PREDICTIONS OF THE RESPONSE OF REEF CORAL COMMUNITIES TO CLIMATE CHANGE: EVIDENCE FROM THE PLEISTOCENE FOSSIL RECORD

The Western Australian coastline is a natural laboratory with which to assess the effect of climate change on reef coral communities. Coral communities composing Pleistocene (MIS 5e) reef assemblages exposed at five distinct localities were censused and the results compared to coral occurrence data published for the modern reefs offshore of each locality. The resulting comparative data set comprises modern and Pleistocene reef coral communities occurring over approximately 12^o of latitude and includes the zone of overlap between the Dampierian and Flindersian Provinces.

Modern reef coral communities show a pronounced gradient in coral composition over the latitudinal range encompassed by the study. Pleistocene reefs also are significantly correlated with latitude, although the correlation is not as strong. While dissimilarity amongst modern reef assemblages is correlated with distance, no such correlation was found for the fossil reefs. Migrations of coral taxa apparently are responsible for the pattern observed: a stronger Leeuwin Current during Pleistocene time produced a southward shift in the Dampierian-Flindersian boundary and enabled warm water coral assemblages to flourish up to 500 km south of their present range. The result of coral migration was to effectively homogenize the Pleistocene coral assemblages relative to their modern counterparts along the latitudinal range of the study. Hence coral diversity along the environmental gradient was lower in Pleistocene time than it is today. Since biodiversity and ecologic stability are related, these results emphasize the importance of mitigating human-induced diversity loss in present reef coral systems.