Distribution of zooxanthella major clades across the Indian Ocean. Black sectors represent clade C, white sectors clade D.

Zooxanthellae are symbiotic dinoflagellate algae associated with many marine invertebrates, and are particularly important in cnidarians such as corals and zoanthids. Loss of algae ("bleaching") leads ultimately to the death of corals, a problem which has been dramatically increasing in scale in recent years.

Zoanthids obtain their zooxanthellae from the environment after settlement, so algal type to some extent depends upon regional availability. Since Palythoa hosts two types of zooxanthellae in the eastern Indian Ocean, but only one type in the west (see figure), this may reflect restricted availability of the second type.

Theory suggests biodiversity and ecosystem stability are linked, with more diverse systems better able to respond and adapt to environmental change. Restricted zooxanthella diversity in the western Indian ocean might mean coral communities in the region are more vulnerable to bleaching and other suggested consequences of global climate change.

Future studies will provide higher resolution data (including DNA sequences) at finer geographic scales, and investigate the ecophysiology of novel zooxanthella types detected.