Receding storm in film of the open seas (7)
I believe the answer is:
pelagic
'of the open seas' is the definition.
(pelagic means relating to the sea)
'receding storm in film' is the wordplay.
'receding' shows that the letters should be reversed in order.
'storm' becomes 'gale' (a gale is a windy storm).
'in' is an insertion indicator.
'film' becomes 'pic' (short for picture).
'gale' in reverse letter order is 'elag'.
'elag' placed within 'pic' is 'PELAGIC'.
(Other definitions for pelagic that I've seen before include "of the ocean" , "Inhabiting the deep" , "Sea" , "Marine" , "Like an albatross" .)