Coral Reefs: Fragile Giants

© Maggy Nugues/CRIOBE

A few weeks before the kickoff of the Tara Pacific expedition, scientific teams are more than ever ready to study the Pacific Ocean coral reefs and the dangers confronting them. For several decades, coral around the world has been facing more and more threats.

Like any link in an ecosystem, coral regularly faces natural threats, including diseases like “white band disease” (which in the 1980s decimated Caribbean reefs), and also ever-present predators. Acanthaster planci for example, a starfish that devours polyps, tends to proliferate in certain years, wreaking havoc on coral reefs. But these natural disturbances do not explain the dramatic collapse of coral populations.

Since the beginning of the industrial age, about 20% of reefs have disappeared forever. And the phenomenon doesn’t seem to be slowing down: 25% are in danger in the short term, and an additional 25% may be threatened by 2050 — a massacre that can be attributed to mankind.  Coral located near the coast in proximity with human activities suffers dramatically from population growth and  ensuing adverse consequences: pollution, destructive fishing practices, destruction due to mass tourism, dumping of sediment, etc.

Lauric Thiault

These threats are all the more worrisome because coral tends to be increasingly sensitive to these disturbances, weakened by climate change. Indeed, a significant temperature increase of surface water causes the death of zooxanthellae, the symbiotic algae in corals. Without algae, the polyp loses all its pigments and by transparence its limestone skeleton shows through. This is called “coral bleaching”. If conditions do not return to normal, the entire reef is threatened with death.

Finally, another menace is of human origin: ocean acidification. Massive release of CO2 in the atmosphere causes an increase in the acidity of water, disrupting the calcification process   necessary for creating the polyps’ external skeleton.  However, the magnitude of the phenomenon and its precise impact on the world’s reefs are still uncertain. It is imperative today to achieve a better understanding of the various threats confronting coral, in the hope of finding sustainable solutions that will ensure preservation of these teeming ecosystems. Given the urgency of the situation, the work soon to be accomplished aboard Tara will have great significance.

Yann Chavance


Other articles :

- Young reporters

- Animal, mineral or vegetal ? Corals at a crossroads.

- Departure of the Tara PACIFIC 2016-2018 expedition