Timothy Havonec cita uma competição entre bactérias autotróficas (nitrificantes – que usam dióxido de carbono) e heterotroficas, já que a primeira demora de 20 a 30 horas para multiplicar enquanto a segunda de 30 a 45 minutos e ambas competem pelo espaço
HUSBANDRY ISSUES
Given the capacity of these methodologies to drive dissolved nutrients to very low levels, unique issues arise of which the marine aquarist should be aware:
1. Maintain natural seawater parameters. It is important that abiotic water parameters are as close to natural levels as possible. The suggested levels are:
• Calcium 410–430 ppm
• Magnesium 1250–1300 ppm
• Alkalinity 6.5–7.5 dKH
• Potassium 380–400 ppm
• Salinity of 34–36 ppt
(Specific Gravity 1.024—1.026)
Perhaps the most important of these parameters is alkalinity. Many aquarists dosing organic carbon who have maintained consistent alkalinity levels above 8 dKH have reported varying degrees of tissue necrosis in scleractinian corals, especially corals in the genus Acropora, usually described as “burnt tips.” I have personally seen this effect, but the exact cause of this phenomenon is not known. Some suspect a phosphate deficiency. The prudent aquarist employing a probiotic methodology will pay close attention to alkalinity levels, especially as nutrients fall to nearly undetectable limits. Additionally, be aware that probiotic systems may cause a more rapid depletion of alkalinity levels than you may have seen in normal calcification processes.
2. Discontinue UV sterilization and ozone applications when using these systems. Almost all commercial probiotic systems recommend the discontinuance of UV sterilization and ozone on the basis that these applications will adversely impact the bacterial populations that the probiotic methodology is attempting to increase. With respect to UV sterilization, this reasoning may seem suspect, as the UV applications would not directly impact the biofilms and other benthic bacterial communities on the substrate. Nevertheless, ozone and UV applications are not recommended if employing a probiotic methodology, commercial or DIY.
3. Phosphate absorbers not recommended in some systems. The use of phosphate-binding agents, such as granular ferric oxide (GFO) is not recommended in some commercial systems. As an initial matter, many find it is unnecessary as some systems have the capability to reduce phosphate to very low levels. Additionally, there is concern that rapid depletion of phosphate caused by using GFO in conjunction with some probiotic systems may result in coral tissue necrosis, presumably caused by rapidly shifting the bacterial dynamics in the areas on or adjacent to the coral tissues. Many aquarists, however, do use GFO in conjunction with DIY carbon dosing applications and do not experience these problems. If continuing to use GFO, I suggest reducing the amounts and reactor flow rates, and observing the system inhabitants closely.
4. Use and maintain a good protein skimmer. A productive protein skimmer should be used in all probiotic methodologies. Foam fractionization removes some dead bacteria prior to decomposition, and may be a significant export pathway for the nutrients that have been “locked up” by the enhanced bacterial populations resulting from organic carbon dosing, although other important nutrient export pathways are involved, as discussed. Additionally, a protein skimmer adds an additional safeguard in the event of a bacterial bloom caused by an overdose of organic carbon. If your protein skimmer performance is marginal, consider upgrading before beginning a probiotic regimen.
5. Don’t overdose organic carbon. Although less common in commercial probiotic systems than in DIY applications, overdosing of organic carbon is certainly possible. Remember, these methodologies have the capability of causing significant shifts in the bacterial dynamics in the aquarium—in the water column, on the substrate, and on and in the tissues of coral. Excessively rapid nutrient depletion can cause stress in corals. In case of a substantial overdose, a bacterial “bloom,” or “whiteout,” can occur, usually presenting as a semi-opaque or milky white change to the water. The primary concern in this instance is oxygen depletion in the water column, caused by respiration by the bacteria cells. In most instances, the tank inhabitants will survive. However, a quality protein skimmer is the best defense against catastrophic oxygen depletion. The main caveat here is to go slow. Incremental increases in the dose and careful observation are the best safeguards.
6. Do your water changes. Many aquarists have cut down on the volume of water changed during periodic water changes, as water changes are no longer used as a means of significant nutrient export. Water changes are still recommended, however, in order to address certain mineral depletions, and for other reasons, such as reduction of allelopathic metabolites released by corals and other organisms. Once dissolved nutrients are reduced to target levels, at least a 5-10% weekly water volume change is recommended. It is particularly important to match the abiotic parameters of the change water to the aquarium water, given the potential problems associated with higher alkalinity levels in some instances.
7. Beware potassium depletion. In zeolite-based systems, significant potassium depletion may become an issue. Several explanations for this phenomenon may come into play, including those involving the role that potassium ions play in regulating pH gradients along cell membranes. Regular testing of potassium is therefore indicated when using these systems. Another reported indicator of potassium depletion is faded coloration in certain Acroporids, particularly Montipora capricornis. In the event of depressed potassium ion levels (below 370 ppm), a high quality potassium supplement is recommended.
8. Watch for nitrogen limitation. Almost all of the probiotic systems described are effective at reducing nitrate in the water column. Based on my observations, some are more effective than others at phosphate reduction. To a large extent, this effect is contingent upon the extant bacterial populations in the system and other chemical balances in the system. Nevertheless, the aquarist may encounter a nitrogen limitation issue, which may subsequently inhibit the rate of phosphate reduction. If nitrogen limitation is suspected, I recommend gradually increasing feedings, or institution of an amino acid supplementation program. This process requires a careful observation and a delicate balance, however, as rapid increases in food wastes and other sources of dissolved nutrients can overwhelm the system, especially initially.
9. Maintaining sand beds and algal filters. Most zeolite-based commercial systems suggest a shallow sand bed to increase the available substrate for biofilm development. Some users with deep sand beds have reported difficulty in obtaining consistent dissolved nutrient reduction when transitioning into a probiotic system, for reasons yet to be conclusively determined. Likewise, the aquarist may experience a long-term inability to maintain macroalgae-based filtration methods due to the lack of nutrients available to the algae. If the dosages are carefully balanced, however, it is possible to keep macroalgae alive, and sustaining some growth, although the balancing will have to be relatively precise.
10. Managing smaller systems. I have used various probiotic systems, including ZEOvit, in aquaria as small as 20 gallons. In my experience, a “balanced” microbial biology is more difficult to achieve with a probiotic methodology in smaller (less than 50-gallon) systems, presumably due to a more limited amount of substrate available for biofilm development. Nonetheless, the benefits of probiotic methodology can be achieved in smaller systems with patience and careful observation. On a related note, I have found that a mixed-source DIY application (utilizing vodka, glucose and vinegar), along with periodic bacterial inoculations, gave the best, and most stable results in smaller reef aquaria, although the pelletized polymers certainly appear to be amenable to this type of application as well.
CRITICISMS OF PROBIOTICS
There is considerable scientific support for the conclusion that excess dissolved organic carbon may be associated with coral mortality on natural reefs. The amount of dissolved organic carbon that constitutes a dangerous level in a reef aquarium has not been determined.
Additionally, a common criticism of probiotic methodologies is that some pathogenic bacteria are heterotrophic. In order words, organic carbon dosing feeds the “bad” bacteria along with the “good” bacteria. There appear to be few, if any studies that suggest that pathogenic bacteria are more efficient than desirable species in the ability to uptake dissolved organic carbon. If the aquarist proceeds slowly and incrementally, the risk of coral mortality appears low.
These methodologies are also criticized as being “unnatural.” The fact that we pull marine organisms off a reef and stick them in a glass box with artificial seawater makes that entire philosophical discussion pointless in my view. The real issue is what we can do to create a captive environment that maximizes the health of the inhabitants.
Certainly, excess nutrient levels and the problems associated with them—algal overgrowth of corals, inhibition of calcification due to elevated phosphate levels, and proliferation of pest organisms, among other things—are not “natural.” Conventional wisdom often supposes that other husbandry practices, such as algal filters and related filtration techniques, are more “natural,” and hence more effective, than the active management of bacterial populations that probiotic systems foster.
That supposition is, unfortunately, misplaced.
Communities of bacteria, archaea, protists, and unicellular fungi account for most of the oceanic biomass. These organisms may be responsible for as much as 98 percent of primary production, and mediate all biogeochemical cycles in the oceans to a significant extent. On a “natural” coral reef, to use the term broadly, bacterial communities are responsible for most of the nutrient cycling, more than algal communities, not only as a result of having more biomass, but also because heterotrophic bacteria are potentially more efficient nutrient scavengers than algae due to their small size and large surface-to-volume ratio, among other factors.
The conventional “more natural is better” paradigm is therefore turned on its head.
Finally, the average hobbyist spends significant time and money in creating the best obtainable environment for his or her macroorganisms. The same effort and investment should also be directed to the most important organisms in the aquaria—the bacteria and the biofilms they build and populate.
CONCLUSION
Probiotic methodologies are not for everyone, and are not without risks. They generally require careful monitoring of abiotic parameters, and, in the case of some commercial systems at least, can be considered somewhat expensive. However, with a slow and incremental approach, and careful husbandry, these systems are an extremely effective means of controlling dissolved nutrient levels in the marine aquarium.
Murray Camp is a trial lawyer and marine aquarist with more than 15 years’ experience in reefkeeping. He speaks frequently at aquarium society events and lives in Dallas, Texas.
muito obrigado pela atenção de todos 