image: This shows oral reefs in the Red Sea. view more
Credit: Xavier Turon
Every taxonomist has calculated the number of existing species within their specialty and estimated the number that remain to be discovered, both through statistical models as based on the experience of each expert. According to Enrique Macpherson, researcher at the Center for Advanced Studies of Blanes (CEAB-CSIC, Spain), who has participated in the study: "Bringing together the leading taxonomists around the world to pool their information has been the great merit of this research".
The statistical prediction is based on the rate of description for new species in recent decades. The results show that the total number of marine species would be about 540.000. However, this number ranges from 320.000 to 760.000.
Meanwhile, the experts have made another estimation based on their experience and on a projection of the number of species found in the sampled areas. According to this prediction, the number of species ranges from 704.000 to 972.000. According to Xabier Turon, who also works as a researcher at the Center for Advanced Studies of Blanes (CEAB-CSIC): "the calculations for both methods yield figures with the same order of magnitude, which confirms that we know about one third of the species".
All the information pooled by the experts show that just 230.00 species are correctly described. In fact, researchers found about 170.000 cases of synonymy among previously known species. That is, one single species described under two (or more) different names. Among the order, for instance, of cetaceans (Cetacea), researchers have found that there are 1.271 different names applied to just 87 species. CSIC researcher Damia Jaume, from the Mediterranean Institute for Advanced Studies (IMEDEA, CSIC-UIB) and also involved in the study, states: "the best known is the species, and its greater size and commercial interest, the most common is synonymy".
Of the roughly 230.00 marine species known, about 200.000 belong to the kingdom Animalia; 7.600 to Plantae; 19.500 to Chromista; 550 to Protista; and 1.050 to Fungi. The research has only counted with eukaryote organisms, i.e. those whose genetic information is enclosed in a cell nucleus, which has left out bacteria, viruses, and archaea.
What remains to be known
The research data suggest that there are still about two-thirds of marine species to be described, most of which would already be inventoried. Although most of the ocean has not been sampled, Macpherson states that "marine environments are less diverse and have very limiting factors such as light, which homogenizes the species that inhabit them. Thus, it is to be expected that the oceanic diversity is less than terrestrial diversity". Although there is no consensus yet on the number of species that inhabit the earth's surface, this figure could be about 10 higher than the aquatic biodiversity.
CSIC researcher thinks that "maybe in a century's time, all marine species have been able to be described. However, the most we know, the most we can assure the exact number of aquatic biodiversity".
The research was led by the Flanders Marine Institute (Belgium) and the University of Auckland (New Zealand), and they have coordinated the activity of other 144 institutions.
The information compiled by researchers is available in an open access log through the website http://www.marinespecies.org
Journal
Current Biology