There is actually one crab bigger than that one, but it lives in the ocean and and doesn't look nearly as intimidating.
Unless you frequent the many islands in the Indian Ocean, or the Cook Islands you are not likely to come across one. I have been a few places where they are said to live and have never come across one.
I am not sure how fast they are but I would bet that I could easily outrun it.
As a diver I would be much more worried about the the Mantis Shrimp...
With the force of a hammer’s blow, a mantis shrimp can smash the shell of a large snail that it then devours for dinner. In captivity, mantis shrimp have been known to shatter (1" thick) glass aquarium walls with their powerful kicks.
Scientists now report that mantis shrimp deliver their blows at speeds of up to 23 meters per second, making them the fastest “striker� in the animal kingdom. Much of the speed comes from a special “spring� in the hinge of the leg that does the kicking.
These little guys are nasty. Had one in my aquarium that was imported with some live rock. He struck a pencil hard enough to break it, and he was 2-3 inches long. I read an article where a marine biologist said that if they were 2 feet long (the largest get to 14") divers wouldn't worry about sharks anymore.
