ok seriously, crabs by nature are opportunistic feeders, many when young feed on algaes (mythrix). yes this can be benefitial to an aquarium, but remember that in the ocean there is a lot of room to move around. these young crabs will graze hereand there taking their favorite lil bits and move on. in a confined environment they cannot do this. therefore they will be forced to eat more food in one area, thus they will look harder for something they really want. if this means pulling your prize Zo' out like dandylions form your lawn just to see if there is something good hidden between them,,,they will. if they find a tasty morsel on your sinuaria, they will think there is more, so they can dig into it trying to find it, reguardless of the damage inflicted on the sinularia.
now these crabs are getting older, and bigger, their diet is changing, their bodies require more protiens, what has more protien than algae?...yup, flesh, now opportunity becomes a factor once again, if they can get the same protien from snatching up a snail and spending 10 minutes eating it as they would get from 2 hrs of grazing,,,,bye bye snail. if they find small fish sleeping (remember crabs are night active also) fish could very well be on they menu. i have even seen small holes in larger fish that came froma crabs eating on them while sleeping. (some tangs can be sound sleepers....the sea monkeys got my money)
so in my few deacdes of reefing i have come to the conclusion that crabs belong in the ocean, or on a plate, but not in a reef tank. even the most placid lil "oh he has never caused a problem" crabs, has a demon inside, the demon of opportunity and sooner or later the moment will come, and for us when it does....its too late.
