SYDNEY (Reuters) - Scientists studying Antarctic waters have filmed and captured giant sea creatures, like sea spiders the size of dinner plates and jelly fish with six meter (18 feet) tentacles.

A fleet of three Antarctic marine research ships returned to Australia this week ending a summer expedition to the Southern Ocean where they carried out a census of life in the icy ocean and on its floor, more than 1,000 meters (yards) below the surface.

“Gigantism is very common in Antarctic waters -- we have collected huge worms, giant crustaceans and sea spiders the size of dinner plates,” Australian scientist Martin Riddle, voyage leader on the research ship Aurora Australis, said on Tuesday.

“Many live in the dark and have pretty large eyes. They are strange looking fish,” Riddle told local radio.

“Some of the video footage we have collected is really stunning -- it’s amazing to be able to navigate undersea mountains and valleys and actually see what the animals look like in their undisturbed state,” Riddle said.

“In some places every inch of the sea floor is covered in life. In other places we can see deep scars and gouges where icebergs scour the sea floor as they pass by,” he said.

The Australian Antarctic Division expedition will help scientists monitor how the impact of environmental change in Antarctic waters, such as ocean acidification caused by rising atmospheric carbon dioxide levels, will make it harder for marine organisms to grow and sustain calcium carbonate skeletons.

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“It is predicted that the first effects of this will be seen in the cold, deep waters of Antarctica,” said Riddle.

“What we saw down there were vast coraline gardens based on calcareous organisms and these are the ones that could really be lost in an increasing acidic ocean,” he said.

The three ships, the Aurora Australis, France’s L’Astrolabe and Japan’s Umitaka Maru docked in Hoabrt on Australia’s southern island state of Tasmania, with their decks full of an array of sealife including unknown species of sea creatures collected near the eastern Antarctic land mass.

Some creatures, which were retrieved from between 200 - 1,400 meters (yards) below the surface, weighed up to 30 kg (65 pounds), while some 25 percent of the sealife chronicled was previous unknown.

The census of life in the Southern Ocean is known as the Collaborative East Antarctic Marine Census (CEAMARC). The French and Japanese ships examined the mid and upper ocean, while the Australian ship studied the ocean floor.

“This research will help scientists understand how communities have adapted to the unique Antarctic environment,” said Graham Hosie, leader of the census project on Umitaka Maru.

“Specimens collected will be sent to universities and museums around the world for identification, tissue sampling and bar-coding of their DNA. Not all of the creatures that we found could be identified and it is very likely that some new species will be recorded as a result of these voyages.”

CEAMARC is part of the international Census of Antarctic Marine Life, coordinated by the Australian Antarctic Division, which will see some 16 voyages to Antarctic waters during this, the International Polar Year (2007-2009).

The census will survey the biodiversity of Antarctic slopes, abyssal plains, open water, and under disintegrating ice shelves. It aims to determine species biodiversity, abundance and distribution and establish a baseline dataset from which future changes can be observed.