Seasquirts from across the world invade Britain!!

Perhaps we should avoid this 'tabloid headline' but it is an interesting fact that at least two species of that intriguing group of animals known as sea squirts have travelled the world and now appear on our shores.

What is a sea squirt or ascidian?

These fascinating marine creatures appear in a wide variety of shapes, colours and sizes sometimes singly or in colonies which are attached to a hard surface. Some look like lumpy sponges and others like tough bags of jelly. A soft body sac containing the vital organs is enclosed in a protective tunic hence the other common name of 'tunicate'. Organic food particles are filtered by entrapment onto mucus from the water which is wafted in a stream through one siphon before leaving through a second hole.

Whilst they appear to be similar to more primitive creatures such as sponges, sea squirts have developmental characteristics of back bone and nerve chord that link them to animals such as fish, birds and you and me! Remember this when you next peer at one on the sea-shore!

Leathery sea squirt
Styela clava
Height up to 12cm with wrinkled
creamy brown blotchy tunic

The most widespread of the two Far Eastern invaders is the Leathery sea squirt Styela clava. This probably arrived in the 1950s on the hulls of ships returning from the Korean war as it was first noticed in the vicinity of naval dockyards. Look out for a stalked, club-shaped body up to 16cm high, with a blotchy, wrinkled, leathery tunic which can be found now amongst stones and seaweed on some sheltered Cornish shores including those of the Helford River.

Your sharp eyes are needed to locate a more recent introduction

Who will be the first person to spot this one on Cornish shores?

Dr John Bishop explains what to look for.

"The Far-Eastern ascidian Perophora japonica (no common name as yet) was reported from NW France in the 1980s and was found in a marina in Plymouth Sound in 1999. Since this occurrence was publicised, it has been recorded from The Fleet, Dorset, Guernsey and Milford Haven. P. japonica therefore seems to be an addition to the list of species from Japan and Korea that have become established in the UK. The Marine Biological Association, the University of Plymouth, and the Station Biologique de Roscoff are undertaking a study of P. japonica. To date we are unaware of records from Cornwall, and would appreciate hearing from anyone who finds it.

P. japonica is a colonial ascidian with small spheroidal zooids (the individual members of the colony) c. 4 mm high, arising from creeping stolons. Its most distinctive feature is the presence in summer of clusters of bright yellow terminal buds, which are angular and commonly star-shaped. These buds have not been reported in the native species P. listeri, or any other Perophora species. The Plymouth specimens of P. japonica, when alive, have a marked yellow or greenish-yellow coloration in younger parts of the colony; the zooids may be densely packed or spread out along the growing stolon. Colonies grow on a wide range of substrates.

Perophora japonica
each body is similar in size to one whole lentil
or a very small pea (très petit pois!).
Look for the bright yellow tips as the colony
clusters on the surface of
sea weeds, sponges or debris.

Colour images of live specimens are on the MarLIN web site (http://www.marlin.ac.uk)." If you find something similar please try to take a photograph or make a sketch and log the place, date, time and tide. John will be happy to help make the identification so contact me leaving your name, address and telephone number - P E Tompsett, Awelon Colborne Ave, Illogan, Redruth, Cornwall TR16 4EB, 01209 842316. E-mail petomp@bioscope.demon.co.uk or Dr John Bishop, Marine Biological Association of the UK, Citadel Hill Laboratory, Plymouth PL1 2PB, UK, E-mail: jbis@mba.ac.uk.

Extract from HVMCA newsletter No.28 Spring 2004