Chris Mattison / Gutweed (Enteromorpha intestinalis) growing in shallow rock pool, Isle of Ulva, Mull, Scotland, June.

Philippe Clement / Gutweed / grass kelp (Enteromorpha intestinalis / Ulva intestinalis) washed ashore on Normandy coast, France, September

Alex Mustard / Black-lined periwinkle (Littorina compressa) on a bed of gutweed (Ulva intestinalis). St Brides Haven, Pembrokeshire, Wales, United Kingdom. British Isles. Irish Sea.

Philippe Clement / Gutweed / Sea lettuce (Ulva intestinalis / Enteromorpha intestinalis) green alga washed on rocky beach, Normandy, France, June

Philippe Clement / Gutweed (Ulva intestinalis / Enteromorpha intestinalis), sea lettuce (Ulva lactuca) and spiral wrack / flat wrack (Fucus spiralis) washed on beach, Normandy, France, June