Crustacean collapse will come about if biosecurity finally reversed (8)
I believe the answer is:
crayfish
'crustacean' is the definition.
(I know that crustacean can be written as crayfish)
'come about if biosecurity finally reversed' is the wordplay.
'come' becomes 'crash' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'finally' suggests the final letters.
'reversed' says the letters should be written in reverse.
The last letter of 'biosecurity' is 'y'.
'if'+'y'='ify'
'ify' in reverse letter order is 'yfi'.
'crash' placed around 'yfi' is 'CRAYFISH'.
'collapse will' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for crayfish that I've seen before include "little nipper" , "Lobster-like crustacean" , "Freshwater crustacean" , "Edible crustacean" , "Lobster-like creature" .)