Zooxanthellae

Abstract

The endosymbiosis between scleractinian (stony) corals and zooxanthellae (typically symbiotic dinoflagellates in the genus Symbiodinium) underpins the success of modern coral reefs. Reef corals (and other contemporary reefbuilders) gain a twofold advantage by hosting zooxanthellae. First, they can function as autotrophs and use the photosynthates thus obtained as an energy substrate. Second, for reasons which remain unclear, they are able to calcify much faster than their azooxanthellate counterparts (Cohen and McConnaughey, 2003). Together these phenomena explain why coral reefs have become dominant ecosystems in shallow, oligotrophic tropical seas. They also explain why coral reef bleaching (the loss of zooxanthellae from reef-builders) as a result of environmental stress is a major threat to coral reef ecosystems, particularly as a result of climate change-related seawater warming. The potential role of zooxanthellae in mediating the response of reef builders to ocean acidification also illustrates their importance as a contemporary subject of research.