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An old post maybe but I'm here because it's in our interest to try and get these things right.
I believe this to be Bladder wrack because of the elongated shape and general bifircation of the Receptacles. More importantly there are gas bladders bottom right. One other seaweed has warty receptacles like these (F.Sprialis) but they are usually nearly round, erring to heart shaped.
There's a lesson here - wracks are commonly mistaken for each other, so it always best to have within a photo, a frond which carries the, usually paired, bladders on the flat fronds - see http://www.ispotnature.org/node/691361
THREE MARINE PROJECTS
Lat/Lng: 50.156, -5.071
OS grid ref: SW807329