Secrets of the deep sea

20 July 2006

How do some deep-sea creatures grow to giant size? And how is Earth's ocean abyss similar to a desert island? This week, marine experts gathered in Southampton to share the secrets of one of our planet's most mysterious habitats.

Antenna dives in for a roundup...

Image: Lance Horn, National Undersea Research Center

The deep-sea isopod is a giant of the ocean. At 45 centimetres in length it towers over the shallow-water isopods, which grow to about 5 centimetres.

Image: NOAA

How is the deep sea like a desert island?
The deep ocean is home to a horde of exotic creatures, including some colossal critters that dwarf their shallow-water siblings. But how did these deep-sea giants evolve?
Ocean experts say they've got a new theory. They believe it's because living in the deep sea means animals are isolated, a bit like on a desert island.
Biologists studying land-dwelling creatures have long believed in the so-called 'island rule'. This says that when animals evolve on inaccessible islands, small animals become larger, and larger animals become smaller. But until now, we didn't know that ocean animals adapt to their environment in a similar way.

Look at the difference between these three medium-sized shallow-water snails and the three tiny deep-sea snails.

Image: Craig McClain

To test the 'island rule' for deep-sea animals, a team of ocean experts compared the sizes of snails from shallow and deep waters. Sure enough, smaller shallow-water snails tended to have larger deep-water relatives, and deep-sea snails with large shallow-water relatives tended to be smaller.

A deep-sea stone crab living on a blue whale bone on the ocean floor.

Image: Craig Smith

Whaling latest
Covering more than 60% of the Earth's surface, the vast deep sea is the largest habitat on the planet. But this exotic world is under threat from human activities such as whaling. So far, deep-sea scientists have identified 28 new species that depend on whales for food.
When a whale dies, its body sinks to the ocean floor, creating an island-like habitat for deep-sea life that can last for decades. But whaling is destroying these communities of creatures and one ocean expert believes that some species may already be extinct because of it.
'We need to recognise that the oceans are made up of a stack of tightly connected communities - overfishing or pollution in surface waters is bound to cause problems thousands of metres below.'
Craig Smith, ocean expert, University of Hawaii

Craig Smith, ocean expert, University of Hawaii

Image: Craig Smith

Broadband Version

This video was shot in the deep ocean west of Shetland. Squat lobsters are actually not lobsters at all - they're more closely related to hermit crabs and other crustaceans.

Video: Scott McGinn

Spotlight on Earth's ocean abyss
There's still much to be discovered at the bottoms of our oceans. This film footage of a squat lobster catching and eating krill is a first for marine science. Catching this behaviour on camera for the first time helps ocean scientists better understand the secrets of the deep.

Broadband Version

This potentially new species of squid was spotted in the deep sea of the Gulf of Mexico.

Video: Tony Kastropil

Watch this unidentified species of squid swimming 10,000 feet below the ocean surface. Marine scientists believe this monster from the deep might be a totally new species. The deep sea is full of mysteries - who knows how many new species there might be down there?

Broadband Version

This footage of a swimming shrimp was filmed 2000 feet beneath the sea's surface. Some species of shrimp can survive in depths of over 13,000 feet.

Video: Tony Kastropil

Watch this shrimp swimming through the lightless depths of the Gulf of Mexico. Close-up video like this helps ocean experts identify new species, and it can also help them capture the way marine creatures move in the high-pressure waters of the deep sea.
What's next?
These secrets of the sea give us a glimpse of the vast unknown world in the depths of our oceans. But there's no doubt that when the world's leading marine scientists meet again next year, they'll have unravelled many more mysteries from the deeps.
If you'd like to get closer to the unusual and colourful creatures that live in our oceans then make sure you catch Deep Sea 3D (PG), which is narrated by Johnny Depp and Kate Winslet and is now showing on the giant screen at the Science Museum IMAX 3D Cinema.
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