Effets des polluants sur les écosystèmes récifaux

Pollutant effects on coral reefs ecosystems. — During the last decade, it has proven more and more obvious that coral reefs have become the most threatened class of ecosystems of the world far before the tropical forests. Indeed, not only their global area is much lower but the coral reefs are affected by the largest array of degradation factors, especially toxic pollutants, strictly related to human impacts on the oceanic and global environment. A significant part of reef pollution results from the discharge into marine environment of a large range of pollutants : hazardous chemicals, oil offshore industry and piping of crude oil, lastly from atmospheric transfer of chemicals to the surface of the sea via precipitations. Subsequently will be found in reef waters and sediments a number of toxic metals, hydrocarbon, persistent organic pollutants (POPs), pesticides discharged from land by run off, especially herbicides, as well as antifouling paintings not to mention cyanides widely in unlawful use for reef fishing in developing countries. POPs have been detected in reef ecosystems everywhere they have been investigated. Even non-persistent pesticides are currently found in reef waters and sediments located next from coastal intensive tropical crops. Studies on ecotoxicological effects of reef pollutions have been carried out at various extents according to the class of chemical concerned. Though oil impact on reefs and even heavy metals pollution has been rather intensively investigated, at the opposite, pesticides and especially herbicides have given way to a much smaller number of researches. This fact is quite surprising as herbicides display an impressive potential impact on hermatypic scleractinians due to their extreme toxicity for Dinoflagellate symbiotic algae. Various studies have shown up that a number of toxic pollutants such as hydrocarbons, pesticides or cyanides prevent coral gametes fecundation and the settlement of planula as well as their further metamorphosis, impeding therefore the colonies renewal or the restoration of the ones already degraded subsequently to human activities. Other investigations demonstrated that reef bleaching could be generated by exposure to very low levels of herbicides as well as cyanides that trigger the loss of zooxanthellae. On the other hand, lower concentrations of herbicides, sometime in the order of one μg. L– 1 as diuron and various triazines, can inhibit photosynthesis. Additionally to their direct effects on hermatypic scleractinians, toxic pollutants discharged into the coral reefs environment can impinge on other reef habitats of the coral ecosystem, especially on the sea-grass beds growing in its lagoons. Lastly, the impact of various terrigenic pollutants, as herbicides, on other coastal ecosystems especially mangrove can indirectly act on coral reef communities with which they share some of their components, especially fishes and invertebrates : a number of reef species relying on mangrove habitat as nurseries for their larval and/or their juvenile instars.
Il est devenu de plus en plus évident au cours de la dernière décennie que les récifs coralliens représentent de loin le type d’écosystème le plus menacé de la planète, beaucoup plus que les forêts tropicales. En effet non seulement leur surface totale est beaucoup plus faible, mais à la différence de ces dernières, ils sont exposés à tous les types de dégradations d’origine anthropique en particulier au spectre complet des polluants toxiques. Une fraction significative des polluants des récifs proviennent de rejets en mer d’une large gamme de composés chimiques dangereux, de l’exploitation de gisements de pétrole offshore, et enfin du transfert de polluants atmosphériques dans les eaux marines via les précipitations. En conséquence, des métaux toxiques, des hydrocarbures, des polluants
Ramade François,Roche Hélène. Effets des polluants sur les écosystèmes récifaux. In: Revue d'Écologie (La Terre et La Vie), tome 61, n°1, 2006. pp. 3-33.