There is a variety of marine algae on rocks of the upper shore at Waulkmill Bay on West Mainland in Orkney, including common olive green fucoids like Bladder Wrack and bright green Gut Weed. But I noticed a seaweed that I hadn’t seen before on the west side of the beach where the environment has a mixed salinity regime. Salt water and fresh intermingle where Mill Burn drains from Loch Kirbister, and from the saltmarsh known as Skaith, prior to emptying across the shore into the sea. These are just the right conditions for Horned or Estuary Wrack (Fucus ceranoides) to grow. It is characterised by a flat evenly forked frond with pointed forked apices and a well-marked midrib. Rounded air bladders are absent but elongated pockets or air may develop in the tissues of the frond (Bunker et al 2017).
Bunker, F. StP. D., Maggs, C. A., Brodie, J. A., Bunker, A. R. 2017 Seaweeds of Britain and Ireland. Second Edition, Wild Nature Press, Plymouth, UK