Gathered in large numbers around the wild seas (6)
I believe the answer is:
massed
'gathered' is the definition.
(I've seen this before)
'large numbers around the wild seas' is the wordplay.
'large numbers' becomes 'md' (I can't justify this - if you can you should believe this answer much more).
'around' indicates putting letters inside.
'the wild' indicates an anagram.
'seas' anagrammed gives 'asse'.
'md' going around 'asse' is 'MASSED'.
'in' is the link.
Can you help me to learn more?
(Other definitions for massed that I've seen before include "Gathered together in crowd" , "Congregated" , "Gathered or assembled in large numbers" , "Grouped together" , "formed a large group" .)