Seafood source arranged by East Dorset (6,3)
I believe the answer is:
oyster bed
'seafood source' is the definition.
'oyster bed' can be an answer for 'source' (I have seen 'Source of pearls ' mean 'oyster bed' so perhaps 'source' could also mean 'oyster bed'). I'm unsure of the 'seafood' bit.
'arranged by east dorset' is the wordplay.
'arranged' is an anagram indicator (letters rearranged).
'east' becomes 'e' (abbreviation).
'by'+'e'+'dorset'='byedorset'
'byedorset' anagrammed gives 'OYSTER-BED'.
Can you help me to learn more?
(Other definitions for oyster bed that I've seen before include "stew, perhaps" , "Source of pearls" , "seafood supplier" , "A source of seafood" , "breeding ground" .)