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Looks a little like decomposing Fucus spiralis
I think F. serratus - in the original photo the fronds are clearly serrated.
Dictyopteris polypodioides has been suggested; that species has membraneous, translucent fronds whose margins are entire.
I will agree with JoC.
Although a while ago, I remember identifying Serrated wrack (and don't know why I did not use that) so somewhere between identifying it and posting it I had a brain fart - I goofed.
I am not familiar with site etiquette and management. Do I now need to and can I remove my original identification?
Lat/Lng: 52.1366, -10.0523