Phylum: Ochrophyta   Family: Fucaceae

Fucus cottonii  M.J. Wynne & Magne, 1991

Moss Wrack

A small fucoid of saltmarshes which looks brown en masse, but quite yellowish in close up. It can achieve large, dense patches, spreading vegetatively. Rarely recorded and confined to the north-west coasts of Scotland and sporadically around Ireland

References: 
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland