Coral reefs that survive rapid bleaching fuelled by global warming remain deeply damaged, with little prospect of full recovery, researchers said on Wednesday. Sixteen years after the 1998 El Nino ravaged coral in the Indian Ocean's Seychelles archipelago, no reefs had recovered their original growth rates and barely a third were expanding at all, they reported in a study, the first to track coral health over a two-decade period.
As important, perhaps, were qualitative changes. A dozen of 21 reefs tracked from 1994 were still struggling in 2014 against leafy algae, sea urchins and parrot fish to restore their original balance of shallow-water flora and fauna.
The rest underwent what marine biologists call a "regime shift", and are today composed of a new - and far less diverse - mix of corals.
"At any given site, there were at least 35 types of coral" in 1994, said lead author Fraser Januchowski-Hartley, a researcher from the University of Exeter. "Today, we see five to 10."
Four of the reefs only had two percent coral cover in 2014, and are likely to die out entirely.