The quality of the sea Italy's in perhaps (8)
I believe the answer is:
salinity
'the quality of the sea' is the definition.
(I've seen this before)
'italy's in perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'italys'+'in'='italysin'
'italysin' is an anagram of 'SALINITY'.
(Other definitions for salinity that I've seen before include "Saltiness" , "The quality of the sea" , "state of the sea" , "Characteristic of main" , "Brine's characteristic" .)