Ocean roll-call: Marine species count yields surprising results


A global effort to catalog Earth’s marine biodiversity has shown that most species in the world’s oceans and seas will be fully classified by the end of the century, in part because the total number is lower than previously thought.

But the good news for marine biologists is that plenty still await discovery.

Marc Rius, UC Davis’s Marie Curie Postdoctoral Fellow in the Department of Evolution and Ecology, says that while the new estimate of all marine species is now 700,000 to about 1 million, only 226,000 have been identified.

Rius was a contributor on the project, which was coordinated by the Intergovernmental Oceanographic Commission of UNESCO. It drew information from the online database the World Register of Marine Species (WoRMS), with results published in the December 4, 2012, issue of the journal Current Biology.

“This project was an extremely exciting research endeavor for me,” Rius says of the paper. “We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered.”

The investigators believe that about 5,000 fish remain unknown today, in addition to a handful of cetacean and reptile species. The overwhelming bulk of the unknowns are invertebrates—crustaceans, mollusks, worms and sponges.

Of those yet to be discovered, 65,000 have already been collected and are stored in museums or universities, awaiting study and classification. Moreover, study results project that approximately one-third of species in more than 100 recent field studies around the world might be new to science.

The involvement of a large number of taxonomists allowed comparisons of organisms and interaction among experts from all different groups of marine taxa.

In addition, the project pulled researchers from countries around the world to ensure that the count included all oceans and seas. Rius himself was responsible for covering and integrating information from a region that it is poorly known—Africa, which includes both Atlantic and Indian ocean waters.

At the steady clip with which scientists are discovering species—20,000 were newly described and named in the last decade, a rate that is increasing—it is estimated that almost every eukaryotic marine species will be identified by the end of the century.

“This study highlights the importance of taxonomy in providing a holistic understanding of life in the oceans, which has implications for a broad range of disciplines including biogeography, ecology, evolution and conservation,” Rius adds.

“This is something extremely important as before starting any study, one needs to have a clear idea of how many species are being studied.”

Rius’ specialty is in the underlying mechanisms that determine and maintain species ranges, including how alterations such as human-caused disturbances and biological invasions affect the composition of native species and their ecosystems. He will be starting a faculty position late this year at the National Oceanography Centre, University of Southampton, UK.