In what is undoubtedly the biggest and most comprehensive attempt undertaken to answer the age-old question about the number fishes in the sea, the Census of Marine Life (COML) has estimated that there are more than 230,000 species out there in the oceans.
The results of the 10-year study of the diversity, distribution and abundance of life in the world’s oceans were published on 2 August.
According to Patricia Miloslavich of Universidad Simon Bolivar, Venezuela, the co-senior scientist of the COML, the survey covered species “from coast to the open ocean, from the shallows to the deep, from little things like microbes to large things such as fish and whales.”
More than 360 scientists have, over the past decade, surveyed 25 regions and the results show that around a fifth of the world’s marine species are crustaceans such as crabs, lobsters, krill and barnacles. Along with molluscs (squid and octopus) and fish (including sharks) they make up about half the species in the seas.
The species that are most frequently seen in conservation campaigning whales, sea lions, turtles and sea birds make up less that 2 per cent of marine species.
The study has also highlighted areas that should be of concern for conservationists.
According to Mark Costello of the Leigh Marine Laboratory, University of Auckland, in every region it is the same store of a major collapse of what were once abundant fish stocks or crabs or crustaceans that are now down to barely 5 per cent – 10 per cent of what they used to be.
These are largely the result of over-harvesting and poor management of those fisheries and that is probably the biggest and consistent threat to marine biodiversity around the world, he added.
The main threats to marine life include over-fishing, degraded habitats, pollution and the arrival of invasive species. But there are other problems on the horizon, rising water temperatures and acidification due to climate change and the growth in areas of the ocean that being low in oxygen are unable to support life.
According to the COML, the most diverse regions are around Australia and Southeast Asia and Costello says the area is also a hotspot for terrestrial biodiversity, which has been known for about 100 years.
He adds that it appears that region with the coral reefs has always had a very high rate of speciation and has a very diverse range of habitats from the deepest areas of the oceans to large areas of shallow seas that can support coral reefs.
Australian and Japanese waters have more than 30,000 species each with the oceans off China, the Mediterranean Sea and the Gulf of Mexico next in line.
The COML is being co-ordinated in Washington DC by the Consortium for Ocean Leadership and involves scientists from 80 countries.
According to the team, by creating the first catalogue of the oceans of the world, we can start understanding the great ecological questions about loss of habitat, pollution, over-fishing and all the other problems created by man that are affecting the sea.
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