It may come as a surprise to many people that we do not have an accurate list of the organisms that live in our oceans. To date, about 300,000 marine species have been described from around the world. Scientists have different views on what the total number, including as yet undiscovered organisms, may be. Some believe that there are only about 800,000, while others predict several million or more.
The inconsistency is in part due to the methods of extrapolating discovery rates from newly explored habitats to broader oceanic areas. Overall, our sampling of deep-sea environments has been very sketchy and when new habitats are first explored it is expected that new species will be discovered.
However, some parts of the world's oceans have been intensively studied, and the discovery rate of new species in those areas is lower. For example, the marine waters of Britain and Ireland have been well studied since the 18 th century. Of the 331 species of fish in the region listed by 1992, only 17 were described after 1900. However, among the smaller forms of life, new discoveries continue even in these relatively well-studied environments. Those have included the exciting discovery of two new phyla (major groupings of species) of small marine organisms in recent decades. The discovery of phyla is truly extraordinary as the 1.5 million or so species described on the planet can all be classified into only about 43 phyla. In 1983, the Danish zoologist, R. M. Kristensen discovered the phylum Loricifera living in the tiny spaces between marine gravel in sediments off the French coast. Since then at least 10 more species have been described (with rumours of 100s under investigation!), including inhabitants of coastal areas of North America . And in 1995 in the Kattegat between Denmark and Sweden , another new phylum (Cycliophora) was discovered living on the mouth bristles of the Norwegian lobster and feeding on scraps of the lobster's food.
This is not to say that only the smaller forms of life have remained a mystery. As recently as 1991 a new species of beaked whale ( Mesoplodon peruvianus ) was described from Peru and it is likely that yet others remain to be found. The most famous example of a new discovery is the coelacanth ( Latimeria chalumnae ), often referred to as the “living fossil”. The coelacanth lineage was thought to have been extinct for 80 million years when a live specimen was brought ashore by a fisherman off the eastern coast of South Africa in 1938. Miraculously this specimen made it into the hands of people who could recognize it and alert the scientific community. Efforts to discover where the fish came from eventually identified a small population living off the Comoros Islands between Mozambique on the African continent and Madagascar , where it had been caught with enough frequency for it to have been given a name in the native language. Just recently a second population was discovered from North Sulawesi . This second find has since been described as a new species, Latimeria menadoensis , using genetic evidence. In 2000, a third population (perhaps another species?) was verified in the St. Lucia Marine Protected Area on the northeast coast of South Africa . The total number of coelacanths may be greater than 100,000. Clearly there remains much to learn about life in the oceans.
Kenchington, E. 2002. The Effects of Fishing on Species and Genetic Diversity, The Reykjavik Conference on Responsible Fisheries in the Marine Ecosystem, October 1-4, Reykjavik , Iceland . In: M. Sinclair and G. Valdimarson (eds.). Responsible fisheries in the marine ecosystem. CAB International.