Know Your Squirts and Ripples

Wakame is also known as Japanese kelp.  Image: Kathryn Birch CCW

Wakame is also known as Japanese kelp. Image: Kathryn Birch CCW

How much do you know about non-native species and the way they spread? Spend some time getting to know them and help the environment too.

If it is not diving into waste bins to see what boatyards are throwing away then it is peering over the sides of pontoons to see what non-native species might be lurking below!

It is an occupational habit for The Green Blue that we can’t take a walk along a pontoon without scrutinizing a pile or hull. Even this week we snapped Darwin’s Barnacle, often found on artificial structures and originally from Australia and New Zealand and discovered in the UK in 1945.

Some species have been in the UK for so long that you could easily mistake them for native plants and seaweeds. If you look at the bio-fouling on your hull, a pontoon or a fender you can be pretty sure there will be some non-native species in amongst it.

It is notoriously tricky to identify some non-native species; even marine biologists sometimes have to take a second look. With The Green Blue’s help you might just be able to spot one or two the next time you are near the water.

Wakame, also known as Japanese kelp and cultivated in Japan for cooking (think Miso soup), is a large golden brown seaweed first recorded in the UK in 1993. It has fingerlike edges and a holdfast frilled root and can foul jetties, vessels, moorings and buoys.

Tufty-buff bryozoan may look like seaweed but it is in fact a tiny colonial organism that grows to around 4cm. It can be found in dense populations in harbours and marinas, spotted as light brown bushy tufts and can be a nuisance on props and keels.

The Red ripple Bryozoan is something you might spot on a fender. It is actually made up of an intricate pattern of 1mm individuals that form a rigid sheet of red crust colonies often several centimetres across. As beautifully intricate and fragile as it may look up close, it can foul submerged boat hulls and, interestingly, is copper tolerant making it able to grow on some antifouled surfaces.

The Orange-tipped sea squirt was first recorded in the UK in 2004 and has spread around the coastline. It is translucent (so you can clearly see the gut inside), smooth with orange-tipped siphons through which water is drawn in and expelled or squirted.

And lastly, the Carpet sea squirt is firm, leathery and found in long orange cream coloured colonies. It has already caused problems in several marinas around the UK due to the way in which it smothers structures and other organisms, so real vigilance is needed to stop it establishing more widely.

There are over 90 marine non-native species in the UK, and over 20 are known to be invasive. As stunning and unusual as some of these species may be, it is important to remember that they are not native to the UK and some are invasive meaning they pose a real threat to our ecosystems, habitats, infrastructure and equipment. Recreational boats are one of several ways they can spread so we must stay alert and follow a few simple actions to keep them at bay.

Washing off your anchor before stowing and moving location is important, as is removing any visible fouling from your hull and equipment and putting it in the bin, not back in the water. And, of course, the annual lift, scrub and reapplying of antifoul is key to limiting the amount of growth.

The Marine Biological Association produces an excellent identification guide for selected marine non-native species. If you would like a free copy please contact The Green Blue on


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