Intertidal seaweed. Fronds of serrated wrack seaweed Fucus serratus, growing low down on the intertidal zone of shores. The name serrated wrack" derives from the saw-tooth edged blades. White dots on the fronds are openings known as cryptostomata. Seaweed is a marine algae, some species of which float freely in the sea and some, as here, are found attached to rocks on the shore. Photographed in the Highland region of North West Scotland."