Overfishing, pollution, climate change and destruction of habitats like coral reefs are all putting marine life in trouble and academics fear the risk is not being taken as seriously as concerns for the loss of animals and plants which live on land.

By using the most comprehensive conservation data available for both marine and non-marine organisms, researchers show that 20 to 25 percent of the well-known species living in seas are now threatened with extinction - the same figure as land living plants and animals.

"Until now, there has been a general assumption that, despite pressures on marine environments like pollution and overfishing, marine species are unlikely to be threatened with extinction," said Thomas Webb from University of Sheffield's department of animal and plant sciences.

"We have shown that, on the face of it, there are indeed far fewer marine species of conservation concern; but much of this can be explained by the fact the conservation status of fewer marine species has been formally assessed," Webb said.

When the team concentrated on those animals and plants, where estimates of extinction risk were the most reliable, the difference between marine and non-marine species disappeared.

Instead, in these groups around one in every four or five species was estimated to be at a heightened risk of extinction, whether they live on land or in the sea.

The study is also part of efforts to better use the wealth of existing data on marine ecosystems to track past changes and to predict how they are likely to respond to future pressures.

The study appeared in the journal Current Biology.