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IF this is Ulva linza, by any name, then AlanS should get agreements. However it may be impossible to tell from a single picture like this. Easy for me to write but Alan is an expert in this field - I am as close to a novice as it's possible to be with actually being one (my own opinion)!
ULVA LINZA - "Thalus variable in shape, from unbranched distromatic ribbons 1-8 cm wide and up to 30 cm long, characteristically ruffled or corkscrew-like, with hollow margins, tapering gradually or sharply to distinct hollow stipe, which may have marginal proliferations (linza morphology), to compressed branched tubes 0.5 - 10 mm wide (procera morphology), pale green in colour and....." etc. is from Green Seaweeds of Britain and Ireland◘
Bearing in mind the precision of this description (which progresses for four more paragraphs) I have also offered a less adventurous ID.
This is an old post but may resurface soon as an Other Observation because I am chasing some of the Ulvares - see http://www.ispotnature.org/node/689003
Lat/Lng: 50.156, -5.0711
OS grid ref: SW807329