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.