By Mark Kinver
Science and environment reporter, BBC News
Many of the world's deep-sea octopuses evolved from a common ancestor, whose closest relative still exists in the Southern Ocean, a study has shown.
Researchers suggest that the creatures evolved after being driven to other ocean basins 30 million years ago by nutrient-rich and salty currents.
The findings form part of a decade-long global research programme to learn more about life in the world's oceans.
The first Census of Marine Life (CoML) is set to be completed in late 2010.
The project, which began back in 2000, involves more than 2,000 scientists from 82 nations.
The research into the evolution of deep-sea octopuses was part of a programme called the Census of Antarctic Marine Life (CAML), explained Ron O'Dor, CoML's co-senior scientist.
"Many of these octopuses were collected from the deep sea by a number of the CoML's different projects," he told BBC News.
"All of that material was brought together and made available to Dr Jan Strugnell, a biologist at Queen's University Belfast, and she used this material to carry out DNA studies.
"She was looking at the relationship between these different deep-sea octopuses and how they originated.
"She has been able to trace the timeline for their distribution back 30 million years to a common ancestor."
The species could all be traced back to a shallow-water octopus that lived in the Southern Ocean. Today, the creature's closest living relative (Megaleledone setebos) can still be found in the icy waters around Antarctica.
Dr O'Dor added that Dr Strugnell's work also enabled her to identify how changes in the region's ocean played a pivotal role in the development of the new species, especially the emergence of a "thermohaline expressway".
"When you get an increase in sea ice, fresh water forms ice crystals and leaves behind high-salinity, high-oxygen water, which is denser than the surrounding sea water, so it sinks," he explained.
We can use the first census as a benchmark to see what happens in the oceans over the next decade or more
Dr Ron O'Dor,
CoML's co-senior scientist
"It gets mixed by sea currents and flows into all of the deepest parts of the ocean.
"At the time this process started, there was no oxygen at the bottom of the ocean, so it brought oxygen into these areas, and we can now see that the octopuses moved out from the Antarctic into deeper water."
Dr Strugnell's work, supported by the UK's Antarctic Funding Initiative (AFI) and the National Environment Research Council (Nerc), also showed how the creatures adapted to the new deep-sea environment.
One example was the loss of their ink sacs, because there was no need for the defence mechanism in the pitch black waters.
As well as being one of the CoML's highlights, the research is also being published in the journal Cladistics on Tuesday.
The deep-sea octopus study, along with dozens of other projects, form part of the census's fourth progress report, which will be presented at the World Conference on Marine Biology, which begins in Valencia, Spain, on Tuesday.
The overarching objectives of the global collaboration between CoML's scientists include:
- Advancing technology for discoveries
- Organising knowledge about marine life, and making it accessible
- Measuring effects of human activities on ocean life
- Providing the foundation for scientifically based policies
Dr O'Dor said that the main focus of the CoML for the remaining two years was to "synthesise" the data.
"Many of our projects have already completed their fieldwork and we have a lot of information," he observed.
"What we are now trying to do is to bring all that information together in a form that allows the public to understand how much we have learned about the ocean and what lives in it."
As far as improving our understanding of life beneath the waves, Dr O'Dor said: "It has been successful beyond what I imagined when I first became involved.
"It will provide a baseline. We are not going to know everything about what is happening within the oceans, but we have samplings of most marine habitats.
"We are moving into this period of global warming, which is resulting in the acidification of the oceans, melting of the polar ice cap.
"We can use the first census as a benchmark to see what happens in the oceans over the next decade or more."
Meeting formally for the first time at the five-day gathering in Valencia will be the CoML's Science Council, which will take an overview of the 10-year Census.
"Over the past few years, there has been huge public interest in biodiversity because there is a legitimate concern about the changes being caused by humans," commented Patricia Miloslavich, the Census's co-senior scientist.
"The Science Council will (consider) what people have said about areas that have not been explored or taxonomic groups that have been overlooked in the past," she told BBC News.
"We have had this first census that has given outstanding and amazing results for many ecosystems and regions.
"But now that we have been able to identify where there are some gaps, we would like to explore these areas."
Dr Miloslavich added that the Science Council will also develop the objectives of the second census, which will run from 2010 until 2020.