Paddler used ocean first (8)
I believe the answer is:
canoeist
'paddler' is the definition.
(synonyms)
'used ocean first' is the wordplay.
'used' indicates anagramming the letters.
'first' becomes 'ist' (ist resembles 1st).
'ocean' with letters rearranged gives 'canoe'.
'canoe'+'ist'='CANOEIST'
(Other definitions for canoeist that I've seen before include "sportsman" , "Paddler" , "One using light boat" , "rower" , "Person who paddles a kayak or suchlike" .)