The future of coral reefs in the Anthropocene era is now threatened by the billions of tons of carbon dioxide emitted into the atmosphere. Ocean acidification (OA) is thus, after global warming, the other problem that coral reefs will have to face.


The overall objective of ACID REEFS is to better understand the response of coral reefs to ocean acidification through an integrated approach. ACID REEFS is lead by Dr. Laetitia Hédouin (CNRS) from the Center for Island Research and Environment Observatory in Moorea.

A glimpse on the results from ACID REEFS


A | Effects of ocean acidification on ACID REEF species

The ACID REEFS experiments performed in Mo’orea have shown that the sensitivity to OA is dependent on the coral species considered: Pocillopora verrucosa, one of the dominant species of the reef of Mo’orea, being relatively insensitive to the pH scenarios planned for the end of the century and more extreme, while other species of the genus Acropora and Montipora are more sensitive to extreme pH.

While the growth and / or calcification of adult corals is relatively unaffected by a drop in pH of 0.3 units, coral larvae change their swimming behavior and decrease their rate of metamorphosis. Combined with reduced growth of coralline algae, ACID-REEFS unveils the importance of studying other life stages and organisms to truly grasp and understand the effects of OA on the reef.

Most of the works performed on corals is done on adult stages, because it is relatively easy to work on coral fragments, but ACID REEFS shed light on the sensibility of coral life cycle to OA and pelagic life stages of corals, relatively unexplored required further attention, if we want to really protect the reefs.

While adult living corals have a certain capacity to resist the drops in pH predicted for the end of the century (-0.3 units), dead skeletons are more sensitive to decreasing pH and raises some questions on how the high mortalities experienced by reefs due to global warming could weaken the future resistance of coral reefs to OA.

Another aim of ACID REEFS was to set up a reef vulnerability assessment for Moorea using an ecological and social approach. This work revealed that the fringing reefs of the island of Moorea are more vulnerable than the reefs of the outer slope and the reefs which are vulnerable today will see their vulnerability increased by 2050 in the context of climate change. Some municipalities on the island of Moorea are already more vulnerable than others and we hope priority adaptation and / or mitigation measures will be put in place to preserve them.


B | The perception of ocean acidification / coral reef threats (a collaboration with Kahi Kai & the IRCAN)

OA is relatively unknown to civil society, or poorly understood, there is a real urgency to connect civil society to the threats facing the reefs and to make them aware of the consequences of the loss of the reefs. To increase the awareness of civil society to the effects of OA on reefs, numerous communication actions such as intervention in schools, workshop, training, working groups, teaching, supervision of trainees or round tables were carried out throughout the project. In order to determine whether those were effective means to sensitize the general public, the choice was made to assess the perception of OA by the civil society via an survey (online and during events/fairs).

The results from more than thousand respondants indicate that it is essential to target communications actions for people over 34 years of age living in metropolitan France. This survey further indicates that the communication of choice to promote awareness of the effects of OA on coral reefs is via the internet.

Increasing communication actions on OA is crucial to favor a sense of ownership, responsabilities and legacy into the future of coral reefs. In particular, for a shift from a civil society looking at the deterioration of its environment to an active civil society engaged in various actions to defend and actively protect coral reefs for the next generations.


C | Conclusions & Perspectives

The results from ACID REEFS provide a new vision of the effects of OA on Polynesian coral reefs. At the scientific level, new approaches on corals have been carried out (biological breaking point, behavior of coral larvae) revealing that the study alone of the response of adult corals to OA does not really reflect the consequences of OA on the reef. The different life stages of the coral life cycle must be taken into account in order to have a global and more realistic vision of the effects of OA on reef species. Thus, there is an urgent need to develop studies focusing on young life stages to ensure that the ecological resilience of reefs is preserved.

At the societal level, many communication actions were carried out in schools, with civil society via several approaches (conferences, workshops, cartoons), and a survey made it possible to better assess the perception of OA by general public. This survey is now opening avenues for improving communication on the effects of AO on reefs, focusing on most people over the age of 34, via the internet and proposing actions creating a link with the reef.

For public and private decision-making, the work carried out at the socioecosystem level provides conceptual diagrams and a framework for assessing the vulnerability of reefs, this new tool can be very interesting for managers and politicians to identify priority areas for action. ACID REEFS has assessed the vulnerability of socioecological systems in Moorea, these results will be presented and discussed with Polynesian authorities and we hope will serve as a basis for prioritizing certain key management actions to promote the resilience of reefs identified as vulnerable in Moorea.

Research consortium

ACID REEFS is led by Dr. Laetitia Hédouin and brings together a consortium of scientists from innovative and complementary disciplines from seven laboratories / research centers in four countries: CRIOBE – French Polynesia, IAEA – Monaco, CSM – Monaco, Rhode Island University -USA, University Gothenburg – Sweden.

Communication and outreach: Non-profit organization Kahi Kai (France, Hawaii, French Polynesia –

Funding: Fondation de France and  by the Ocean Acidification Program of the French Foundation for Research on Biodiversity (FRB – and the French Ministère de la transition écologique.