So I'm quite into foraging, and seaweed (the real thing not chinese take away stuff...) is supposedly very nutritious for you and very easy to forage up, but are there any seaweeds which are not edible, or possibly not worth eating, on UK shorelines?
There is one poisonous: the Desmarestia. The other species should be okay. However, I can't say anything about if they are "worth eating" :)
Desmarestia is a genus of brown algae found worldwide. Members of this genus can be either annual or perennial. Annual members of this genus can produce and store sulfuric acid in intracellular vacuoles. When exposed to air they release the acid, thereby destroying themselves and nearby seaweeds in the process. They are found in shallow intertidal areas.
So I went and asked Professor Michael Guiry, Director of AlgaeBase and world authority on seaweed. Here’s his reply:
“As far as I know, there are no really poisonous seaweed in this part of the world. “Our” Desmarestia species (4 of them and as you said mostly in deep water) produce sulphuric acid and can have a cellular pH of 2.
Anything else you might want to eat is free of poisons in the conventional sense as far as I am aware. However, care should be exercised when collecting in areas with high coliform counts and other bacteria, particularly in estuaries.
Further reading: blog post by Ginger Hultin