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An underwater army of Spider Crabs are marching through Port Phillip Bay

Friday 13 April, 2018

Thousands of Giant Sider Crabs are making their annual migration to Port Philip Bay creating a weird and wonderful spectacle beneath the surface of the water.

Pictures and video footage showcasing the army of large orange crabs marching underwater shows exactly why we find the phenomenon so fascinating.

"Giant Spider Crabs can be found scavenging the ocean floor of Bass Strait and Port Phillip Bay, generally on their own. Once a year they gather in their thousands after they’ve moulted their hard outer shell, with numbers peaking when the moon is full. They need to moult to grow bigger but their new soft skin makes them vulnerable to predators such as rays and birds, so they band together to stay safe" says Parks Victoria Chief Conservation Scientist, Dr Mark Norman.

"We don’t know much about these crabs or their behaviour outside of their time spent moulting in our bay. It would be great if we could attach geolocators to some of the crabs. This would help us understand where they go after they have moulted."

While many cannot experience the spectacle in real life, Melburnians have the perfect opportunity to dive and observe the ocean bed crawling with Giant Spider Crabs this winter. Dr Norman explains that these crabs normally start moving into Port Phillip bay in January / February and leave towards the end of June or early July.

Many diving enthusiasts brave the cold each year to observe the migration and the moulting process of these crabs.

Divers frequently take the plunge around Blairgowrie Marina and Rye Pier hoping to see the Giant Spider Crabs. Surprisingly, many Melburnians don’t know that these huge crabs are moulting close to beaches around the Mornington Peninsula.

For more information on diving in Port Phillip Bay call 13 1963.

Media enquiries
Stephanie Zilles
8427 3466

Parks Victoria media centre