Mini Fiddlers behavior

Hi,

I have got around to resetting up my 120 gallon tank, and for a lark decided
set up a palludarium design this time. I placed a top "beach" at about half
way up the tank. This goes a full 4 feet across, and has about 6" of
submerged low water area. The land has a hill of dirt, with a sandy beach,
and a filter "waterfall" in the corner. Underneath I have river rock
bottom, on top of a PVC pipe under gravel filter. That sets on potting
soil. The tank population is:

2 Black Mollies.
2 Silver Mollies.
2 Red wag swords.
3 Guppies (1 female 2 males).
2 Golden mystery snails.
2 Mini fiddler crabs.

This combined with 3 aquatic grasses of unknown type . On top I have
some house plants as well.

I got the crabs on Sunday. I had only one choice in females at the
shop,and ended up with a much larger male than I really wanted. He is about
three quarters of an inch body, at least an inch and a half toe to toe. She
is small, no more than an inch toe to toe, probably more like three
quarters. Well, all day Sunday The big boy decided the beach was his, and
stayed under the water chasing the silver female molly around. The girl
skirted up the dirt, and over to the back of the ground, and through a crack
dropped to the bottom of the deep tank. They both took to scavenging, and
looking for food. By later that night she came up to the top and was
sitting on a rock with the male. That morning, they were both in deep side,
the male in the "cave " (the part under the land) and the girl under a large
rock in the open area. Later that day I found the male standing next to a
supporting rock waving his claw around, and the female tucked down under it.
That was the last time I saw her. Now I saw the male has burrowed under the
supporting rock, and is happy under there.

So, is this normal behavior? Has the male made a lunch for himself? I
know they burrow, but I thought it would be on the dry side, not under
water.

Also I hope to get more crabs, but am unsure of the ratio of males to
land area. Will it stress them to have multiple males there?

And finally, what are others thought on this tank and loaches? Would
Kouli or clown loach, or a spiny loach do well in this environment, or would the
fiddlers create problems with them?

Thanks,

Paul.
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