Phylum: Chlorophyta   Family: Kornmanniaceae

Blidingia marginata (J. Agardh) P.J.L. Dangeard ex Bliding, 1958

Very common and an early coloniser. Found in the upper tidal zone on a variety of substrates

References: 
Brodie, Maggs & John (2007) - Green Seaweeds of Britain and Ireland