One of the world’s most spectacular marine migrations is happening now on Melbourne’s front door step in Port Phillip Bay. UCF Director, Sheree Marris was lucky enough to witness this spectacular event that sees thousands of spider crabs come into the shallows to moult and mate.
All you need to do is head down to Blairgowie on the Mornington Peninsula equipped with a mask and snorkel or even a pair of swimming goggles to be a part of the action. In 2 metres of water, and as far as the eye can see spider crabs are clambering over each other and gradually building in numbers. The most common theory for this extraordinary behaviour is the crabs converge in the shallows where there is ‘safety in numbers’ so they can moult their hard exoskeleton (which is needed to grow bigger)… and then mate. During this process they’re vulnerable to predation and this behaviour increases their chances of survival and finding a mate.
There is much speculation around how many times this natural phenomenon occurs. One school of thought is that it’s only once a year, although crabs would need to moult more than once a year to grow to their enormous size. Perhaps it occurs more often and we’re just not out on the water enough to witness it (especially during the colder months here in Melbourne where drysuits are compulsory) .
What this demonstrates is how little we know about this unique environment and the many secrets that are yet to be revealed. It reinforces the importance of the Unico Conservation Foundation’s support for the Melbourne Down Under project which is raising awareness of the unique marine values of Port Phillip Bay and encouraging greater research efforts to be undertaken in the area.