By Amy Campion
Summer on the Peninsula may belong to beach towels, backyard cricket and balmy bay swims, but one of our most astonishing natural spectacles arrives after the crowds go home.
As late autumn settles in and the water turns clear and cold, Blairgowrie’s shallows begin to stir. At first it looks like a shifting shadow beneath the pier, a slow darkening of the sand. Then you realise the seafloor is moving: thousands of Australian giant spider crabs are marching into the shallows, stacking claw-to-carapace in a mass migration to moult.
Native to southeastern Australia and found throughout Port Phillip, the crabs are both eerie and beautiful up close: long, jointed legs, a spiky camouflage-covered shell, and a stance that makes them look like something dreamed up by a storyteller.
Photo: Jules Casey
For most of the year they live scattered in deeper water, quietly cleaning the seafloor as they scavenge. But once a year, usually around the full moon in May or June, they gather in their thousands to shed their hard shells and wait for new ones to firm. In this moment of vulnerability they rely on safety in numbers, creating a carpet of crabs that looks almost unreal from above.
From the pier, the aggregation appears like a living cloud, rippling and reforming as the crabs climb over one another in restless stacks. Divers in thick winter wetsuits enter the water to swim among ‘crab walls’ several animals deep, while families wrapped in scarves lean over the rails to capture the astonishing sight on their phones. Some years the crabs crowd directly under Blairgowrie’s jetty; other years they favour Rye, reminding everyone that this is not a scheduled attraction but a wild and mysterious rhythm of the bay.
This coastline forms part of Bunurong (Boon Wurrung) Sea Country, cared for by countless generations of First Peoples of the Kulin Nation. Today, the Bunurong Land Council works alongside marine researchers, community groups and citizen science projects to protect and monitor the spider crabs, continuing the long tradition of connection, observation and custodianship of Sea Country.
In recent years, the spectacle has captured international attention, appearing in documentaries and filling social media feeds. This in turn has increased interest from divers, sightseers and recreational fishers, prompting calls for better understanding and management during the moulting period. Citizen scientists now help track sightings, movements and timing, contributing to research to protect the crabs and the ecosystem they’re part of.
For locals, the aggregation has become a seasonal marker, a reason to tug on a beanie, head to the pier, and fall in love with the Peninsula all over again. It’s a reminder that our most magical moments aren’t always framed by sunshine, crowds or summer holidays. Sometimes they arrive quietly on a cold still day, when the water is at its clearest and the bay reveals what it’s been hiding beneath the surface all along.
