"Worse than we thought"
"When Tamar Goulet of the University of Mississippi, scoured studies for data on 442 coral species, she found that 77 per cent host only one type of alga (Marine Ecology Progress Series, vol 321, p 1). She also found that in these species the type of alga does not change over time, or when they are exposed to disease or higher temperatures. 'If climate change continues, coral reefs may undergo a significant change in biodiversity,' says Goulet".There is a longer report here.
The eminent reef scientist Barbara Brown reported at ISRS2006 last week that there is some evidence that in some cases the host coral animal itself may be able to adapt more than thought - at least from evidence gathered in the Andaman sea.