Can My Crabitat Have A Waterline?

[DavidMandell]

I'm looking into obtaining some hermit crabs, and I maintain marine tanks. I don't have any large deep pools which would fit well in the aquarium I'm looking at (though I do have a shallower one for fresh water), but I do have a lot of aquarium salt, so I would like to create a saltwater paludarium and allow the saltwater to infiltrate into my substrate (which is oolitic aragonite sand). I would do regular water changes to maintain proper water chemistry and avoid the buildup of nutrients.

The problem is that while I've got about three inches between my waterline and the level of my sand (and can fairly easily adjust this if necessary), the guides I've been reading on this forum show that they dig a lot, and they dig deep. I do not want to drown crabs, and if they dig down to the very bottom to molt I am worried that they may. It would seem at first consideration that, being littoral creatures that must surely encounter waterlines in nature, they would be smart enough not to do so, but then again, the top of the beach is probably higher than three inches above the high tide line.

Does anyone have advice, and has anyone tried what I am trying before?

Thank you.

[Motörcrab]

Hi! I would personally avoid that. Crabs will generally molt away from the beach and tides in the wild. Once they shed their exo during a molt they are pretty much sitting ducks until their new exo hardens. If the water table would raise while the crabs exo is soft it's not going to make it.

Several years ago we had a flood in a tank. About an inch of water was at the bottom. One crab dug down in the front of the tank to the sitting water level and hung out on that spot. We lost a crab in that flood due to a bacterial bloom caused by the sitting water at the bottom.

Crabs generally need 6" of substrate depending on the size of the crab. Some species and larger crabs may need 10" or more!