Animal of the Week -- November 10, 2008

"The sea has its large rivers like the continents. They are special currents known by their temperature and their colour. The most remarkable of these is known by the name of the Gulf Stream. Science has decided on the globe the direction of five principal currents: one in the North Atlantic, a second in the South, a third in the North Pacific, a fourth in the South, and a fifth in the southern Indian Ocean. It is even probable that a sixth current existed at one time or another in the northern Indian Ocean, when the Caspian and Aral seas formed but one vast sheet of water."

So mused Professor Aronnax aboard Captain Nemo's Nautilus in Jules Verne's Twenty Thousand Leagues Under the Sea.

It is such rivers that helped this week's animal, Megaleledone setebos become the forebear of many species of deep sea octopus. A study from the Census of Marine Life show that this unassuming octopus of shallow Antarctic waters is the likely forebear for many diverse species of deep-sea octopuses. Researchers believe that ocean currents, such as Professor Aronnax's rivers, carried larvae from the shallow Antarctic waters to the deep sea where, in isolation, and under the new selective pressure (quite literally in the deep oceans) they diverged into separate species. The idea that a living species is the ancestor of others is mighty exciting. It's like stumbling across the last common ancestor of chimps and humans alive [Have you been to Norfolk lately? -- Ed].

The development of these rivers, or thermohaline expressways, is associated with expansion of the ice caps, as fresh water is sequestered in ice caps, concentrated cold salt water sinks helping to create the currents that then flow into the deep oceans -- carrying species from shallower waters with them. Successive periods of activity of these currents related to global warming and cooling create successive waves of immigration to deep sea areas leading to a greater diversity.

As cold waters sink away from the poles, warm waters are pushed and drawn towards them, hence the Gulf Stream keeps the UK and other parts of northwestern Europe, which should be as cold as Canada, ice free. As human-generated global warming melts the ice caps, the Gulf Stream may be disrupted, actually causing temporary cooling of the British Isles and Norway... before we all fry, starve, and die in wars over access to water and Ambre Solaire.

Happy days