Wild Ocean Blue

Christmas is here and I couldn’t resist writing about one of the most festive ocean inhabitants, the Christmas Tree Worms.

Xmas tree worm. Photo by Alain76

It’s their outrageous headgear that gives the Christmas Tree worms their name. Most of the worm we don’t see. They hide their rather normal-looking segmented bodies inside boulders of coral. But each worm has a pair of frilly bits called radioles, which they poke out of their burrows to sift food and oxygen from the water.

These scuba-divers’ favourites can put on eye-popping multicoloured displays on coral reefs, like forests of miniature Christmas trees.

Xmas tree worms covering a coral boulder. Photo by will48324

Creep up slowly on one and it will stay out and let you peer closely at its extraordinary spiraled protuberances that can be yellow, orange, brown, blue, red, or white or almost any colour at all. Waft a current of water past them and they flicker out of sight. (I admit that I like to watch for a while, then play magician, waving my hand above them and watching them disappear).

Xmas tree worm. Photo by Tim Sheerman-Chase

So, how do these festive critters take up home in coral in the first place? Well, they may look like nothing but feather dusters, but these hermaphrodite worms come fully equipped with reproductive organs and from time to time will shed sperm and eggs into the sea in the hope they will collide with each other, mixing the gene pool up a little. The resulting larvae then drift through the water for a while before finding a patch of coral they like the look of, settling down and building a chalky tube to live in. The coral polyps then grow around the worm until it is embedded inside the coral skeleton.

And of course these critters don’t come out only at Christmas, but you can see them decorating reefs all year round.

Xmas tree worms. Photo by Nick Hobgood.

As well as looking irresistibly pretty, Christmas tree worms might help to protect corals from attack by canivorous crown-of-thorn starfish, shoeing away any hungry predators that get near, tickling and irritating their sensitive undersides.

Anyway, I think that’s enough facts for Christmas (although do scroll down to the end for some more if you want them), so I wish you all a very HAPPY CHRISTMAS 2009 and leave you with some more photos of these wonderful beasts. Enjoy!

Xmas tree worm. Photo by sarsifa.

Xmas tree worm. Photo by jtu.

Xmas tree worm. Photo by Nick Hobgood.

In detail:

• The Latin name for Christmas Tree worms is Spirobranchus giganteus meaning ‘enormous spiralled gills’. How apt.
• Christmas Tree worms are serpulids, a type of polychaete worm.
• Their radioles grow to about an inch tall.
• There are considered to be two subspecies of S. giganteus, one living in the Indo Pacific the other in the Atlantic and Caribbean. Both subspecies come in a range of colourmorphs.
• Study of the protective role of Christmas tree worms. De Vantier et al, 1986.
• Study of the different colours of Christmas tree worms. Song, 2006. The most popular colour is white.
• Christmas tree worms can live for over 40 years.

Now that I’m back from snowy adventures in the Swiss Alps (under the guise of giving a graduate seminar on science communication – not bad at all) I must tell you about the latest episode of the BBC’s Life series. Because this week they went underwater again, and it was brilliant.

Centre of attention were the invertebrates, a crazy diverse group of ocean critters that get up to all sorts of tricks and never fail to amaze.

Among them were big-brained Australian Giant Cuttlefish.

Giant australian cuttlefish. Photo by Jacob Bridgeman

We watch on as the huge males (up to half a metre long plus tentacles) attempt to woo the opposite sex by putting on a flashy colour display and getting in raucous fights with each other over who’s boss.

Less well-endowed cuttlefish males adopt a very different strategy for passing on their genes to the next generation: cross-dressing. Not very macho, admitedly, but it does the job nicely. By mimicking female colouration, the little males can wander into the mating arena without being chased off. The dominant male thinks he’s lucked out with another female showing up, while in fact the intruding male gets a chance to nip in and mate with the real female. Clever, eh?

Sticking with the cephalopods, we also revisit the Giant Pacific Octopus we met in the first taster episode.

Giant Pacific Octopus. Photo by Schristia

The female lays thousands of eggs inside a cave, tending them like a conscientious farmer tends his crops. It’s such a gargantuan effort for the female that as soon as her young have hatched, she dies. But now we discover that the story of the octopus doesn’t end there.

We get a glimpse of the gruesome reality of what goes on beneath the waves when a giant Sunflower Star (a huge variety of starfish) arrives on the scene – sped up by time-lapse photography – crawls into the cave and drags out the dead mother octopus using thousands of sucky tube feet. Sunflower Star plus a gang of other scavengers swarm over the dead body getting a good feed. It’s not pretty, but it is important, otherwise the oceans would soon fill up with dead octopodes lying about the place.

Sunflower Star. Photo by Ed Bierman

Scavenging echinoderms also make an appearance in an extraordinary Antarctic scene (you can watch this clip outside the UK). The time-lapse photography is simply stunning, as we watch the sea floor crawling with colourful starfish (and rather terrifying three-metre carnivorous worms). All very pleasant until we find out what brought them there: a dead baby seal. But like I said, the world needs its carrion-eaters, scavengers and recyclers to clear things up for us.

In this underwater episode of Life we also see jellyfish eating jellyfish, peep at some on the invertebrate wonders of the coral reefs (including boxer crabs – so cool!), and watch on as herds of spiny Spider Crabs gather together by the thousand to moult and, pairing up, they tumble across the floor in a tight mating clinch.

And I’m now convinced that I don’t ever want to find myself amid a gang of Humbolt squid. If ever there was a creature in the ocean to be a bit wary of, then these are most definitely them.

A razor-sharp, flesh-ripping beak and 70,000 hooks on each one: that’s quite enough to put me off. And it seems they are very clever beings, communicating with flashes of red across their bodies.

Humbolt Squid. Photo by MBARI 2006

But I would like to go diving beneath the Antarctic sea ice. Hang on for the making-of segment at the end of the episode to find out how the film crew took the astonishing footage of the starfish scavengers. An enormous drill makes a tunnel through eight-feet of ice, opening up an eerie blue doorway for the divers to plunge through to another world, somewhere I would certainly like to visit.

And so, once again, the BBC have gathered together some eye-popping footage that serves to remind us just how wonderful, diverse and surprising the oceans can be.

Thank you BBC.