Marine algae (7)
I believe the answer is:
seaweed
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">marine algae</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for seaweed that I've seen before include "We eased (anag)" , "What may be cast up on shore" , "Marine plant" , "What's seen at the coast" , "Laver perhaps" .)