Hi Mat. Welcome to Ukaps!
I'm not sure you're asking in the right place for this. Firstly, the Technical/Help forum is for technical queries and problems concerning the website. Secondly, Ukaps is about planted aquariums and aquascaping. I know it's called the UK Aquatic Plant Society but its not really about aquatic plants of the UK, except where they can be used in aquariums. So I'm afraid you may find limited knowledge here on wild sea flora. That's not to say that no-one can answer your question but it's a little off topic.