So other reef gets damaged (9)
I believe the answer is:
therefore
'so' is the definition.
(I know that so can be written as therefore)
'other reef gets damaged' is the wordplay.
'gets damaged' is an anagram indicator.
'other'+'reef'='otherreef'
'otherreef' is an anagram of 'THEREFORE'.
(Other definitions for therefore that I've seen before include "as result" , "Consequently - for that reason" , "It follows" , "In consequence" , "Ergo" .)