwaters.

But coral reefs, which are teeming with marine life – they are home to about a quarter of the life in the oceans, despite covering just 0.2 percent of the seabed – are under serious threat. Rising sea temperatures and acidification of the sea water are causing problems. The mostly small creatures that build the enormous reefs are helplessly exposed to these threatening changes because they are confined to their places.

According to calculations by scientists from the Intergovernmental Panel on Climate Change (IPCC) in 2018, if global warming reaches 1.5 degrees Celsius in 2050, 70 to 90 percent of the world’s corals will die. If the global temperature rises by 2 degrees, that would be 99 percent. Since the beginning of the industrial age, the Earth has warmed by about 1.2 degrees and is now heading for a warming of 2.7 degrees because too much CO₂ is still being released into the atmosphere. And more than 90 percent of the heat generated by anthropogenic greenhouse gases is stored in the oceans. Many corals are already dead because the average surface temperature of the oceans is currently at record levels.

In addition to rising temperatures, ocean acidification also causes problems for corals. This is related to the emission of CO₂ into the atmosphere: the oceans absorb about a third of the greenhouse gases that also enter the atmosphere. This lowers their pH value – from the current 8.1 to 7.8. When the pH drops below 7.7, coral reefs stop growing. In zones with elevated CO₂ levels, there are also vastly fewer young corals.

When corals die – the phenomenon is called ‘coral bleaching’ – the often very colorful coral groves fade. The reason for the loss of color is that the corals shed the differently colored microalgae, which live in symbiosis with them, when the water temperatures are too high. The corals then stop growing; They are also less able to defend themselves against enemies and competitors.

Coral bleaching is reversible when the algae return due to falling temperatures, but only within a certain period of time, about eight weeks. If this is not done, the coral will no longer be able to recover and will die completely. The dead, white limestone skeleton remains. If bleaching events become increasingly rapid, as they have been recently, reef systems will no longer be able to fully regenerate.

The death of corals is not just an ecological disaster: millions of people depend on it indirectly – be it because fish and other marine animals living in and on the reefs serve as their staple food, or because the reefs attract tourists. In a 2020 report, the Global Coral Reef Monitoring Network (GCRMN) estimated the value of goods and services related to coral reefs at US$2.7 trillion (over R2.2 trillion) per year.

However, under certain conditions, corals can regenerate after bleaching, although recovery in fast-growing coral species takes approximately ten to fifteen years, provided no further bleaching occurs during this phase. However, old reefs take decades to repopulate.

The Swiss start-up rrreefs has set itself the goal of rebuilding damaged coral reefs. The non-profit organization wants to restore the corals’ habitat with materials that are not directly affected by the acidic seawater. The artificial reefs, which consist of a modular system of environmentally friendly clay tiles, are an immediate measure, but in the longer term can form the core for new natural coral structures.

Together with the Mama Earth Foundation – a foundation founded in the Philippines that works on coastal reforestation projects – and Team Malizia – an offshore sailing team led by Boris Herrmann that is also committed to combating climate change – rrrefs launched a project to protect coral reefs to restore mangroves in the Philippines.

The long-term venture, which is supported by Zurich Group Germany, aims to restore damaged marine ecosystems in Pujada Bay on the Philippine island of Mindanao. The Philippine archipelago is home to nearly ten percent of the world’s coral reefs, but almost the entire population (98%) is considered endangered. About 70 percent of reefs are at high or very high risk.

Mangrove populations are also at risk: about a third of them have been destroyed worldwide in the past forty years. Mangroves are a plant community that includes approximately 70 different tree and shrub species worldwide. These evergreen plants are characterized by their striking roots, which rise like poles from the water and can find support even on soft, muddy ground. Mangroves also survive in salt water, so they are found on sea coasts and brackish estuaries.

Mangrove forests are one of the most biodiverse ecosystems on Earth; Their extensive root network provides countless animal species with protection and shelter from the open sea and contributes to water filtration and thus to the improvement of water quality. Like coral reefs, they contribute to coastal protection because they can absorb the force of storm surges. Moreover, mangrove forests are excellent CO₂ sinks; they bind significant amounts of greenhouse gases.

The project by rrrefs and its partners now combines the restoration of these two important coastal ecosystems – the coral reefs and the mangrove forests – in Pujada Bay, which was declared a Marine Protected Area in 1994. In this region, Team Malizia and Mama Earth Foundation have been actively involved in the restoration of the mangrove ecosystem for years through the construction of the Malizia Mangrove Park. In collaboration with the local university, they have already planted more than 800,000 mangrove seedlings. This also serves the purpose of providing local communities with a better income.

Restoring mangroves and coral reefs together offers benefits to both ecosystems, as rrrefs notes in a press release: the increased biodiversity of the reefs can help the young mangroves store more CO₂, and the mangroves can in turn help the regenerated reef by improve water temperature. and reduce sediment in the water.

To better understand the potential benefits of jointly restoring the two ecosystems, a control experiment is conducted: while approximately 3,000 mangroves are planted for two damaged coral reefs, only one of the reefs is rebuilt by rrreefs. This makes it possible to experimentally demonstrate whether joint repair offers benefits.

rrreefs will use its modular system of 3D printed clay tiles to regenerate the coral reef. They offer the advantage that any surface structure, flow properties and voids can be formed, which increases the chance that coral polyps can adhere to them. All kinds of reef creatures can also find shelter in the cavities. The modules therefore enable the restoration of a healthy reef ecosystem without further maintenance.

Scientists from Davao Oriental State University in Mati, who are involved in all steps of the project, will investigate whether the restored reef contributes to greater biodiversity in the mangroves and improves their CO₂ storage. The communities along the coasts will also be involved in the project because, as rrreefs states in the press release, their participation is crucial for the success and long-term sustainability of the restoration measures.

Marine biologist Ulrike Pfreund, scientific expert in the rrreefs team, says: “It is a complex experiment. If it works, the findings will be very valuable for future climate protection measures at sea.” The project is scheduled to be completed in February 2024.