Little squirts' identity parade

By Mike McKimm
BBC NI environment correspondent

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Sea squirts can be found all over the coast

Lift a rock at the low tide mark on any rocky beach in Northern Ireland and you'll find clumps of ascidians or sea squirts.

These apparently unremarkable creatures all look very similar. Some will be translucent jelly-like fingers, some will be round blobs or even flat splodges, fastened to rocks or other solid objects.

The big ones in particular have a habit of squirting out water when exposed to air and that's how they get their name.

To the casual seaside visitor they are hard to tell apart. And that is why the Ulster Museum organised an international ascidian taxonomy workshop at Portaferry on Strangford Lough.

For the best part of the week, they'll be examining local species and sharing their skills and experiences.

Sea squirts are filter feeders - they suck in and squirt out the passing sea water and from it they get the small planktons and particles they need to live.

But they weren't always static and stuck to some immovable surface; sea squirts start like as tadpole-like larvae and swim about.

When they reach the rock of their choosing, they attach themselves to it and start to metamorphose or change into their adult form.

An international ascidian taxonomy workshop is taking place

To do so they eat their brains. In effect it is like a tadpole turning into a frog - the tadpole's tail is absorbed back into its body.

Sea squirt larvae have a nervous system or cerebral ganglion which they absorb into their general cell structure as they mature.

Dr Clair Goodwin of the Ulster Museum, who helped organise the workshop, said: "Sea squirts are absolutely essential to the marine ecosystem and this workshop will be key in developing our knowledge of these little-known yet highly important creatures."

It is not easy to tell one sea squirt from another and often the exact identification has to be carried out in a laboratory.

And that is only possible if you know what you're looking for.

So international and UK experts had joined the workshop to share their expertise.

One of those is Gretchen Lambert from the University of Washington. She's been studying sea squirts around the world for 40 years.

Good news

And after a morning's examination at low tide on Strangford Lough she had good news for our local species.

"The only sea squirts we've seen here, I'm happy to say, are native species," she said.

"We've not found any invasive or non-native species here today. And that's all to the good. I hope it stays that way."

But the threat isn't that far away. Further north along the coast an invasive ascidian - or styela clava, was found in Larne Lough.

Having the experts check out Strangford Lough gives scientists a head start on tracking down any future aliens. And at least they'll know what they're looking for.