Up to two thirds of marine species still unknown to science

ca5bed13-4cf0-4054-a8dd-fb3fb2bf8211

Editor's Picks
Features Post
The brightest pupils
04 October 2021
Features Post
Dealing with egg ‘fungus’
04 October 2021
Features Post
Rathbun’s tetra in the wild
13 September 2021
Fishkeeping News Post
Report: 2021 BKKS National Koi Show results
13 September 2021
Features Post
The World's forgotten fishes
16 August 2021


At least one third of the species living in our oceans, and perhaps up to two thirds, are unknown to science according to the work of an international research group.

In a study published in Current Biology, the researchers calculate that there are less than one million marine species, far fewer than some previous estimates. Around 226,000 species have been described by science and as many as 72,000 more are in collections awaiting description.

The good news is that the rate of discovery is increasing, with an unprecedented 20,000 new marine species described in the last decade alone, suggesting that most marine species will be discovered this century.

"This is by far the most comprehensive assessment of how many marine species have been described to date, and how many undescribed species experts believe there may be," says Associate Professor Mark Costello from The University of Auckland who co-led the research with Ward Appeltans of Flanders Marine Institute and the Intergovernmental Oceanographic Commission (IOC) of UNESCO.

The study involved 120 of the world’s top experts on the taxonomy (classification) of marine species, and represents the sum of their opinions on how many species may exist. Many of the species yet to be discovered will come from amongst the smaller crustaceans, molluscs, algae, worms, and sponges.

"Knowing how many species there are in our oceans, and describing them, is vital for science and conservation for several reasons," says Dr Costello.

"Better understanding of what species exist enables more accurate estimates of extinction rates due to habitat loss. In addition, having a standardised master list of species names is essential for quality assurance in science and the management of natural resources.

"Inventories like these also reveal where taxonomic effort will discover most new species and this is the first step in biology, akin to an explorer discovering new land."

The near completion of the World Register of Marine Species (WoRMS) – an open-access, online database that has received contributions from almost 300 scientists from 32 countries – set the stage for the current research. Based on its success, the scientists are calling on other research communities to create similar international collaborations and share their data online.

The study supports previous research by Dr Costello and colleagues, which used statistical modelling and an earlier version of WoRMS to reach a similar estimate of the number of species on Earth and in the oceans. It is the culmination of 14 years’ work for Dr Costello, who began a European Register of Marine Species in 1997 that expanded until the World Register was initiated in 2006. He is currently Chair of the WoRMS Steering Committee.

Why not take out a subscription to Practical Fishkeeping magazine? See our latest subscription offer.