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Yet another un-reef you guys must be getting tired of me

Fiddlers are not really very common pets over here, so I'm a bit lost. Actually, I guess crabs in general are a bit scarce in the mainstream market.

The ones I'm looking at are small, about 2cm across the carapace seems to be the upper limit, full salt, from a muddy mangrove esturine area with barely any water movement save for the tides. Burrows are between high and low waterline, usually near rocks or in between mangrove shoots. The crabs seem to eat out of the water, diving for cover in any available burrow when there is a sign of danger. (took pics, should have them tomorrow)

I'm looking to mimic the natural environment as much as possible (not that specific one, a better one!) only with less rotting mud and no tides. The only experiences I've had with providing land access has been for climbers and explorers, which these aren't. They are more scuttlers/burrowers. I'd like to arrange something where there was access to land for out-of-water digging, feeding and general crabbiness.

The issue with this is that even shallow moist sand is FOUL. The last thing I want is to have the poor guys burrowing into toxic sand. Still, I do want to provide them with opportunity to dig.

I also want to keep the water nice and given that the water cannot realistically fill the entire tank due to the need for land access, this could be tricky with a sand substrate. I could see it working with grit or pebbles etc, but sand would kick up in the current. HOBs wouldn't work because of the length of draw (I don't want the platform too close to the lid, crabs are crabs after all) and I don't know how well air-driven would go. Could I maybe get away with something gentle and air-driven (thinking UGF with pebbles) given it'll be about 4cm of crab total, or is that just nowhere near enough regardless of stocking?

Oh, and you know how I gave in on the LR front before, well this one can't really go there. It can also be any colour you like, providing it is brown Crabs on shellgrit and coral just doesn't look right, y'know? They need a certain muddiness.

So far I have considered the following:

*a pebble/grit base, stacked (like pancakes) rocks for climbing, and no dig

*pebble/grit base, meshed box (to keep water between pebbles clean) filled with pebbles with ramp setup for out of water access to moist pebbles. Possible pump in mesh box for filtration, using pebbles as media. again, no dig.

*hand-built polystyrene/riversand 'rock' with crevices and a stacked appearance as well as a shallow (2cm?) crater at the top for housing sand. Possible pump hidden behind with outlet somewhere to allow water down from mid-way. Still has issue of dry sand or stagnant wet sand. Substrate whatever as pump can draw from higher up and avoid sand turbulance.

*as above, but centre of 'rock' is hollow with fine mesh/course fabric hammock and very fine gravel/course sand to allow some water circulation through deeper areas.

*sand base with mishmash of driftwood/mangrove root wood for climbing/scuttling/perching.

*'turtle tank' setup with pebble substrate, a glass landing pad on rear wall and possibly a feeder dish of dry sand.


That is where I'm at. All of those would be completely workable with fresh, but the salt thing is throwing me off as I'm not sure how far I can push it. Sticking with standard rules of 30x turnover, shellgrit base, choc full of LR and with a skimmer, well, it'd just be unworkable. This has to be different and I'm just not certain how different it can be.

Any and all help appreciated

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

For digging I'd mix a sugar fine aragonite type sand and some crushed coral/shells(anything with many different sized peices for burrow making). You can buy this stuff(and should), so it shouldn't be toxic....dunno if you were worried about the stuff you had access to collect or what would happen to it in the tank?

They also make a produce called mineral mudd that you could use. This stuff is supposed to grow macroalgae really nice, so maybe throw in some macros and a mangrove shoot or something.

Just make sure to get as fine a substrate as possible, these guys are used to digging in mud after all.

I'd mix that with some of the rocks from their natural environment if you can. Those would probably be the right types and since you are collecting the animals from the same place, there shouldn't be any harm....at least I think you're collecting. Then I'd just let a section of the rock/sand stuff come up out of the water. Maybe pile up the rocks on one side of the tank and pour the sand/crushed shell mix or mineral mudd over that side. You should have a half/half tank. should look nice and accomplish the task IMO.

Umm...I'd say for filtration that UGFs have no place in a SW tank. I'd use anything else that you can pull out and clean. That said, sponge filters aren't the best alternative either, but at least you can pull them out and clean them a little. Plus, bubbling and SW makes a big ol' nasty mess of salt creep.

In all honesty, you are only housing a couple crabs, so the bioload won't be that great. So your filtration doesn't have to be that great either.

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Critical Fertilator: The Micromanager of Macronutrients

Yes, still collecting. I don't know anyone who stocks these. I've been good and paid all my licensing fees, but this only extends to livestock so I'll have to look into the rocks. They appear to be diced granite so should be easy enough to acquire elsewhere.

No way on earth would I collect stuff from where these guys are. If they weren't getting their own tank, I wouldn't even be considering them. It is semi-industrial and the coastline is just revolting. The water is very turbid and slicked in areas. The smell is not your typical healthy mangrove, and the washed up debris... well lets just say the crabs won't be missing anything much.

I was worried about problems in regard to stagnant wet sand in trying to give them a place to burrow outside of the water, and the depth of sand needed underwater to provide full body coverage. Normally that'd be a no-no what with gas pockets etc.

I haven't seen the mud for sale here, but I'll keep an eye out, it looks useful! Would there be a problem with overdoing the nutrients if there is nothing to take it up? I'll look for easy macros but mangroves are a no-go due to them being protected.

Aragonite is generally a creamy white colour, yeah? If I can't find it in a darker colour, could I mix it with sifted riversand (essentially just silt) to get the appearance a bit closer without having compaction issues? Or the mud, would that work still?

Yeah, UGF was a long shot. It was more from the perspective that it'd be very low movement and trap less junk than a device that'd give decent filtration. I'm iffy about sponges and crabs and sponges and salt, so it'll probably just be a pump of some sort.

Ta for the help

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

I think as long as you were to mix any of the sand up every now and again, it wouldn't be a problem getting stagnant. Plus, the burrowing effectively reduces the anaerobic areas in the sand. Many reports have been made about how burrowing animals improve the health of sediments in mangrove areas. Don't know why it would be different in a tank.

I think the best part of those mineral mud products is that the nutrients are locked up in the substrate components until a plant's root is able to tap into it. They are used safely in reef aquariums, so I doubt they leach nutrients.

Aragonite is usually whitish, yes. I'd try to recommend something with a calcium carbonate base, just for pH buffering reasons. However, if you keep up with waterchanges, it should be ok to use a silicate type sand in this non-reef venture. You just might end up with diatom blooms is all. I doubt your crabs would care though. I'd avoid anything labeled as silt, that can contain many nutrients (being a clay). I'd go for one of the two mentioned above or use the mineral mud type product.

I'd look into some macroalgae whatever substrate you get. It will help keep the water clean and tends to harbor free reproducing snacks for whatever fauna you have in a tank.

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Critical Fertilator: The Micromanager of Macronutrients

callatya, if you are worried about anerobic posckets, i wouldnt stress them to much... you could an should add mangrove cuttings (they are available through aquabid and ebay). this will reduce anaroebic pockets and nutrients etc overload... actually with enough established mangrove peices, you could get away with out a filter at all. they will sap out all the nitrates, nitrites and ammonia. so you should research that (along with weekly or bi-weekly water changes). but your set ups shoudl do well. also if yo could get some rocks from the natural enviroment (or smilar) you could build a retaining wall with the rocks and have the burrowing area sloping up frot he wall... also you could weekly mix up the sand, taking some of the embankment sand and switching it with the submerged sand... there are also marine trumpet snails that could help you to keep your substrate shurned, but there specs could differ from that of the crabs'.

hope my two cents worth helps.
GOOD LUCK

\\\\\\\"an ounce of prevention is worth a pound of the cure\\\\\\\"

I have a feeling that fiddlers do not continuously make new burrows, which would not allow the substrate to turn over regularly, which would cause anaerobic pockets to form eventually.

One possible way to do it is have normal gravel or small stones with PVC pipes in it as false burrows. I'd predict that fiddler crabs would pretty easily learn that the burrows are safe, even if they didn't dig it themselves, although that's a prediction I make without having kept them. Keep in mind that even normal gravel can become anaerobic if deep enough and not mixed enough. But at the same time it won't foul as quickly as sand.

brandeeno's got a good point, plants will help bring oxygen down to lower levels of substrate. But IME, a nice healthy fiddler crab habitat reeks of anaerobic bacteria, even when filled with plants.

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The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.

I'm not really sure that the "anaerobic" nature of the substrate is as big a concern as we've made it out to be here.

I've had my 'fuge going with 5-6" of sugar-fine aragonite for 2.5 yrs now. It's never gotten to the point where it could be smelled. I'm sure there are plenty of anaerobic areas, and they aren't causing any problems. In fact, I'm pretty sure thats the DSB idea. In the deeper portions of the sand, nitrate should be consumed for it's oxygens and released as Nitrogen gas.

The top layer of a fine sand substrate should accumulate detritus, and should be used by aerobic bacteria. But detritus shouldn't be able to reach the anaerobic areas. I beleive that if it did, that's when you get some foul smells, and why gravel would be a BAD idea.

This is all SW mumbo jumbo, mind, and I don't really know if a similar bacteria function in a FW environ. The whole deep sand bed issue has been debated quite fiercely, and thus, there's lots of info to be had, but it's hard to say all is reliable. A recent Coral magazine article had some very interesting and common sense info. It talked about the buildup of detritus as the main problem with sand beds. High flow and shallow probes with a gravel vac (export) seemed to be the solution from what I recall. I don't remember exactly, but I don't think they felt that the problem had anything to do with anaerobic portions of the substrate.

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Critical Fertilator: The Micromanager of Macronutrients

If it wasn't for the possibility of them burrowing directly into a pocket of gas, I wouldn't be worried. For the most part, anaerobic areas don't seem to be a big problem until disturbed.

It isn't the collection of mangroves that is the issue, it is possession. I'll double check, but I do believe it was a substantial fine. Pretty sure I can't import them either.

Are there any... well I suppose they'd be mangrove/bog type plants other than mangroves that could be used?

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

Indeed, my concern is the same as Callatya's. Anaerobic pockets aren't a problem until you open them up.

Certain salt marsh plants may be appropriate as plants, maybe?

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The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.

I'm still not convinced. I have/had a few burrowing creatures including a jawfish. He's changed his burrow twice I think in the time I've had him. Plenty of time for gas pockets to build up between moves. Could just be lucky but this is never a problem I've heard about people having with burrowing creatures in their DSBs.

If you check the species types that are covered by the law, american species might not be covered. They are different I believe. So you might be ok bringing in one of our red mangrove sprouts. Then again, I know how Aus is with watching for invasives, so maybe not.

Otherwise I'd go with macroalgaes. Feather caulerpa and others extend roots into the substrate, although not very far. You could probably even find and collect them somewhere.

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Critical Fertilator: The Micromanager of Macronutrients