Diving in Fiji: 2006

Scuba Diving Fiji

An adult orange clownfish (Science and S.R. Thorrold)
About 60% of the young orange clownfish found their way home

The remarkable homing instincts of some coral reef fish have been revealed.

A team tagged two species of reef fish larvae to see where the juveniles were going after spending weeks and even months maturing in open sea.

It found most of the orange clownfish - made famous by the Finding Nemo movie - and vagabond butterflyfish returned to the reef where they had first hatched.

Writing in the journal Science, the team said the discovery could have implications for marine protection.

'Marine fish lay very small eggs, and when they do, they are released into the water column,' explained co-author Professor Geoff Jones from James Cook University in Queensland, Australia.

'They develop into a really tiny little larvae that we think drift around in the water currents, sometimes for months.

'The missing link in our understanding of coral reef fish has always been: where do the larvae go?'

Help from Mum

But until now, finding this out has been extremely tricky - attaching tags to miniscule larvae is not an easy task.

So the international team of researchers tackled the problem by getting the mother to help.

Satellite image of the Kimbe Island (Science)
The study "

Scientists go hi-tech to save coral

At cold depths, the rate of growth is very slow

Less is known about the floor of the world's oceans than the surface of the Moon.

It is only in the past few decades that technology allowing humans to peer into the previously uncharted depths has become available to scientists.

Remote Operated Vehicles (ROVs) and manned submersible craft have opened up to exploration a whole new world of deep marine ecosystems.

One of the most startling discoveries has been the number of coral reefs living hundreds of metres beneath the surface, in temperatures ranging from 4-13C (39-55F).

The existence of cold-water corals has been known since the 18th Century, but the vast number of reefs found in the deeper reaches of the world's waters has amazed researchers.

Yet just as scientists are beginning to understand the significance of the coral to the surrounding environment, they are also witnessing destruction.

'Glacial' growth

Environmentalists point the finger of blame at the fishing industry and the practice of bottom-trawling with drag nets.

This method of fishing involves scouring the sea bed with huge nets that are some 60m-wide; they are held apart by two huge metal plates weighing up to five tonnes.

Submersibles have brought a revolution in understanding

"It's heavy gear, and the reefs and the coral colonies are very fragile and easily damaged," Jan Helge Fossa, chief scientist at the Norwegian Institute of Marine Research, tells TVE's Earth Report programme for BBC World.

"So it was quite obvious that this was an activity that couldn't go on," he adds.

Cold corals are very slow growing. Some individuals are estimated to be up to 1,800 years old, and many reefs began forming at the end of the last Ice Age.

Damage inflicted by bottom-trawling can result in catastrophic consequences for the species living amid the reefs.

Onboard the institute's research vessel, Dr Helge Fossa is leading a survey for cold corals off the northern coast of Norway.

Robot eyes

The Institute provides advice on the marine environment to the Norwegian government, which is one of the few nations that have introduced laws to protect cold-water corals.

After performing a multibeam sonar sweep that provides a real-time map of the search area, the team launches a ROV through the side of the ship.

I have never heard a person in Norway, after looking at the videos, who objects to protection

Dr Jan Helge Fossa,
Norwegian marine scientist

Once the vehicle reaches the site 200m below the surface, its four powerful lights allow the onboard camera to beam pictures back to the scientists on the surface.

"What we see here is only coral rubble, and it's trawled out to small pieces," Dr Helge Fossa observes. "We have so far seen no live coral."

It is not long before the prime suspect is located: discarded trawling equipment. Closer inspection reveals that the nets and gear are likely to be about 20 years old.

Norway's Coral Act 1999 protects all coral reefs in the nation's waters from intentional damage, and bottom-trawling has been completely banned in areas surrounding five specific reefs.

However, the country has the longest coastline in Europe, making monitoring and policing the region a tough task.

Video campaign

To date, there have been no prosecutions from data gathered by the space-borne Vessel Monitoring System (VMS), but Dr Helge Fossa's team hopes images obtained by its high-definition submersible-camera system will help change that.

The Norwegian expedition finds evidence of discarded gear

"We know that it is important to get our results out, not only to the government but also to the public," he says. "That's why we use a lot of videos, it tells more than a thousand words."

He said it made people understand why the complex ecosystems needed protecting: "I have never heard a person in Norway, after looking at the videos, who objects to protection."

Some scientists believe that other nations should adopt similar protection measures as Norway, otherwise many more deep cold-water reefs will resemble a lunar surface.

The Television Trust for the Environment's (TVE) Earth Report - Cold Corals Deep will be broadcast on BBC World on 21 and 23 October 2006. Please check schedules for further details