This is extreme low water at a spring tide - feet and cameras rarely get here. We're into the Laminaria digitata beds that are usually below the low tide mark.
View of the Laminara beds at low tide. The smaller seaweed is Fucus serratus, saw wrack.
Mid-beach, the saw wrack shares the beach with the green Ulva lactuca (sea lettuce) and Cladophera rupestris, a green algae which looks reddish brown here.
Around the high water mark amost every other species is displaced by bladder wrack, Fucus vesiculosus.
At high water, no algae can establish themselves on this rock: