Skating facility shortly opening by sea (5)
I believe the answer is:
'sea' is the definition.
'skating facility shortly opening by' is the wordplay.
'skating facility' becomes 'rink' (ice rink).
'shortly' means to remove the last letter.
'opening' means one lot of letters goes inside another (some letters open a gap in others).
'rink' with its last letter taken off is 'rin'.
'rin' put into 'by' is 'BRINY'.
(Other definitions for briny that I've seen before include "Of salty water" , "Salty; (the) sea" , "The main" .)