Sea fruit? (4,5)
I believe the answer is:
crab apple
'sea fruit?' is the definition.
'crab apple' can be an answer for 'fruit?' (crab apple is a kind of fruit). I am unsure of the 'sea' bit.
'sea fruit?' is the wordplay.
'sea' becomes 'crab' (I am not sure about this - if you are sure you should believe this answer much more).
'fruit?' becomes 'apple' (apple is a kind of fruit).
'crab'+'apple'='CRAB-APPLE'
Can you help me to learn more?
(Other definitions for crab apple that I've seen before include "Wild fruit for jelly" , "unappetizing fruit" , "Fruit tree with sour bright red crop" , "Tart fruit for making jam and jelly" , "Small sour version of common orchard fruit" .)