SCIENCE

Ocean More Diverse than Expected, Census Finds

October 8, 2010

Ten years ago a group of marine scientists founded the Census of Marine Life and set out to answer three questions: What did live in the oceans? What does live in the oceans? What will live in the oceans? More than 2,700 scientists would participate in the Census on more than 540 expeditions around the world. They found nearly 250,000 marine species, upping the count by about 20,000; they estimate there are at least a million marine species in the oceans and tens to hundreds of millions of kinds of microbes.

There were schools of fish the size of Manhattan and animals that commuted like clockwork up and down the water column. There were living things in every bit of ocean the scientists looked at, from the deep dark depths to frozen seawater to waters so hot they would melt lead. There were mats of bacteria that extended for hundreds of kilometers.

But there was bad news, too. Scientists documented what used to live in the seas by checking historical records of sightings and catches, and also restaurant menus. Many species had declined in numbers, sometimes within one human generation. Phytoplankton, which sits at the base of the food web, has also declined in the last century.

This first Census is officially done, but it wasn't complete. The Census has no records for about 20 percent of the ocean's volume, and records are sparse for some large areas.

But the Census has already had a huge effect, not only in introducing us to thousands more of the species with which we share the planet (some were featured recently in our story Weird Creatures of the Deep), but also by setting a baseline against which we can measure our impact on the oceans. We fish some species too much, pollute the waters and change ocean chemistry through climate change. At least now we can get a good idea of how bad the situation is becoming.