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Saving coral reefs: an ecological and economic priority

According to the latest IPCC report, 99% of coral reefs and the very rich ecological systems associated with them could die if Earth warms by 2°C by 2100. Besides their aesthetic, cultural, and touristic value, coral reefs render numerous ecosystem services. About 500 million people in the world depend on coral reefs to feed themselves, earn income (tourism) and preserve their coastal areas.

Coral reefs render precious services

The initial results of a study performed by the CRIOBE laboratory on the impact of climate change on the coral reefs of French Polynesia and published in mid-October, underlines two major impacts of their disappearance:

  • By no longer fulfilling their role as natural barriers, corals will offer less protection for coasts from large ocean waves and erosion. Indeed, they can absorb up to 97% of the energy of a wave. Simulations performed at Tahiti showed that “by 2100, if we are able to keep corals alive along with their structural complexity, reefs will continue to maintain their current capacity to absorb waves. This will be possible even if there is no decrease in greenhouse gas emissions and seal levels rise by 8 meter” emphasised the ecologist Valério Parravicini, who headed the study.
  • Their disappearance will also lead to a considerable loss of edible biomass. DNA analyses that will be carried out on more than 200 species of fish in the framework of this research project might allow identifying the species that feed directly and indirectly on the coral, and whose number is certainly underestimated today.

It’s not too late to reverse the trend

The good news is that the trend can be reversed, thanks to the formidable resilience of coral reefs. Attacked by a starfish that feeds on coral in 2006, then by the passage of a hurricane and episodes of bleaching linked to climate change, the rate of recovery of corals living on the reefs of Moorea in Polynesia fell to 0% in 2010. It is now more than 40% today. In order to re-establish and maintain these ecosystems, it is nonetheless important to limit climate change, which leads to the acidification and warming of the oceans, and to pollution.

According to the CNRS, the proportion of areas of the high seas depleted of oxygen (called dead zones) has increased more than fourfold over the last fifty years. Sites with low oxygen contents located close to shores, including estuaries and seas, have increased tenfold since 1950. When the level of oxygen is too low, marine life can no longer sustain itself. But surprisingly, nearly half of Earth’s oxygen comes from the oceans.

What can we do?

We cannot depend only on global action to combat global warming. Local and rapid actions can be performed on coasts, declares Serge Planes, a researcher with the CNRS and scientific director of the Tara Pacific expedition which explored 32 reef sites. These actions include stopping discharges of wastewater into the lagoon, working on watershed problems and deforestation, which lead to considerable deposits of silt on coral reefs and which smother coral, reduce pollution by prohibiting the use of suntan lotion, for example, reduce the number of tourists and, finally, regulate fishing on the coral reefs.

In the sea, the solution may come from a strange robot that will be sent to the Great Barrier Reef of Australia. Called LarvalBot, its mission will be to repopulate damaged reefs. The operation consists in sowing coral larvae, collected at the egg stage and then raised in nets, during the propitious breeding period, above the reefs. This experiment to save coral is being carried out by two Australian researchers, winners of a prize awarded by the Great Barrier Reef Foundation.

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