Melbourne divers were surprised to see spider crabs migrating to Port Phillip Bay on February 25, an annual migration that normally occurs from May to July as ocean waters cools, according to ABC Australia.

Chiharu Shimowada has been diving for over 10 years, but told Storyful she had never experienced anything like this. When she went diving, many crabs had congregated and could be seen tearing apart what looked like an octopus, an event which can seen in the video.

“This spectacular natural phenomena is well known amongst Melbourne diving community…The crabs stay [in] [the] very shallow waters, so anyone can go and see this amazing event,” Shimowada said. Credit: Chiharu Shimowada via Storyful