Beginning of summer affected island's seafood (6)
I believe the answer is:
scampi
'seafood' is the definition.
(type of seafood)
'beginning of summer affected island's' is the wordplay.
'beginning of' suggests taking the first letters.
'affected' becomes 'camp' (camp can mean exaggerated or affected).
'island' becomes 'i' (geographical abbreviation).
The first letter of 'summer' is 's'.
's'+'camp'+'i'='SCAMPI'
(Other definitions for scampi that I've seen before include "Large prawns as food" , "Crumbed prawns" , "Cooked Norway lobster" , "Large prawns cooked in batter" , "Dish of crustaceans" .)