"It may not be mission impossible to describe all the marine species in the ocean," Appeltans said. "We are describing 2,000 new marine species every year. If we can keep that momentum, we can start knowing exactly what's living on our planet."
In previous attempts to guess numbers of ocean species, scientists often made extrapolations based on rates of previous discoveries or numbers of unknown species in sample collections. Those methods led to crude estimates that ranged from 300,000 to more than 10 million total species in the seas.
To come up with something more accurate, Appeltans worked with 120 of the world's leading experts on specific groups of marine organisms. Based on their intricate knowledge of taxonomy, the experts came up with educated guesses about numbers of known and unknown species in their own particular fields. The study also employed a statistical model to incorporate expert assessments with known information about changes in rates of discovery over time.
Overall, the study counted about 400,000 described species of marine species, though about 40 percent of those had been described multiple times and had been given more than one scientific name. That led to a corrected tally of about 226,000 known marine species, the team reports today in the journal Current Biology. The list includes about 200,000 animal species, 7,600 plants and more than 1,000 fungi.