The Role of Zooxanthellae in Marine Invertebrates

The importance of zooxanthellae in marine environments cannot be understated. Their role as a source of nutritive energy to corals underpins the success of reef-building systems worldwide, forming some of the most productive ecosystems on earth. The diversity of these unicellular symbiotic algae, which belong to the genus Symbiodinium, is enormous. Multiple hosts, multiple types of algae and the diverse habitats in which these organisms are found suggests a diverse reservoir of symbiont types in almost every region. This review focuses on the functional and genetic diversity of Symbiodinium, the specificity and flexibility of the host-algal association, and the implications they present. Symbiodinium types vary in their physiological response to environmental changes, and the possibility that hosts may alter their populations of symbiotic algae in response to external change might suggest zooxanthellae influence the ecological resilience of host species. This then raises the question of whether or not these changes are sufficient for hosts to tolerate climate change and other negative impacts on aquatic ecosystems worldwide