Phylum: Chlorophyta   Family: Prasiolaceae

Prasiola stipitata  Suhr ex Jessen, 1848

Often found on sites nitrogen-enriched by seabirds and where otters mark their territories by sprainting. Not uncommon

References: 
Brodie, Maggs & John (2007) - Green Seaweeds of Britain and Ireland;
Burrows (1991) - Seaweeds of the British Isles, Volume 2 Chlorophyta