Researchers in Australia and Sweden have found that coral bleaching and death can have a direct effect on how reef-dwelling fish learn about their environment - particularly how to avoid predators.

Killer starfish threaten Great Barrier Reef Crown-of-thorns starfish have a voracious appetite and waves of carnivorous starfish are eating their way through Australia's Great Barrier Reef - and sugar cane farming is being blamed. Researchers at Australia's Institute of Marine Science (AIMS), just outside Townsville, Queensland, in north-east Australia, have mapped the pattern of destruction. "Coral cover is half of what it was 27 years ago, coral cover is going down at an alarming rate." Dr Katharina Fabricius, coral reef ecologist and AIMS principal research scientist, told the BBC World Service programme Discovery. She said the biggest culprit was the Crown of Thorns Starfish (COTs). "There are three main sources for the coral decline, one is storms, however 42% is attributed to Crown of Thorns Starfish - and just 10% due to bleaching. This compares with 70% due to bleaching for reefs elsewhere in the world , such as in the Caribbean." “Crown of Thorns are very fecund animals - each female can produce between five and 20 million eggs ” John Brodie, James Cook University Bleaching occurs when corals are stressed by changes in conditions such as temperature, light, or nutrients. They expel the symbiotic algae living in their tissues, causing them to turn completely white. Australian scientists are now looking at ways to reduce the destruction wreaked by starfish, which have the ability to smother coral and digest the fleshy parts.

Corals are likely to suffer as a result of the changes to our oceans The health of the world’s oceans is deteriorating even faster than had previously been thought, a report says. A review from the International Programme on the State of the Ocean (IPSO), warns that the oceans are facing multiple threats. They are being heated by climate change, turned slowly less alkaline by absorbing CO2, and suffering from overfishing and pollution. The report warns that dead zones formed by fertiliser run-off are a problem. It says conditions are ripe for the sort of mass extinction event that has afflicted the oceans in the past. It says: “We have been taking the ocean for granted. It has been shielding us from the worst effects of accelerating climate change by absorbing excess CO2 from the atmosphere. “Whilst terrestrial temperature increases may be experiencing a pause, the ocean continues to warm regardless. For the most part, however, the public and policymakers are failing to recognise - or choosing to ignore - the severity of the situation.” It says the cocktail of threats facing the ocean is more powerful than the individual problems themselves. Coral reefs, for instance, are suffering from the higher temperatures and the effects of acidification whilst also being weakened by bad fishing practices, pollution, siltation and toxic algal blooms. IPSO, funded by charitable foundations, is publishing a set of five papers based on workshops in 2011 and 2012 in partnership with the International Union for Conservation of Nature (IUCN’s) World Commission on Protected Areas.

Various factors, from cyclones to the Crown of Thorns starfish, are being blamed for the loss of the reef.

Australia's Great Barrier Reef has lost more than half its coral cover in the past 27 years, a new study shows.