Coral reefs are among the most dynamic and diverse ecosystems on the planet. They provide a safe habitat for hundreds of marine species, along with numerous resources necessary for the economic survival of smaller nations. Nevertheless, ocean acidification is one of the greatest threats that coral reefs face nowadays. It is now necessary to understand the problem, and to act quickly to limit the consequences potentially insuperable if coral reefs were to disappear.
How does a coral reef form?
Coral reefs are natural structures essentially built by hard coral colonies. Each coral is an invertebrate animal constituted of polyps. A polyp is an organism made of a mouth, stomach, wall and tentacles used for feeding and defense. Most of the corals are made of hundreds of those polyps, each genetically identical. Each polyp secrete its own exoskeleton made of calcium carbonate. Thus, hard coral species build reefs with the slow accumulation of these calcareous skeletons. Corals are furthermore considered as one of the biggest natural well of carbon on our planet.
The above video shows detailed and close-up shots of coral polyps feeding.
Why are coral reefs important?
Coral reefs have among the richest biodiversity on the planet, and provide ecological niches to numerous animals that find protection and food within the reef. According to the National Oceanic Atmospheric Administration (NOAA), more than 25% of the world’s marine biodiversity is found around coral reefs, as well as over 4,000 different species of fish.
Corals are also a necessity for many coastal countries. Coral reefs offer a natural barrier against erosion and flooding following strong weather events (hurricanes or typhoons, for example). Furthermore, coral reefs are of an invaluable economical importance, and supply essential goods and services such as food, raw material, water filtration, and tourism. Over 30 million people depend exclusively on those reefs for their subsistence and housing, particularly the populations living on coral islands or atolls (Wilkinson 2008).
It is difficult to calculate the exact monetary value of such an ecosystem, but according to estimations from experts at Diversitas in 2009, the goods and services supplied by coral refs have an average annual value of about $172 billion.
How are coral reefs threatened?
Corals are very sensitive animals, and do not tolerate big changes in their environmental conditions. They now have faced for multiple years various threats, such as overfishing, pollution, bottom trawling, warming sea surface temperatures, or ocean acidification.
It is possible that by the middle of the century, corals become incapable of surviving in numerous regions of the world due to ocean acidification, and that their dissolution will be faster than their rebuilding (Guinotte and Fabry 2008). As Lemonsea explained in the first article on this topic, the more acidity increases, the more energy is required to form a skeleton, and corals thus become more vulnerable.
In 2008, Clive Wilkinson explained that the world had already lost over 20% of coral reefs. In 2011, a report from the World Resources Institute indicated that 75% of coral reefs were at risk of entirely disappearing. In July 2015, a team of international scientists lead by Dr. Jean-Pierre Gattuso of the Laboratoire d’Océanographie de Villefranche published a worrying study on the future of our oceans. If we continue with the ‘business as usual’ approach and if the CO2 emissions increase at the same rate, we can expect irreversible consequences on the marine ecosystems.
Without corals, the marine biodiversity will sharply decrease, as it will equal a huge loss of habitat, food and protection for many species. Moreover, the sectors of tourism and fisheries in numerous local and national economies will highly suffer from the disappearance of coral reefs. Finally, coastal regions will inevitably face increased beach erosion, floods, and damages in towns located close to the oceans.
What can we do?
All hope is not lost yet. A team of scientist has already shown that some corals are capable of regulating their own pH levels internally (McCulloch et al. 2012). Moreover, scientists in many countries, like Ken Nedimyer in Florida, have successfully established coral nurseries to grow endangered coral species (see photo), and to insure the presence of numerous and different genotypes within the reef. These corals are then transplanted onto older reef sites, previously destroyed by storms, diseases or bleaching events, so the reef can rebuild. Additionally, scientific research on corals and their resistance to such events continues across the world.
In France, l’Initiative française pour les récifs coralliens (IFRECOR), dependent on the Ministère de l’Ecologie, has been committed since 1999 to ensure the protection and sustainable management of coral reefs in French waters.
Everything in our environment is connected, and it is therefore possible to help coral reefs indirectly in our daily life. Don’t hesitate to check out the Lemonsea article on 5 things you can do to fight ocean acidification.
This article was originally published in French on the blog Ocean pour le Climat for Le Monde: Les impacts de l’acidification des océans sur les récifs coralliens.