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Page last updated at 09:56 GMT, Thursday, 26 November 2009
Monster worm and sea star frenzy
Matt Walker
Editor, Earth News

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A starburst of life (in timelapse)

Deep under the Antarctic ice, a rare, colourful burst of starfish and 3m-long monster worms has been filmed by a BBC camera crew.

Filmed in time-lapse, the extraordinary swarm of deep-sea creatures gathers to feed in a frenzy on the body of a seal, which had sunk to the ocean floor.

Such a bounty of food may only occur once every ten years in the ice-cold waters of McMurdo Sound, Antarctica.

The images were taken by divers filming for the natural history series Life.

Descending through a hole cut in the ice, cameramen Doug Allan and Hugh Miller set up a time-lapse camera on the ocean floor.

The time-lapse sequence revealed the feeding frenzy of hundreds of huge worms, starfish, brittle stars and sea-urchins.

Under the Antarctic ice
Long way down

Nemertine worms, also known as boot-lace or ribbon worms, belong in their own phylum, the Nemertea.

Some species are scavengers or herbivores, but most are voracious predators, catching prey using a proboscis that shoots out from their mouth. The proboscis may be poisonous or even tipped with a sticky secretion, depending on the type of worm.

In Antarctica, such worms often feed on clams and shellfish.

However, they also congregate with starfish, which are also called sea stars, to feed on seal droppings.

In the sequence filmed for the Life series, the invertebrates gather in a frenzy to feast on a seal carcass that has sunk to the ocean floor.

So much food may only arrive in one place once in a decade.

The nemertine worms (Parbolasia corrugatus) are able to puncture the seal's skin with their proboscis, opening up the carcass, so that worms and marine isopods such as woodlice can enter to feed.

The starfish feed more slowly - by pushing out their stomachs through their mouths.

As a sea star pushes its stomach against the seal's skin, it secretes digestive juices that dissolve the seal's tissue.

Sea stars
A burst of sea stars

Sea urchins, such as Sterechinus neumayeri, also get in on the act.

Like the giant worms, this species comes in a variety of colours.

Not only does it sometimes camouflage itself with bits of shell, but it can live for up to 40 years.

Because of the cold temperatures, many creatures under the ice grow extremely slowly. But by doing so, they can reach a great age and a great size.

Starfish touching arms
Touching moment

In temperate and tropical seas, other more common predators dominate, such as crabs.

However, the fossil record shows these animals vanished from the waters of Antarctica about 35 million years ago, when the continent cooled.

Today, Antarctica has no lobsters or crabs. There are also few fish, such as sharks and rays.

Instead strange animals lurk there, including sea urchins, sea stars, giant worms and large underwater sea spiders, which can grow up to 30cm across and live for several decades.

However, last year researchers warned that if global warming continues, it will put this unique marine life at risk.

Nemertine worm
A nemertine worm's deadly proboscis

In the last 50 years, sea surface temperatures around Antarctica have risen by 1-2C, which is more than twice the global average.

That could encourage crabs to colonise the region, followed by fish such as sharks, which are capable of decimating the local wildlife.

If that does happen, the Antarctic seafloor would no longer be dominated by soft-bodied, slow-moving invertebrates, which are believed to be similar to those found in ancient oceans prior to the evolution of shell-crushing predators.

'The Deep' episode of the BBC natural history series Life will be broadcast at 2100GMT on BBC One on Monday 30 November.



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