Day 10 of Life Beneath the Keel

On Sunday 13 September, at 1800 BST, The Island Trust is live streamingLife Beneath the Keel’ from Plymouth Yacht Haven as part of the Ocean Institute’s virtual Maritime Festival. This is the tenth in a series of blogs about the marine life we hope to discover then.

Day 10:  9 September 2020 | Sea squirts

This and the next three blogs concern Chordates. This phylum has three subphyla: Vertebrates (we will look at fish, birds, and mammals next); Tunicates (we will look at sea squirts today, salps we might find in the plankton); and Cephalochordata (lancelets for example, which we are not likely to find).

So, sea squirts are quite high up the taxonomic tree, they are our closest relatives so far discussed, being in the same phylum as us. You might be surprised to find the sea squirt here. It looks like just a tube, sucking in water at one end, taking what it needs out of it and squirting it out again, about as advanced as a sponge, you’d think. But in larval form (we might find it in our plankton trawl) it looks a lot like a little tadpole, with a head and tail, ready to grow into something with a spine. But it sticks itself to a rock, eats its brain then gets on with sucking and squirting and gives up on the idea of self-actualisation and discovering the meaning of life.

Some are solitary, like this fluted sea squirt, found in Howth Marina, RoI. And just because they’re squirty blobs doesn’t mean they can’t be pretty (image 1).

Others clone colonies like the star ascidians (image 2) and lightbulb sea squirts (which can also produce offspring sexually) (image 3).

Some are non-natives like the leathery sea squirt. It arrived on the North American West coast in the early 1900s, and probably came to Europe on the hulls of warships from the Korean war and then spread from naval ports on merchant ships and yachts. It is also present in New Zealand, Australia and Argentina (image 4). It is well protected against predators, able to withstand a wide range of temperatures and salinity, and being relatively large can outcompete other filter feeders. These factors make it a fouling problem on boats and fishing gear, and a threat to oyster and mussel farms.

John Hepburn, Ocean Discoverability Project Manager
9 September 2020