Iain Macdonald, SNH Policy & Advice Officer, tells us about the mysterious seaweed that’s making its way up the west coast of Scotland.

Wireweed growing in a rockpool, Great Cumbrae. ©Lorne Gill/SNH

I had been aware of wireweed for some time. How long for I don’t really know, certainly for quite a few years for, as seaweeds go, wireweed is one of the more distinctive. I can vaguely recall images of it when I was a child, possibly in the late 70’s, probably taken in Spain or Portugal. I don’t know why, but I also seem to recall the word “Japanese” forming part of the name, but that might be confusion on my part with Japanese knotweed, something completely different.

Fishing out a line of wireweed. ©SNH

In photos wireweed is sometimes held proudly aloft, out of the water as if it were some form of trophy. It isn’t, it resembles a washing line with lots of pieces of dirty brown, torn washing. Not that attractive a description you might think, but if you look at the photo above you might just see what I mean. “Once seen, never forgotten.” However I had not given wireweed any subsequent thought for about 30 years until I needed to revisit it as a part of SNH’s Species Action Framework (SAF).

When SAF started there was a suspicion that wireweed might even be spreading along the Scottish coast, but we didn’t know if that were true. We didn’t even know where the wireweed was. That might not have been a big problem, had there not been some evidence from elsewhere that wireweed likes living in Europe and can compete with native seaweeds. By changing the structure of a coastal area, the community of animals and plants living in an area might also change. This was much more than “just to do with seaweed”.

Wireweed, the alien invasive seaweed growing on the shoreline. ©Lorne Gill/SNH

The “issue” with wireweed is that whilst it might look at home on the Scottish coast, in reality it belongs to the Pacific. That includes Japan, so perhaps my memory is not completely gone? There is an unproven theory that wireweed might have hitched a ride to Europe with Pacific oysters in the 1960s or early ’70s when oysters were introduced for shellfish farming. However wireweed first arrived in Europe, by 2004 it had appeared in Scotland, at Loch Ryan to be exact, possibly via Ireland; and by 2013 wireweed had reached North Uist.

Even if we know where it is what can we do about wireweed? I asked myself that question, and then I asked colleagues. The answers were much the same, “not much”. Once in the marine environment it is simply not feasible to remove every part of every frond which is either attached to the Scottish coat or floating around it. Even if we could remove wireweed from Scotland, we would also need to remove it from neighbouring countries, otherwise it would just come straight back. It looks like wireweed is here to stay.

Although SAF as a stand-alone project has ended, work on non-native species continues. Recent Scottish legislation to control the release of non-native species into the wild is among the toughest in the world. European legislation has also been strengthened. Interesting times indeed.

You can find the SAF Handbook chapter on wireweed  here.

The SAF project relied upon volunteers telling us where the wireweed was. Some citizen science surveys for you to consider taking part in are:

Coastal – Capturing Our Coast

Non-native species – The GB Non-Native Species secretariat

Scottish native species – A list of surveys published on the Atlas of Living Scotland