Most people are fascinated by the colorful and exotic coral reefs, which form habitats with probably the largest biodiversity. But human civilisation is the top danger to these fragile ecosystems through climate change, oxygen depletion and ocean acidification. Industrialisation, deforestation and intensive farming in coastal areas are changing dramatically the conditions for life in the oceans. Now scientists at the Max Planck Institute for Marine Microbiology from Bremen together with their colleagues from Australia, Sultanate of Oman and Italy have investigated how and why the corals die when exposed to sedimentation. According to their findings, oxygen depletion, together with an acidification of the environment, creates a chain reaction that leads to coral death.
Reef forming stone corals inhabitat the light-flooded tropical shallow coastal regions 30 degree south and north of the equator. Coral polyps build the carbonate skeletons that form the extensive reefs over hundreds to thousands of years. Photosynthesis of the symbiotic algae inside the polyps produces oxygen and carbohydrates from carbon dioxide and water, thereby feeding the polyps.
Since the 1980s the process of coral bleaching is under study: elevated temperatures of 1 to 3 degrees induce the algae to produce toxins. The polyps react by expelling the algae and the coral reef loses its colour as if it was bleached. Without its symbionts the coral can survive only several weeks.