Avengers of the Reef is a 1973 Australian children's film directed by Chris McCullugh and starring Simon Drake.
Scientist Bill Stewart goes to Fiji with his son Tim to investigate the appearance of the crown-of-thorns starfish in the reefs off the island.
He fails, but Tim thinks he has succeeded and runs away to an island village pursued by Kemp.
Tim makes friends with a Fijian boy, Sai, and is eventually reunited with his father.
[1] Anne Brooksbank won an Australian Writers Guild Award for her screenplay.