26 March 2012

Wireweed near Mewslade

Gareth Thomas wrote: 'SS 42385 86742 takes you right to the large pool at half-tide where I found  Japanese Wireweed (Sargassum muticum) on Wednesday last. Main features are the feathery fronds with match-head sized flotation capsules throughout. It originated from Japan - probably from imported oyster spats to oyster farms. It is very prevalent on the Irish coast, and also in Scotland. Not aware of it in Gower...
Japanese Wireweed (c) G. Thomas
The NBN Gateway shows that Japanese Wireweed was first recorded in our area in 2003 when the CCW Phase 1 intertidal team noted it in Port Talbot Harbour. It was subsequently found at Pwlldu in 2004 again by CCW and then Bracelet Bay in 2008 by Judith Oakley. It seems to widespread, though localised around the Welsh Coast, though not sure about the record from Ynysybwl!


Judith Oakley said...

Hi, I have been recording and monitoring marine non natives around Swansea and Gower for some years. Sargassum muticum has become much more widespread in the past 2 years. I have recorded it from Bracelet Bay, Oxwich, Port Eynon, and Worm's Head Causeway in increasing amounts.
Thanks for your record Gareth. Could you clarify how many plants you saw and were they growing on rocks? Also, do you have a GPS reference? It is also worth recording whether there was any other flora/fauna attached to the fronds, and also if you find any un-attached plants washed up anywhere. Please let me know via Barry Stewart. Many thanks, Judith Oakley, Consultant Marine Biologist

Anonymous said...

Hi Judith
This is the second time I have tried to comment - first one did not get recognised.
Sorry no GPS ref, but if you type in my OS ref into this site:
It will take you straight to it.
It is the largest pool by far in the mid-tide rocks.
The weed is all growing from a rocky/sandy bottom in 2-3ft of water. There are probably 20 plants or so, and they mostly fan out at the surface and create small rafts of micro-bubbles of transpiration. Only they show this, so on a sunny day you can count the plants by the patches of bubbles.
This is a pool I have known for 65 years and I would say the weed was not there last year.
I have not found any not attached, but have not searched for it.
There was a small shore crab C maenas? living in the sample of weed I brought home to photograph
I hope this one gets thru. Gareth

Judith Oakley said...

Hi Gareth
thanks very much for your information. You'll have to come out on one of my summer 'Seashore Safaris' on Gower!
keep on recording and reporting your finds. best wishes, Judith

Judith Oakley said...

what I forgot to say is you should be extremely careful removing Sargassum from the shore. You can compost it but shouldn't let it get in to any water courses. I have had a trial removal/monitoring project on Gower. This involves following a strict protocol as leaving any part of the plant on the rocks or in pools will enable new plants to grow, even from fragments. I am hoping we may get tproject going again this year and will let you know.