The break-up of the Larsen ice shelf in the Antarctic has opened up hundreds of miles of seafloor to a host of creatures and given birth to an ecosystem.

Scientists found the animals as they conducted the first survey of life on a seabed hidden by ice 650 feet thick until the shelf broke up. The expedition to the northwest Weddell Sea, including the open waters where the ice shelf used to lie, found an estimated 1,000 species of animal and plant life.

At least 20 species were new to science, including a giant amphipod and a sea anemone in a symbiotic relationship with a snail. The giant amphipod, which at 4in (10cm) long is one of the biggest found, was one of 15 previously unknown species of the shrimp-like creature found by the expedition. Other species that are believed to be new include four cnidarians, which are related to corals and jellyfish, and the sea anenome which acted as a defence system for the snail, which in turn provided locomotion.

Researchers were able to analyse the sediments on the seabed, and to take samples of the bacteria in the region. One of the most unusual features was a cold seep 2,625ft (750m) beneath the waves. It was covered in the shells of dead clams and appears to have become extinct or at least far less active in pumping out gases.

The findings are announced today by the Census of Marine Life to coincide with the launch this week of the International Polar Year which will see a range of research projects taking place to study the Arctic and Antarctic.

The ice shelf broke up in two sections, Larsen A in 1995 and Larsen B in 2002. With the 3,861 sq mile ice shelf gone, a vast number of cold-water animals have been able to move into the area.

Researchers were astonished at the abundance of life. Phyto-plankton and zooplankton have returned and their presence has allowed other life-forms, particularly krill, to recolonise the water and seabed.

Among the more spectacular creatures were minke whales and crabeater seals but it is the abundance of new life on the seabed up to 2,800ft (800m) deep that captured the expedition’s attention.

Julian Gutt, of the Alfred Wegener Institute for Polar and Marine Research, Germany, who led the expedition, said that the biggest surprise was the speed at which the seabed under Larsen B was being recolonised. “We found big amounts of sea squirts. This is a hint that the fauna of the sea floor is changing. In some places they were the most abundant organisms,” he said.

With more nutrients now able to sink to the seabed the area is expected become significantly richer in life. Watching changes in the ecosystem there could provide lessons for other parts of the world, Jesse Ausubel, co-ordinator of the Census of Marine Life, said.

“One of the questions about climate change is whether ecosystems will shift to new areas — will the north of the UK in 50 years have the same plants as the south today, or will there be entirely new ecosystems?” he said. “Observing what happens in the Larsen area could be instructive as to what happens elsewhere. It’s the birth of an ecosystem.”

Read Anna Shepard's eco-worrier blog

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