Build taming coral. Lead it in. Build pillers around it until it can't move at all. Build catapult and place up high to shoot down at karkinos. Hit top of body. The karkinos body will move downwards and rebound when hit correctly. Shoot carefully as they die easily. Good luck
Tranq Arrows/Darts DO NOT WORK!!! To knock this out you need to use a catapult and shoot in only on it's back. If you shoot it on it's legs it will kill it. UP-VOTE SO EVERYONE KNOWS & TO GET DODODEX TO ADD THIS!!!
A catapult turret is the way to go with this Crab! Get it up close and blast its body with rocks! Be careful of where you aim, because if you hit it legs, it will take massive damage! You might want to lay down a trap so it doesn't scuttle away.