Derasa Clam causes coral bleaching due to chronic low nitrate

[acropora1981]

So I have a little theory here.

I have had about 20 or so SPS corals that I've had in a 28g jbj nano-cube for about 2.5 years. About 2 years ago I was given a Derasa clam from a friends tear-down. It was abour 3" long at that time. About a year later, 1.5 years ago it had grown to about 4 or 5" and at that time all my sps stopped growing and began slowly bleaching. No cause was ever pinpointed, and I tried many things. The only thing that ever partially reversed the bleaching process was to add small amounts of potassium nitrate daily for many weeks. Nitrate was undectable using seachem's fairly sensitive nitrate test.

I recently sold the clam, as it had reached >6" and was not very comfortable in the tank any longer. VOILA! Corals are coming back from 1.5 yrs of bleaching.

Can it be that the clam was taking out so much nitrate as to starve out the zooxanthellae of my SPS corals? It is the only thing that makes sense to me. I've been keeping SPS for 15 yrs and I had never had this problem before, nor was there any temperature swings as I run an RKL and the tank is always around 80F. KH and calcium are stable using kalkwasser and a small calcium reactor. As far as I could tell, phosphate never up over 0.1 on a hanna meter, and usually never more than 0.05

Anyone heard of this before? Nitrate is now at <1 ppm, but it shows as a very pale pink in the test solution, instead of a completely colorless reaction that has been the norm for the last 1.5 or so yrs.... call me stupid, but did I bleach my corals with an oversized clam?

 

[chrisqueenz]

Interesting, I shall be following as I think I might be in a similiar situation

 

[chrisv]

I dont mind your theory. I rely on clams as an integral part of my filtration.

 

[A.G]

Iam in the same boat as you . I did this expiremant, I had a beautifull green monti cap that had very deep green color originally and placed it in my tank. It start losing color to very light light pale greenish white. I thought it was dying so I fraged it and gave to a friend who had a FOWLR but had MH on his tank and I realy did not want to lost the monti. few months later his frag turn into a colony bigger than what we originaly bought ! and mine has lost all its green but still survive. My NO3 0 and his is about 10-15. I tryed and gave him another acro frag that lost all its blue and guess what I could not believe when I saw it. Both tanks run with RO3 MH 150w Phoienx. But his tank is little dirty.No water change , feeding like crazy ..I have already lost corals that went very very light color.

I started feeding alot alot ALOT more and made my skimmer on very dry mode. Will see if this would work.HTH

 

[TheFishTeen]

We keep a very large (18"+) Derasa clam in our 800 Gallon Display at the LFS i work at, and have no problem keeping SPS. But that could be that its in a system with other 1500 Gallons.

 

[acropora1981]

Seems like some others have similar experiences. As for the 800 gallons - im sure that has many fish. My tanks run very very (obviously overly) clean and are very small (30ish gallons). Anyway, corals have continued to improve polyp extension and coloration as nitrate is now present to feed zooxenthellae. I just thought it would be a good post - now when people mention putting a larger clam species in a small tank, there is another reason why it may be a bad idea! Not just for the clam, but for the corals that it out-competes for waste! Obviously its just a theory, and would need some imperical tests.

Makes me wonder if clam fields in the wild can out-compete corals using the same strategy, in order to monopolize space on the reef. I actually imagine they don't; theres too much turn over.

 

[chrisv]

I feel like the super huge clams that some LFS have in tanks plumbed into their main systems are an integral part of filtration. like one giant aquatic kidney. My LFS has a large gigas and that guys husbandry is not very good. I think it is the reason he maintains low levels.

 

[thebanker]

What do tridacnid clams actually eat? I thought they subsisted on their own photosynthetic symbionts, and ate phyto and suspended microalgae in the water column.

Or is it more complicated than that?

 

[chrisv]

It is more complicated than that. They have the capacity to pull nitrogenous waste and by some (fewer) accounts phosphates directly from the water. Read Fatherree's clam book for the details on this.

Commercial clam aquaculture facilities actually add ammonium nitrate to the water.

 

[acropora1981]

What do tridacnid clams actually eat? I thought they subsisted on their own photosynthetic symbionts, and ate phyto and suspended microalgae in the water column.

Or is it more complicated than that?

Remember, its not just what the clam takes in, its what the clams zooxanthellae symbionts need as well. All algae require nitrate and phosphate to thrive. Including symbiotic algae.

 

[multicincta]

Sorry if this is hijacking:

So am I to understand that both SPS and clams need nitrate? My nitrate stays right around 20ppm and I've been trying like crazy to get it down. Should I simply not worry about it? Everything else is check. As noted above, I knew that they had a symbiotic relationship with algae. I just hadn't put together how important the need for nitrate was for both.

 

[elegance coral]

A clam is not going to have a huge impact on the nitrate level of the system. Nitrogen is an element. Elements can not be destroyed under normal conditions, so the clam is not destroying it. The clam never leaves the tank, so it doesn't remove it. As the clam grows, it will hold more and more nitrogen, but this isn't going to be enough to have a huge impact on the system. If the system isn't being fed, the water is changed regularly, and it's kept clean, the inhabitants can suffer malnutrition. Nitrogen deficiency may be part of this. Typically, in such a case, it will be the larger animals that suffer first. They are the ones with the highest demand for nutrients like nitrogen. So...... If you had a nitrate deficiency, that was effecting your pets, it would most likely show itself in the clam, long before you saw it in your SPS.

 

[acropora1981]

A clam is not going to have a huge impact on the nitrate level of the system. Nitrogen is an element. Elements can not be destroyed under normal conditions, so the clam is not destroying it. The clam never leaves the tank, so it doesn't remove it. As the clam grows, it will hold more and more nitrogen, but this isn't going to be enough to have a huge impact on the system. If the system isn't being fed, the water is changed regularly, and it's kept clean, the inhabitants can suffer malnutrition. Nitrogen deficiency may be part of this. Typically, in such a case, it will be the larger animals that suffer first. They are the ones with the highest demand for nutrients like nitrogen. So...... If you had a nitrate deficiency, that was effecting your pets, it would most likely show itself in the clam, long before you saw it in your SPS.

Well it didn't manifest in the clams. Unless you have figures to back it up I'd say you've jumped the gun here. A 6" Derasa is possibly going to have a significant impact on the nitrogen levels in a tank 28g in size(small tank, large clam). I think the clam is probably a lot better at monopolizing nitrates than corals, starving them out.

 

[mc-cro]

FWIW, I have a 18"+ derasa, and I have had in systems as large as 400g, and for the last 6 months he has been in a temporary system of less than a 100g. I see no impact to my sps, such as bleaching.

 

[thebanker]

What does a clam do, chemically, with NO3? The only thing I can imagine it does is use NO3 to manufacture more zooxanthellae as it grows... but that's about it. And they don't grow fast enough to be an efficient exporter.

If they really did filter nitrates, wouldn't more people be saying "nitrate issues? simply add clams to your system" instead of "add a refugium"?

I'm with elegance coral on this one.

 

[chrisv]

A clam is not going to have a huge impact on the nitrate level of the system. Nitrogen is an element. Elements can not be destroyed under normal conditions, so the clam is not destroying it.

You're right! It's not destroying it. It's metabolizing it. The nitrates CAN be metabolized into plenty of other compounds. If nitrogenous compounds are bound in the tissue of the clam, they are in effect removed from the tank until the clam either returns them to the water via excretion or by dying when someone tries to keep a 6 inch clam in a 30 gallon tank.

Nitrate does not equal nitrogen.

Help yourself to a biochemistry textbook, sir.

Nitrogen is the fourth most common element in living organisms. It is present in many, many macromolecules (like DNA, RNA and proteins) as well as in many smaller molecules (ammonia, nitrite and nitrate).

I assure you that a clam this large in a tank this small is a kidney. It will strip nitrogenous waste from the water (and you will probably never maintain calcium and alkalinity unless you're dosing like crazy and doing a ton of water changes).

 

[elegance coral]

You're right! It's not destroying it. It's metabolizing it. The nitrates CAN be metabolized into plenty of other compounds.

There is a huge difference between "metabolizing" something, and making it go away. The nitrogen is still in the system. "Metabolized", or not. Nitrogen cycles through our systems very quickly.

If nitrogenous compounds are bound in the tissue of the clam, they are in effect removed from the tank until the clam either returns them to the water via excretion or by dying when someone tries to keep a 6 inch clam in a 30 gallon tank.

It is the growth rate of the clam that locks up nitrogen. In no other way does a clam reduce nitrogen from the water. In order to fuel that growth rate, you must maintain a given amount of nitrogen in the system. If the nitrogen level drops, the growth rate drops, and the clam locks up less nitrogen. If the nitrogen level drops to low, the growth rate will stop, and the clam will die. What you're insinuating, is that the clam will continue to grow and lock up large quantities of nitrogen, even after the level in the system has dropped low enough to adversely effect SPS corals. That's not going to happen. The vast majority of SPS corals have evolved to thrive in very nutrient poor waters. The clam will be adversely effected by a nitrogen deficiency, long before most SPS corals are.

Nitrate does not equal nitrogen.

Help yourself to a biochemistry textbook, sir.

LOL. How about you go find a link to show us that we can have nitrate without nitrogen. As long as nitrogen remains in the system, the potential for it to find its way back to nitrate will remain. Why must I list all the possible compounds that contain nitrogen? Shouldn't it be sufficient to simply use the word, nitrogen? Even if you could magically remove all the nitrate from the system, it really wouldn't matter much, because all the nitrogen bound in ammonium and nitrite, will soon be more nitrate. It is the nitrogen level that's important. Not the nitrate level. The nitrate level only accounts for a portion of the nitrogen in the system.

I assure you that a clam this large in a tank this small is a kidney.

No, it is not. A kidney concentrates nitrogen and passes it to the bladder for removal. A clam does not aid in the removal of nitrogen. It simply traps a small portion as it grows. There is a huge difference between removal of a substance, and trapping it in the system. If our kidneys simply trapped nitrogen, like a clam, we would die.

 

[acropora1981]

What sticks in my mind here is the difference in bio-mass between SPS and clams. The clam has a relatively huge amount of living tissue to feed relative to SPS which is essentially mostly calcium carbonate with a thin living skin. I would postulate that one derasa clam would have maybe 10x the amount of living tissue as the rest of the SPS in the tank. Thus monopolizing, and trapping, most of the nitrate entering the system is conceivable. I agree that the clam would excrete much of what it had taken up, but that also a large amount would be incorporated into proteins in the clams growing tissues.

I think to answer how much nitrate a clam would and could sequester we would need empirical data from a study. Here's a good start
http://www.mendeley.com/research/nu...equirements-for-tissue-growth-and-metabolism/ That study states that nearly 100% of excreted nitrogenous wastes from the host are re-absorbed by the zooxanthellae.

Certainly under-feeding was a factor here, but I beleive the large clam furthered the effect.

 

[elegance coral]

What sticks in my mind here is the difference in bio-mass between SPS and clams. The clam has a relatively huge amount of living tissue to feed relative to SPS which is essentially mostly calcium carbonate with a thin living skin. I would postulate that one derasa clam would have maybe 10x the amount of living tissue as the rest of the SPS in the tank.

Lets assume that you are correct. What this means, is that the clam will require much more nitrogen than the SPS corals. If the nitrogen level drops, who's going to suffer first? It will be the clam.
As an example. Take an elephant, and a goat. Start out feeding them the same amount of food. Every day, reduce the amount of food evenly. Which animal will suffer malnutrition first? It will be the elephant. The goat will still have a surplus of food, while the elephant is starving. The elephant requires much more nutrition to maintain its biomass than the goat does, therefore, it will suffer first. In the scenario you describe, the clam with its greater biomass, will suffer before the SPS corals with their smaller biomass, when nutrients are limited.

Thus monopolizing, and trapping, most of the nitrate entering the system is conceivable.

I agree, given our scenario, that the clam would uptake more nitrogen than the SPS corals. The elephant, I spoke of, would consume much more than the goat, but it would still starve, while the goat was fat and happy.

I agree that the clam would excrete much of what it had taken up, but that also a large amount would be incorporated into proteins in the clams growing tissues.

The clam would require much more nitrogen, to incorporate into proteins, to produce the growing tissues, than the SPS corals require. When the nitrogen level in the water declines, it is those with the greatest demand for nitrogen that will suffer first.

That study states that nearly 100% of excreted nitrogenous wastes from the host are re-absorbed by the zooxanthellae.

That would become virtually irrelevant, once the clam started discharging zooxanthellae. A process that continues throughout the life of the clam. As the zooxanthellae grow and reproduce, the clam must periodically discharge a portion to allow for more zooxanthellae growth and reproduction. The discharged zooxanthellae take the nitrogen, they absorbed from the clam, with them when they are discharged.

Certainly under-feeding was a factor here, but I beleive the large clam furthered the effect.

It's hard to say why your SPS corals were bleaching. They can be very sensitive animals, and bleach for many different reasons. Reasons that we are still trying to fully understand. I highly doubt it had anything to do with a nitrogen shortage, if you had a large clam that was growing and doing fine.

 

[RoWall]

I was wondering about the similarity of this situation with the one when you have a lot of green thread algae in the process of aquarium maturation.
They continue to grow, while you measure 0 NO3 and 0 PO4 in the system. They simply take up all the available NO3 from the system, as fast as it's produced. Somehow, they do i faster then other algae and organisms in the aquarium (at least for some time).
Maybe the clam is more efficient then sps in taking up the NO3?
Maybe that's because it relys on NO3 much more then sps do in their natural environment?
Just my thoughts.