Coral reefs can recover from severe bleaching events, says a study which looked at reefs in the Indian ocean.

The team monitored 21 reefs in the Seychelles since 1994, taking measurements of total number of plant-eating fish and nutrients reaching the reefs. Twelve out of 21 reefs were able to recover after severe bleaching in 1998.

The remaining became seaweed-covered ruins, writes Scientific American.

Cutting down on the amount of pollution can boost the resiliency of shallow reefs. "Reducing local impacts as much as possible will give them the best chance of survival," says Nicholas Graham from James Cook University and lead author of the study. "Managing the impacts to reefs is really about understanding and managing human actions."

The study has been published in Nature.

The researchers used many factors that influence reef health ranging from water depth, the complexity of its shape, nutrient levels to amount of grazing by fish and survival rates for young coral.

Studying growth in deep waters and looking at the complex, branching shapes atop the reef helped predict which reefs would or would not recover.

It was seen that reefs that have survived one bleaching event tend to become more resistant to future events. Complex reefs in deeper water recover best due to lower pollution, says the new study.

Acidification of the oceans from accumulation of carbon dioxide adds further stress to the reefs already burdened by pollution.

Under accumulated concentration of CO2, corals will dissolve instead of accumulating calcium carbonate. The high levels of the gas reduces photosynthetic efficiency and growth in most species.

Australia's Great Barrier Reef which contains the world's largest collection of coral reefs with 400 types of coral, 1,500 species of fish and 4,000 mollusc varieties has lost half its coral cover in the past three decades due to excessive bleaching and cyclones arising from climatic conditions.

Unesco had voiced concern about planned coastal developments, including development of coal ports and liquefied natural gas facilities that could further damage the world heritage site.