You haven’t lived until you have sat on the sea bed in the middle of metre-high swarms of thousands of Giant Spider Crabs, each crab bigger than a basketball!
Not your cup of tea?
Then have a look at the video taken recently near Rye in southern Port Phillip. (Thanks to Karl Bromelow).
These remarkable crustaceans spend most of the year widely spread throughout the bay, their shells covered in growths that makes them hard to see. They are scavengers, eating almost anything they find and helping to keep our bay clean.
They come together to breed before the winter moulting season, the really exciting bit ….
Crabs can’t grow to the next size without shedding their rigid external skeleton. First they secrete hormones to loosen the shell from their skin. Their shells have weak suture lines that burst open and let them wriggle out, leaving the old shell on the sand like a discarded suit of armour.
If you look closely at a washed-up crab shell, you will often see the symmetrical, even edges of the shell where it has opened up. These crabs are probably still alive, if they survived the next handful of hours after moulting.
Freshly-moulted crabs are orange-coloured and clean. Their body is like jelly until they pump themselves up to the next size with fluid, and their new shell can harden. Until then they are easy pickings for predators because they are so soft. They also can’t move properly until their muscles re-attach to the new, next-size up shell because their shell is also their skeleton!
There is a survival advantage being in these huge circulating groups – each crab spends less time being exposed to predators. Images thanks to David Donnelly (DRI Research Officer/Two Bays Whale Project).
It’s just one more example of how wonderful our bay really is.
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