Insufficient nutrition for hermit crabs?

[robg]

Okay, so it's coming up two months since I set up my Kent Marine 94 L BioReef system. I intended to post more about it over the last few weeks, but life has been busier than expected. So it goes.

I had a scooter blenny that seemed to be quite happy for a few weeks, then became inactive and died within a couple of days. (This will be the subject of a separate post.) But the death of this fish got me thinking about another issue I have experienced, involving hermit crabs.

When I set up my aquarium, the first thing I added was a cleanup crew consisting of one cleaner shrimp, four scarlet-legged hermits, and a number of snails. At the time, I asked the guy at the LFS (who seems very knowledgeable and helpful) whether I needed to add anything special for the crabs to eat. He assured me that they would find plenty to eat on the live rock, and I didn't need to worry about it.

The short version of events is that over the past few weeks, three out of the four hermits have died. The fourth one is still alive, but has become less and less active. So I'm wondering… is it possible that there just isn't enough nutrition in the tank to sustain them? And if not, is there anything I can add to the tank to provide them with adequate nutrition? (P.S. Shrimp and snails seem to be OK.)

 

[SteveAnem]

You could always throw in a few of those algae or marine pellets that sink to the bottom if you're worried?

 

[Bluez_01]

It really annoys me when LFS say "You dont need to feed CUC on a new start up", If anyone should ever get this reply again, ask the LFS so what exactly is the crabs/shrimps etc.. going to eat, rock? sand? (Both of which will be pretty much spotless if its new, and if its gone through a cycle which it will probably would have, then anything worth eating will be dead or rotted, or worse still full of ammonia locked up in it) unless your rock is covered in algae when you first get it and even then the crab isn`t really going to be interested in it until its almost starved to death, there is nothing in a new tank for it/them to eat, crabs eat algae for one reason mainly, thats to eat the nutrient within it (aka, bits of food, fish waste, etc...) on a new tank none of this will exist, so the crab/CUC starve, the only rule to the exception are snails, which will took in to everything and anything they come across.

This is not a rant at you personally, but I do wish that some LFS`s use there loafs a bit and ask questions, most LFS`s will ask the question about what type of rock/sand it is (cured/new), and how long has it been running, many will suggest the same thing I am going to suggest to you, which is buy some frozen prawn/shrimp (cooked or uncooked doesn`t matter) and throw a few small bits (2-3) every couple of days until you feel that there is enough food/detritus laying around on the sand bed, under the rocks etc... that the fish don`t show any interest in after they have been fed, only then you can safely know for sure that your CUC are getting fed at the early stages, once the tank matures, then you can feed the prawn/shrimp as a treat every so often, reduce the feeding on the fish back so very little ends up as a waste, the fish will scavenge around the rocks to find bits of food if they are still hungry.

HTH.

 

[robg]

Thanks much for your comment, Bluez_01.

Buy some frozen prawn/shrimp (cooked or uncooked doesn`t matter) and throw a few small bits (2-3) every couple of days until you feel that there is enough food/detritus laying around on the sand bed, under the rocks etc... that the fish don`t show any interest in after they have been fed, only then you can safely know for sure that your CUC are getting fed at the early stages, once the tank matures, then you can feed the prawn/shrimp as a treat every so often, reduce the feeding on the fish back so very little ends up as a waste, the fish will scavenge around the rocks to find bits of food if they are still hungry.

So, given that my tank is now reasonably well established (2 months; consistently no ammonia or nitrites; decent amount of green algae on rocks), would you still recommend throwing in some prawn/shrimp? If so, is this something I should be buying from the LFS, or should I just buy a bag of frozen shrimp from the supermarket?

 

[Bluez_01]

Supermarket nothing fancy just cheapest you can get really, I would say that a self containing CUC would be around the 4-6 month mark, unless you are feeding heavy on the fish side, I still feed once a week on my tank and thats coming up to 4-5 months, although I do run a ULNS so I am mindful of that as well.

 

[robg]

Supermarket nothing fancy just cheapest you can get really, I would say that a self containing CUC would be around the 4-6 month mark, unless you are feeding heavy on the fish side, I still feed once a week on my tank and thats coming up to 4-5 months, although I do run a ULNS so I am mindful of that as well.

OK, thanks. I do deliberately overfeed a little on the fish side in hopes of leaving some for the CUC, but given crab deaths this would not seem to be sufficient.

Will the fish population not eat the bits of shrimp/prawn?

 

[Ishy]

Thanks much for your comment, Bluez_01.



So, given that my tank is now reasonably well established (2 months; consistently no ammonia or nitrites; decent amount of green algae on rocks), would you still recommend throwing in some prawn/shrimp? If so, is this something I should be buying from the LFS, or should I just buy a bag of frozen shrimp from the supermarket?

The first thing my hermits did when I put them in was to completely strip the Algae from every rock so its strange you say you have plenty. The other thing was that 3 of them up graded to larger shells, one on the first day and two a few days later so it may be an idea to have some different empty shells in the tank.
The one that changed shell on the first day tucked himself into a hole in the rock soon after he changed shell and looked dead, we left him alone thankfully as it turned out he was moulting and took about 3 days.

 

[doug_amanda]

I would be surprised if starvation is the problem, unless you rock is bleached white and virtually sterile I think most crabs will find enough food, particularly in a tank with fish. I could be wrong but My first thoughts after reading your post was possible ph swings. Would be worth doing a test just before lights out and again just before the lights come on.

 

[robg]

The first thing my hermits did when I put them in was to completely strip the Algae from every rock so its strange you say you have plenty. The other thing was that 3 of them up graded to larger shells, one on the first day and two a few days later so it may be an idea to have some different empty shells in the tank.

Well, I'm no expert but there certain seems to be plenty of algae – lots of green coloration on both my LR and my plain ocean rock.

The one that changed shell on the first day tucked himself into a hole in the rock soon after he changed shell and looked dead, we left him alone thankfully as it turned out he was moulting and took about 3 days.

I've made sure there is a selection of empty shells of various sizes, but none of them have shown any interest and I haven't seen any of them moult in the two months I've had them.

Sadly, by Saturday morning the one remaining crab was dead. The guy at the LFS just said "Oh well, you have to replenish crabs quite often, especially in the first few months."

 

[robg]

I would be surprised if starvation is the problem, unless you rock is bleached white and virtually sterile I think most crabs will find enough food, particularly in a tank with fish. I could be wrong but My first thoughts after reading your post was possible ph swings. Would be worth doing a test just before lights out and again just before the lights come on.

As I just said to another commenter, I'm no expert but there certain seems to be plenty of algae – lots of green coloration on both my LR and my plain ocean rock. So perhaps lack of food isn't the problem after all.

I've done a number of pH tests over the past few weeks and it always reads around 7.9. But I've never done consecutive tests just before lights out and lights on. Why would the pH vary during these periods?

 

[eddyc]

Ph varies because while the lights are on the algae produces oxygen & uses carbon dioxide and while the lights are off it uses some of that back up and produces carbon dioxide just like plants so the higher levels of carbon dioxide lowers the ph when lights are off. Thats one of the reasons people use an algae bed in the sump reverse lit to help counteract that ph drop.

 

[eddyc]

Also have you checked after lights out for any hitchhikers that may be killing the crabs. In my laat tank i took 8 teddie bear crabs out in 9months using a bottle trap. It may be an idea to make one from an old coke bottle and bait it with a bit of food and see whats in there in the morning.
They are easy made just cut the bottle just before it starts to narrow and turn the neck around and push it into the other half, mind to take the label off too.

 

[robg]

Ph varies because while the lights are on the algae produces oxygen & uses carbon dioxide and while the lights are off it uses some of that back up and produces carbon dioxide just like plants so the higher levels of carbon dioxide lowers the ph when lights are off. Thats one of the reasons people use an algae bed in the sump reverse lit to help counteract that ph drop.

OK, thanks for the info. I'll check it out.

 

[robg]

Also have you checked after lights out for any hitchhikers that may be killing the crabs. In my laat tank i took 8 teddie bear crabs out in 9months using a bottle trap. It may be an idea to make one from an old coke bottle and bait it with a bit of food and see whats in there in the morning.

Where would such things as teddy bear crabs be coming from? I haven't seen any evidence of any creatures in the tank other than the ones I've put in myself.

 

[eddyc]

They bury into holes in the rock

 

[eddyc]

Theres also other things like pistol shrimps and mantis shrimps

 

[robg]

EddyC: OK, thanks. I know there are sometimes things hidden in the LR, but after two months I haven't seen any sign of anything.

 

[eddyc]

After 9months i found a crab in my curent tank

 

[robg]

After 9months i found a crab in my curent tank

Ah, OK…

 

[CEECH]

I found a gorilla crab in mine that killed my dwarf hermits. Are you sure if you added the CUC so soon part of the cycle may have damaged and killed them. I always feed extra for my CUC so they have food also. Minute food hits the water snails are out and seaserpant star.