Some of them anyway. The thing I quickly learned is that these crabs have different personalities and the behaviour of one does not represent the behaviour of all. Some are definitely worse than others. Much worse.
Case in point, in the early days of the tank I had two medium sized crabs that were caught from a rockpool in Llandudno. One of them was calm and caused no trouble. The other was a constant source of aggro and had a menacing demeanour at all times. If I put my finger near the glass he’d rush over wanting to fight me. The other one had no interest in me except when it was feeding time and it would scurry over and grab the end of the turkey baster to chug down the mysis shrimp on offer.
The aggressive one though? Constant trouble. One morning I came down and found it eating a prawn. The prawn was dead, so I didn’t know if the crab had found it or killed it. I gave it the benefit of the doubt, because I struggled to believe it would be able to catch a healthy prawn. A week later the same thing happened, only this time the prawn was still very much alive. The crab had definitely nabbed it. Not because it was hungry – it had been eating like a king – but because it could.
I managed to free the prawn but sadly it didn’t recover from the ordeal. I decided there and then that unfortunately the crab had to go back where he’d came from. The other crab, who was the same size, had caused absolutely no bother at all, but I assumed that could change at any time so I returned them both to the pool where I got them from, with one hell of a tale to tell their crabby friends.
I picked up a couple of smaller crabs to replace them, thinking they wouldn’t be able to do much damage. Wrong. Interestingly though, again it was one crab causing mayhem and the other was no bother. Like the larger one before him (or her), one of them just had an air of constant menace about it. It was always harassing anything that came within its grasp, stealing food from the anemones (crabs seem to have have no fear of anemones, even the larger ones) and it would always run across the tank with aggressive intent. It never seemed to be calm or chilled, and if it was sitting still you knew it was only because it was stalking something.
Again, strangely the other crab showed none of that aggression. It moved slower and generally kept itself to itself. They are the same species but behaved completely differently.
The trouble maker was just always into something. No matter how often I put food in the tank, it didn’t seem to matter. It would be trying to rip open a muscle, or it would be tearing a snail apart. My hermit crab disappeared around this time and my guess is he was eaten by this guy. Once again, a prawn was killed so again I returned both to the place they came from (in this case, New Brighton).
Maybe I could have kept the one that had caused no bother, but it didn’t seem worth the risk. I also had a couple of smaller crabs in there and while they were no trouble, I lost one of them to a Blennie. I saw it happen too, the crab had buried itself in the sand but it started to re-emerge and as I watched, curious as to what it was doing, the largest of the Blennies (only a couple of inches long) suddenly grabbed it and started trying to tear it to pieces.
One can only assume that the crab had shed its shell and was in its peeler state and therefore vulnerable, as it had survived alongside the Blennies for several weeks until that incident. Although I managed to free it from the jaws of the Blennie, a prawn then attacked it! A prawn!! I couldn’t believe it.
I isolated the little crab hoping it would recover but it didn’t make it. If they aren’t eating they’re being eaten. The sea is a brutal place.
It’s a shame they are just so unruly and anti-social as shore crabs add real character and entertainment value to the tank and I loved watching them. Unfortunately some of them are just an absolute menace and not suitable to life in a peaceful aquarium.
Update: After returning two of the crabs to New Brighton, the very next day the Hermit Crab showd up having been missing for weeks, so at least that’s one murder the shore crab wasn’t guilty of.
