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.
Human impact through fisheries, pollution, climate change and habitat destruction are all putting our seas in trouble but researchers fear the risk is not being taken as seriously as concerns for the loss of land living animals and plants.
Using the most comprehensive conservation data available for both marine and non-marine organisms, research from the University of Sheffield, has shown that 20 to 25 per cent of the well-known species living in our seas are now threatened with extinction -- the same figure as land living plants and animals.
This assessment was done by checking species against a list of criteria published by the International Union for the Conservation of Nature, a time-consuming process that has been completed for only three per cent of marine species, with no assessments at all in three quarters of the major groups of marine animals and plants.
As it turns out by concentrating on those groups of animals and plants which are best known, and where estimates of extinction risk are likely to be most reliable, the difference between marine and non-marine species disappears. Instead, one in every four or five species in these groups is estimated to be at a heightened risk of extinction, whether they live on land or in the sea.
The paucity of recorded marine extinctions does however suggest that the threat to marine species may not yet be sufficiently great to force many to extinction, in part because the geographic scale of human activities in the seas has increased markedly only in the last century. This buys time to implement conservation efforts before species are lost, yet the loss of marine populations is already common, and so the lack of recorded global extinctions is not cause for complacency. Rather, it should spur us on to trying to achieve a better understanding of the species that inhabit our oceans and the threats that they face, taking action to increase rates of taxonomic description and assessment of extinction risk in order to prevent a biodiversity crisis in the oceans as severe as that on land.
The research, which was funded by the Royal Society, forms part of a broader program of study challenging the traditional division between marine ecology and 'mainstream' ecology, the notion that marine systems are somehow fundamentally different from terrestrial systems, and that this demands separate research approaches and indeed research institutes - to study them.
This is not to say that there are no important differences, but rather that assumptions need to be tested in order to make sensible decisions about managing the marine environment.