Marine scientist (13)
I believe the answer is:
oceanographer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">marine scientist</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for oceanographer that I've seen before include "One who studies the seas" , "Marine scientist" , "One studying the great seas" , "Scientist concerned with the seas" .)