Ridge of coral (4)
I believe the answer is:
reef
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ridge of coral</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for reef that I've seen before include "Submerged rocks" , "Ridge of rock or sand just below sea surface" , "one gathered on yacht" , "Sandbank" , "Shallow coral ridge" .)