Quote:
Originally Posted by elegance coral
These systems are growing more and more nutrient rich. They're being flooded with allelopathic substances.
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This is absolute rubbish. Nutrients are recycled as food & removed from the water via filtration & water changes. They are not just left there to build up & up. Your assertion is ridiculous. If this was the case we couldn’t feed the inhabitants at all.
Allelopathy is the new argument against algae filtration, but is used in a misleading way.
External forces can create conditions that enable increases in the mass of, and area taken up by, algae species already existing on healthy natural reefs. Healthy natural reefs do have, & need algae to function. But, if the algae’s mass increases significantly this can create conditions that are favourable to algae & detrimental to corals. It is precisely this increase in algae biomass, going out of balance within the system that is the problem, not the algae per se. It’s akin to adding a bag of sugar to a sauce recipe recommending a teaspoon.
All photosynthesising organisms produce sugars. As I understand it, a few of these sugars specifically are utilised by virulent bacteria in particular. Not all photosynthesising organisms produce these specific sugars, but some species of algae, & even some species of zooxanthellae found in corals do. The algae’s that do produce these specific sugars typically produce them in higher percentages within their exudates, & in larger volumes than coral zooxanthellae do. But, on healthy natural reefs this is not a problem as these sugars, & even virulent bacteria all play a role in keeping a reef healthy, as does the algae itself.
But, if the mass of these particular algae species increases significantly, due to circumstances such as an influx of nutrient run off from land, or where over fishing or disease has significantly reduced the population of algae grazing fish & invertebrates, the volume of these sugars produced also increases & this can in turn increase the population of virulent bacteria, & this increased virulent bacteria population can be detrimental to corals.
An aquarium utilising algae as a filtration method cannot be regarded as analogous to an unhealthy reef as described above, but is analogous to a healthy reef.
In regards to nutrient run off from land, the primary purpose of growing algae as a filter method is too reduce nutrients, as happens in nature. So, the nutrient runoff into your aquarium is you feeding the inhabitants. The filtering algae’s function is to remove the resulting inorganic nutrients so they do not build up in the system.
The act of harvesting the filtering algae as it grows replicates the function of grazing fish and invertebrates, limiting the algae biomass within the system at any given time.
So, the algae used as a filter does not continuously increase in volume like it does on an unhealthy reef, but is controlled like it is on a healthy reef.
One of the direct consequences of an increase in algae biomass on reefs that is most detrimental to coral health is the fact that algae live in and among the corals & start to physically touch the corals. It is this proximity and physical contact, specifically, that is a problem.
When using an algae scrubber, chaeto reactor or chaeto refugium the filtering algae is segregated within its own housing, typically separate from the display tank, and this physical contact scenario is taken out of the equation.
Some argue that the spores from the filtering algae can find their way into the display tank and take off, colonising the display. This has never happened in my case, using an algae scrubber. Even putting the screen full of algae into the display to feed the fish has not resulted in it taking up residence. More telling is the fact that the algae that naturally began growing on my screen, a species of ulva, was obviously already in the system to begin with. The scrubber not only provides a perfect environment for the ulva to prosper when it hadn’t otherwise, it inhibits algae from growing in the display, as indicated by the fact that other algae species, and cyano species that were growing in my display, prior to installing the scrubber, totally disappeared afterwards & never reappeared.
Using recorded incidences of coral mortality, via allelopathy on natural coral reefs negatively affected by external forces, to argue against the use of algae as a method of nutrient reduction in aquaria, is mischievous in my opinion.