Ocean census identifies tiny creatures with a massive role

They are the smallest animals in the sea and they form a vital link in the web of marine life but scientists know next to nothing about the zooplankton of the world's oceans.

A deep-sea trawl by marine scientists has come up with hundreds of species of zooplankton - from tiny shrimp-like creatures and swimming worms to flying snails and pulsing jellyfish.

A scientific expedition to the Sargasso Sea of the North Atlantic has catalogued about 500 species of zooplankton living at depths of between half a mile and 3 miles below the surface.

The 20-day cruise was designed to capture some of the most important, but overlooked, creatures of the oceans that play a vital role in both the marine food chain and the carbon cycle. "We're trying to really make a census of what actually lives in the ocean," said Dr Peter Wiebe, a senior scientist at the Woods Hole Oceanographic Institution in Massachusetts.

"In order to say anything about how climate change affects the ocean we really need to know who's living there," Dr Wiebe said.

The research is part of the international Census of Marine Life and was designed to explore the little-known area of the Atlantic between the south-east American coast and the mid-Atlantic ridge, which runs like a spine along the ocean floor.

"Among the 1,000 individual organisms identified at sea, our team of 28 experts on board found what appears to be several undescribed species that may well prove new to science," Dr Wiebe said. "We are charting the plankton in the sea like astronomers chart the stars in the sky. With the zooplankton chart, we can assess what changes - man-made and natural - are taking place in the largest habitat on earth," he said.

Many zooplankton feed on the plant plankton that absorbs carbon dioxide from the sea surface where it has dissolved from the atmosphere. Zooplankton often deposit this carbon deep in the ocean where it can remain for many thousands of years - thereby acting as an important "sink" for atmospheric carbon dioxide.

The zooplankton had to be gently trapped in fine-mesh nets before being brought to the surface, where an organism's DNA "barcode" could be analysed in a laboratory on the research vessel.

Ann Bucklin of the University of Connecticut, a member of the research team. "We are just starting to realise how little we know about species variety. We used to think we knew many species well, but the advent of DNA barcoding has radically altered that perception," Dr Bucklin said.

"The zooplankton census is enlarging human understanding of the pattern, flow and development of life in the sea."