Glasswort

The forest of little plants growing in the water on the local salt-marshes and mudflats are Glasswort Salicornia europaea. 
Wort is a very old name and has been in use since at least the 9th century. Chaucer uses it in his 14th century Canterbury Tales, in the Clerk's Tale: "Whan she homward cam she wolde brynge Wortes or othere herbes tymes ofte."
Wort as part of a plant's name usually indicates that it was once used in herbalism or for other practical uses. This is certainly the case for glasswort,  in the past its ashes were used for making soda-based glass.