STN RTN from Salt Alkalinity Swing

Potential down side to dosing vodka,vinegar and amino acids in a reef tank?

by Justin Hester

In previous articles, we have talked about the plus sides to dosing carbon sources like vodka and vinegar in our reef tanks, but is there a more elusive and dangerous down side we need to look out for?  Does the same apply for amino acid dosing? There just might be a scary corollary to dosing these supplements given the right or wrong bacteria culture living in your reef tank.  Again, we are not scientists here, but we are trying to pull together information from as many credible sources as we can find to learn about the complex bacterial systems that exist in our reef tanks.

Carbon and Amino Acid Dosing

Before we dive in, just what is carbon dosing and why do people add amino acids to their tank? Carbon dosing in its many forms can be broken down at a high level like this:  a carbon source is dosed into your reef tank at increasing amounts over a given time to grow a larger culture of certain bacteria.  These bacteria feed on nitrates and to a lesser degree phosphates.  So, increase the culture and the nitrates in your tank, and you will increase the nitrates that get fixed in the bodies of these little bacteria.  Next, your protein skimmer becomes the dominant means for exporting these nitrate-laden bacteria out of your reef system through your collection cup. For more on carbon dosing, check out our full articles here and here. Amino acids are typically added to enhance coral health, color, and growth in our reef tanks.  They act through enhancing the layer of photosynthetic algae that grow in the corals’ skin.  They can be especially helpful in low nutrient systems where corals can take on an almost pastel coloration.  This same effect has been documented by folks using non full-spectrum LED’s where only certain wavelengths of light are provided to the corals, thus reducing the diversity and quantity of algae growing in their tissues.

What potential hazards might be lurking at the microscopic level?

What if the addition of amino acids and/or carbon sources don’t only act as food for the nitrate consuming bacteria?  What if it also stokes the microbial fire in our tanks, launching blooms of detrimental bacteria that can cause coral diseases?  If this is the case, could our carbon dosing be creating a colony of Vibrio coralliilyticus or other bacteria known to negatively affect corals? Until recently, bacteria in general have always been thought to be free floating in the oceans, randomly landing on their hosts through sheer luck before affecting their damage. Some research has been done recently by Melissa Garren of MIT that is re-writing the book on how these “bad” bacteria can actually seek out and attack corals.  I have a hunch that this same process can run rampant in our reef aquariums given some of these high carbon and amino acid fueled environments we can potentially create. Here is a short video that illustrates how the bacteria move actively towards the corals.

Is this bacterial bloom the culprit for many an STN/RTN event?

We know that both in the oceans as well as in our reef tanks, both beneficial and detrimental bacteria exist.  What we are speculating on is what acts as the catalyst for them to explode in numbers and have detrimental effects on our corals.  Now that we know they can actually sense and move to corals, are they able to recognize when corals are weak?  Can they time their population expansion to occur when corals are signaling stress? Let’s take a look at coral anatomy, specifically branching corals like Acropora and Montipora. We know that the branches and tips of our corals serve a few purposes. First, they act as solar panels for the corals’ photosynthesis-driven energy production. Second, they also contain the main offense and defense mechanisms used to compete with other corals, algae, etc for this light. If you were a bacteria and we now know you can move where you like, would you settle in a highly defended healthy spot or would you exploit the easy-to-establish flank position that can be fortified and allow you to plan your larger attack?  When the bacteria settle at the base of these branches, I believe they are doing just this, exploiting a the weakest part of the coral, settle in to feed, and then replicate into an army that can then begin going after the more healthy tissues up the branches. To take this a step further, I speculate that when we hear reef hobbyists report of STN/RTN (slow/rapid tissue necrosis) occurring on certain corals, but not system wide, we might actually be seeing the bacteria work in this very manor.  Specifically, when we see corals losing tissue from the base or inside out, we are simply seeing these bacteria seek out the weakest coral and then the weakest spot in the coral. Observations have shown us that they attack from the center out on larger colonies rather than frags first. Wrapping this back into the carbon and amino acid dosing, my concern is that the conditions we can potentially create both increase the strength, color, and growth of our corals, but might also be fueling an army of these coral-consuming bacteria in the background.  Enter a trigger event like an alkalinity spike or drop, a pH swing, or some other stress and we may have our catalyst that can be just enough to initiate an STN/RTN event in your tank.

Can we mitigate or avoid this from happening?

This is a tricky question and I think there needs to be a lot more understanding about how these systems work in order to really draw some concrete conclusions here.  Some ideas I’ve had when I stare at my particular system and wonder how the mechanisms are working include the following: -Within the bacterial world of the oceans and our tanks, is there competition for resources that maybe keep good and bad bacteria populations in check.  Do these mechanisms work outside of the “add food and we will grow”  theory? -In our reef tanks, are there other things that we can do to make our corals more healthy and resistant to bacterial infections?  Are the lack of these things creating similar conditions to coral reefs that are bleaching in the wild due to bacteria like Vibrio coralliilyticus? -Do things like UV sterilizers help keep populations of bad bacteria in check?  If so, is it at the recommended 15000-30,000 uw/cm2 that we see to “kill bacteria” in a saltwater aquarium? -Why do these bacteria only attack certain coral species and even certain individuals in our tanks?  Is it due to their health, how potent their defenses are, or something else? -Is there a happy balance between growing coral strength and growing large bacteria cultures?  Perhaps better ways to alleviate nitrates like growing chaeto in a refugium? The answer to questions like these can only be flushed out through more science and observation regarding the microscopic relationships that are occurring in the oceans as well as in our reef tanks.  I would offer a word of caution to those hobbyists that are thinking about carbon dosing and or amino dosing.  Do so with keen observation over your systems. Look for the telltale signs of coral coloration changes, thinning of tissue, and any STN/RTN you might see at the center of your corals as this is more than likely the result of bacteria. Being in this hobby for almost 20 years now, I am still amazed at the cool and complex things we are still uncovering that occur right under our noses.  I do think that as reef hobbyists and mini scientists at heart, we offer an important real life lab to the scientific community.  The amount of eyes that we have literally inches from some of these intricate ecosystems offers us a level of “crowd observation” may someday play a vital role in coral reef science as more wild reef habitat’s dissapear every day.   References: Wired  05-12