Islands in North America beset by decay (8)
I believe the answer is:
canaries
'islands' is the definition.
'north america beset by decay' is the wordplay.
'north america' becomes 'na'.
'beset by' indicates putting letters inside ('beset' could historically mean 'cover').
'decay' becomes 'caries' (dental caries).
'na' inserted into 'caries' is 'CANARIES'.
'in' is the link.
(Other definitions for canaries that I've seen before include "Atlantic islands - cagebirds" , "holiday resort" , "Small yellow finches" , "The birds can arise" , "Mediterranean islands and yellow birds" .)