The bottom of the ocean often looks deserted, with sand and the odd seaweed covered rock all that can be seen. Not quite so in this video, taken near Melbourne. Diver PT Hirschfield captured an annual event, where masses of Australian Giant Spider Crabs congregate to molt their shells, seeking safety in numbers at this vulnerable time. They spread across such a large area that it’s impossible to see the seafloor. Credit: YouTube/PinkTankScuba