Reef explorer's gear (5)
I believe the answer is:
scuba
'reef explorer's gear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scuba that I've seen before include "breather" , "Sort of diver" , "Skin-diving apparatus" , "Skin-diver's device" , "Device that lets divers breathe under water" .)