Sydney, June 17 (IANS) Beautiful coral reefs are increasingly under threat from climate change, and so are 4,000 species of fish, critically dependent on them for food, shelter or reproduction, warns a study. It blames global warming for the latest threat to marine biodiversity. Already many corals have died because of warmer waters associated with climate change.

“The problem for specialist coral fishes is that when the corals die, the fish have nowhere else to go. Other kinds of fish live more independently, but depend on reefs for shelter in the juvenile stage of their life,” said the study’s co-author Philip Munday.

“As coral communities become less healthy, so too do the fish communities. A loss of diversity in corals due to bleaching and other impacts is also likely to lead to a loss in diversity among the fishes which inhabit them,” the researchers said.

Like corals themselves, coral fishes seem to prefer a temperature-stable environment and heating of the water may affect them in unpredictable ways.

For instance, Munday said, warmer water may lead to higher survival rates in baby fish - but it could equally send a signal to adults to stop breeding, as reproduction is often governed by water conditions.

Recent research has shown that some species might grow more slowly if temperatures go above their preferred range.

An estimated 200 million people worldwide derive their livelihoods and a major source of sustenance from coral reefs. In Australia, a $5 billion tourism industry depends significantly on visitors being able to view corals and their colourful fish.

The problem stems in part from the fact that when many coral fish breed, their eggs are swept out to sea, and the baby fish then swim back and resettle on the reef.

If reefs have been damaged or the composition of their corals altered due to global warming impacts, this process of re-stocking the reefs with fish may be disrupted.

At the same time, the baby fish are likely to be affected by changes in water temperature and the acidification of the oceans.

As to simply heading deeper, into cooler water, Munday said that while coral reef fish do sometimes go deep, mostly they prefer the sunlit waters of the surface where the food supply is greatest, and tend to observe fairly strict depth boundaries.

The report appears in Fish and Fisheries, co-authored Munday, Geoff Jones, Morgan Pratchett and Ashley Williams of Centre of Excellence for Coral Reef Studies and James Cook University.