REEF Services: understanding the impact of coral reefs

The coral reefs are home to the world’s greatest marine biodiversity and provide a host of services to humans: fishing, tourism, coastal protection. More than 500 million people rely on them for their subsistence. The problem is that these oases of life are extremely sensitive to changes in their environment (warming, acidification, pollution, overfishing) and we are now seeing the unfolding of a massive and worldwide coral bleaching event due to the disruption by high temperatures of the symbiosis between the coral and its microalgae. 

In 2016, 93% of the Great Barrier Reef suffered from bleaching and approximately 80% of the coral in Kiribati, Samoa, Fiji and Tonga is already dead. A new episode of bleaching began in March 2017. According to Valeriano Parravicini, professor and researcher at the École Pratique des Hautes Etudes in Perpignan, “this is the first time that two massive episodes of bleaching has occurred over two consecutive years”. While the physiological mechanisms behind this phenomenon are well known, little is known about what impact bleaching will have on the workings of the reefs and the services provided to humans. This research project, headed by Parravicini in collaboration with researchers from six French, British, US and Australian laboratories, sets out to take stock of the services provided by the fish of the reefs and estimate the long-term impact of bleaching.

Comprehensive assessment

“We wanted to study three types of services provided by the fish of the coral reefs”, explains Parravicini. These are the supply service, i.e. the edible species; the cultural service, based on the aesthetic and recreative value of certain species; and the support service, i.e. the ecosystem’s necessary processes, by studying plant-eating fish which prevent algae from colonising corals, or the species that contribute to the carbon cycle by ingesting carbonate.” The first step will be to assess the role of each coral fish species in providing these ecological services, and quantify the extent of their participation. Which species contribute the most, and to which service? Are there conflicts between these services?

Are there conflicts between these services? The second step will be to delve into existing databases from the many observation stations in the Pacific islands for data on these abundant species. “We’ve been lucky enough to have time series of over 30 years from the Pacific stations monitored by CRIOBE research centre and environmental observatory, the Moorea station in particular”, the researcher explains. Reviewing past data will reveal changes in the abundance of these species according to environmental parameters such as water temperature and habitat availability.

Mapping future risks

The final step will be to make future projections by mapping future risks, drawing on various warming scenarios and models that link temperature anomalies and the occurrence of bleaching episodes. Which species will be affected and to what extent? What will be the consequences for the three types of services under study? These data will provide precious insight for assessing the impact of global warming in an island environment, and more generally the impact on populations who live off the coral reefs. One thing we do know, is that when corals die, their services die with them. If nothing is done to offset the local and global threats to the reefs, they may very well diminish to the point of no being unable to support human populations by 2050, as stated by a report by the World Resource Institute.