Phylum: Ochrophyta   Family: Fucaceae

Fucus serratus Linnaeus, 1753

Toothed Wrack

Large carpets of this seaweed are found at the lower shore just before the kelp starts. Male and female plants are separate. The common name is derived from the serrated edge of the fronds, and they have no air bladders

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland