A swimming Swimming Crab

(For licensing or usage, contact I was diving Waimea Bay on the North Shore of Oahu. I came across a depression in the sand and went down to investigateit. I found a crab (that goes by many names and is usually found around the shallow waters of the mangroves). I started filming with my GoPro:and finished recording it (displaying the typical defensive to move on). All of a sudden, the crab swam straight up about 20 feet and then started swimming away. It caught meby surprise and started recording again while trying to catch up to it. I have never seen a crab do that.