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

Animal of the Week -- January 14, 2008

Good morrow good women and gentlefolk,

It was a most pleasing moment last week when a colleague forwarded me a link to a news story, not about a pair of twins getting married (http://news.bbc.co.uk/1/hi/uk/7182817.stm), but about a Pacific giant octopus playing with a Mr Potato head (http://news.bbc.co.uk/1/hi/england/cornwall/7179368.stm). The giant mollusc loves his toy, mostly because it's got crab meat inside it (which is a feature I don't recall from the Mr Potato Head that I had), but also its bright colours and moving parts. Now, as you might guess, the Pacific giant octopus (Enteroctopus dofleini) is a big octopus, reports of a 272 kg, 9 m, specimen are highly doubtful, but a 71 kg live specimen is confirmed. But it turns out that this size record is rivalled among the octopodes by a bizarre freak of the molluscan world -- this week's animal of the week is Haliphron atlanticus (the seven-arm octopus). Of which a dead specimen weighed in at 61 kg, giving an estimated live weight of 75 kg, and had a mantle length (the head-like bit) of 40 cm.

What? I hear you cry. How can there be such a thing? Surely this septapode octopus is a contradiction in terms, and cephalopod oxymoron, a lie, a fabrication, a genetic freak or frankenstein fish. No, I tell you, it is real, a proper species.

The truth is that the distaff representatives of the species have the full complement of octopus legs; but once more, in the face of all we expect to be true about the natural world, the males are missing a limb. In octopuses (please, not octopi) and other cephalopods (squids, cuttlefish, and nautili), the males have a specially adapted limb, the hectocotylus, which is used to deliver sperm to the female. In many other octopuses this arm is larger than the others, but in the seven-arm octopus, this sperm arm is small and coiled up in a small pouch underneath the right eye. During the act, the male unfurls his arm from beneath his eye and makes a special delivery to a cavity under the female's gelatinous mantle. So I guess, "giving her the eye", means something much more intimate in octopus courtship than in human relations.

Bye then!

Peter Hayward
Head Keeper
Animal of the Week