At least one-third of the species that inhabit the world's oceans may remain completely unknown to science. That's despite the fact that more species have been described in the last decade than in any previous one, according to a report published online on November 15 in the Cell Press publication Current Biology that details the first comprehensive register of marine species of the world -- a massive collaborative undertaking by hundreds of experts around the globe.
The researchers estimate that the ocean may be home to as many as one million species in all -- likely not more. About 226,000 of those species have so far been described. There are another 65,000 species awaiting description in specimen collections.
"For the first time, we can provide a very detailed overview of species richness, partitioned among all major marine groups. It is the state of the art of what we know -- and perhaps do not know -- about life in the ocean," says Ward Appeltans of the Intergovernmental Oceanographic Commission (IOC) of UNESCO.
The findings provide a reference point for conservation efforts and estimates of extinction rates, the researchers say. They expect that the vast majority of unknown species -- composed disproportionately of smaller crustaceans, molluscs, worms, and sponges -- will be found this century.
Earlier estimates of ocean diversity had relied on expert polls based on extrapolations from past rates of species descriptions and other measures. Those estimates varied widely, suffering because there was no global catalog of marine species.