A horde of hundreds and thousands of giant spider crabs have gathered off the shores of Melbourne in Australia. The spectacular gathering has been captured on video, which has now garnered more than 235,0000 views on YouTube.
Australian aquatic biologist Sheree Marris, who filmed the phenomenon with fellow scientist Jamie Seymour, said that thousands of giant spider crabs migrate to Port Phillip Bay each year.
This happens between May and July when the ocean water temperatures cool down, resulting in the sight of a blanket-like congregation of orange crabs crawling in the sandy shallows.
The reason behind this behavior is not clear but scientists think this has something to do with the process of molting, which happens when creatures such as insects, reptiles and arthropods shed off their outer layer or covering to form a new one.
Crabs are protected by an armor-like suit but they become vulnerable to predators such as stingrays and cormorants when they shed this hard outer shell. Scientists speculate that by gathering in large numbers and even stacking on top of each other and molting together, the creatures get protected from being eaten by hungry hunters.
"At times they kind of just stack on top of each other and the maximum I've seen is 10," Marris said. "But that's how deep it can actually get, which makes sense because if you're on the top, you're going to be more vulnerable, especially if they've just freshly molted."
Seeing the crabs aggregate in massive numbers can be a hair-raising experience in itself. The crabs are massive, with a body measuring almost 17 centimeters (6.7 inches) wide and claws growing to more than 70 centimeters (27.5 inches) in length. The yearly gathering likewise stretches for hundreds of meters.
Marris said that she has seen the gathering of crabs many times but the one they filmed is by far the biggest she has seen.
"This is a little video that I quickly put together for our The Nature of Science video channel," she wrote, referring to the video of the giant spider crabs. Marris hoped the video would raise awareness about the diversity of sea life in the southern waters of Australia.
"I've seen the aggregation so many times but it never ceases to amaze me. This was by far the largest I have ever seen and it's only going to get bigger and better as the crabs are still on the march."