Synonyms for Sea Wrack (same or very similar meaning)
WordNet sense 1 (submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts):
eelgrass, grass wrack, Zostera marinaWordNet sense 2 (growth of marine vegetation especially of the large forms such as rockweeds and kelp):
wrackFrom the ODE community, based on WordNetadd/edit