(First of all I'm sincerely glad you asked these questions cause this is the central topic of my PhD research I'm defending on Monday and this is sooooo much help finishing the report writeup)
This statement is misleading. It's statements like this that lead hobbyists to believe that worms are reducing their nitrate and phosphate level by locking them up in biomass. That is simply false. It is irrelevant if one worm is locking up these nutrients in biomass, when the worm next to it is decomposing and releasing all its stored nutrients back into the environment. Like I said. It is the population that matters. You will not get a reduction of nitrate and phosphate with a stable population of worms.
First of all, you're largely right, but there's one thing I would argue [and which I try to defend in the proposals I'm working on] is important: the worms stir up phosphate deposits (organic, mineral-bound, what have you), which shifts around its redox states and changes their solubility to change which can help return it to the water column to be removed by filtration. Again though, you're right that it's not the worms eating stuff that reduces phosphate, it's the fact that they're there stirring stuff.
How is any of this beneficial to a reef tank? Allowing organic matter to accumulate in a sand bed, then having worms move it, along with oxygen, deeper into the sand bed, simply increases the area, and speed of decomposition. Decomposition is not beneficial to a reef tank.
Actually, decomposition is a good thing, but we want only certain kinds of decomposition. Decomposition (ie breakdown of organic matter) takes place in a certain order: aerobic degradation takes place first until oxygen is depleted, and this produces ammonium as a result, which is oxidized to nitrate. This nitrate can have one of two fates: it can be used by our higher life like algal cells (including non-pest bacterial plankton), most corals, and other cellular plankton that form the base of the food chain. HOWEVER, most of the nitrate goes through the other pathway if things are operating properly (which is good, because we don't want too much flowing to the organisms and becoming pest algae floods): denitrification, which replaces oxygen as the electron acceptor to degrade organic matter after oxygen is depleted. The catch is that if there isn't enough organic matter left over (which would require at least 150 micro moles/L...a significant amount), then there will be nothing to fuel denitrification (which requires both organic matter and nitrate). If there's nothing stirring the surface and/or not enough free organic matter, then oxygen never gets used up and nitrate never gets reduced to free nitrogen. Why not just reduce the organic matter and cut off the nitrates that way? You can do that if it suits you, but be warned that all reef tanks with corals need some form of feeding. If you prefer to control the feeding yourself, then whatever method suits you...this is off topic, though.
Solid particles of organic matter are loaded with harmful nutrients.
nitrate and phosphate are not harmful (except at VERY high concentrations. They do, however, fuel growth: both the growth of our corals and reef, or algae if we don't properly manage nutrient levels with proper denitrification.
If we remove these particles, before they decompose, the nutrients they contain can not degrade our water quality. The nutrients contained in a solid particle can only degrade our water quality, after that particle has decomposed, or as it decomposes. Worms, pods, and all the other little magic critters simply aid in the decomposition process. They are part of the problem. Not the solution.
Except that it isn't a problem, as I hope I've shown. I really do hope that's clear. It's a complex topic, but I cannot stress enough that there is solid science that supports everything I said, including my own research which is in preparation for the Journal of Exmperimental Marine Biology and Ecology. Nutrients are NOT a problem unless they are in excess or depletion. The trick is a balance to get it in the sweet spot.
How is it even possible? "Biodiversity" is such a cool sounding term, that everyone thinks we must have it. Until you stop and think about what it really means. When we stock a tank, we introduce a huge diversity of organisms from many different environments around the globe. In time, some of these organisms will die off while other prosper. Those that are well suited to the conditions of our system, prosper. Those that are not, don't. We don't need a diversity of organisms. We need organisms that are well suited to our system. Nature takes care of this for us. Adding diversity, for diversities sake, simply causes more organisms to die, rot, and degrade our water quality.
It's possible because every study
in the field (ie. nothing yet has been done directly for the tank, which is the research I'm working on) of benthic biodiversity (ie. the number of species or functional groups) has shown that it supports increased ecosystem function, defined as the ability to support new biomass (including coral growth), as well as denitrification, which we want to limit the supply of nitrate to reasonable levels and prevent algae overgrowth. Supporting that diversity is merely a matter of ensuring there is enough net nutrient flow to support it from the get-go; there are strong links in ecology between energy/nutrient flow and biodiversity. in the ideal case, you should never have to add diversity (though if you don't, it may cause OTC, as below). However, the original question was whether to remove the worms, and I hope I've made the case that we should keep them. [I hope very much I've made my case, because the plans for the rest of my life as well as the past decade's justification depends on that case, though in more detail] Now, all we can say now is that biodiversity dupports ecosystem function...I'm working on why that's the case and have a theory in the works (in prep for a paper), but we don't have a proven explanation yet.
IMHO, the cause of OTS is pretty obvious. It's the accumulation of rotting organic matter. I've never seen, or heard of, a clean tank suffering OTS. I've only seen it in tanks that have been neglected. The method of maintaining the typical "DSB" requires that you neglect the tank. Which is why OTS is such a common problem with DSB systems. This is just my opinion though.
I would say you're largely right in principle, but I would argue that loss of diversity causes denitrification to shut down and nitrates to accumulate to unsafe levels. You also lose the cycling of phosphates, which allows for dangerous buildups as well. Though this is only "true" OTS..many cases os so called OTS are, we seem to agree, cases of neglect.
So in other words, a sand bed does absolutely nothing to reduce phosphate.
As explained above, it has to do with helping it back into solution, where it may be complexed and removed by filtration.
In fact it is a phosphate factory on the bottom of the tank. It takes harmless solid particles containing phosphate, breaks them down, and releases that phosphate back into the system where it can fuel algae growth, and cause health, and growth problems for stony corals.
It's really the same case as with nitrates (though without the endgame of denitrification). But do remember that it's possible to remove dissolved phosphates, as well as organic-complexed phosphates, fairly easily. So having the mixing helps flush the phosphates out of the bed into the water where it can be removed by the filters. It can also be removed, of course, by corals, and do remember phosphate is necessary for growth. It can cause harm in high concentrations, but is still needed in low ones, much like nitrate. And to anticipate a potential question: why not let the phosphate stay locked up in the particles? It won't...those particles WILL be broken down if they are organic, and there is no way to prevent it in an aquarium. Mixing prevents buildup of phosphate.
I still don't see the benefit.
I hope by now that you do, though I will also add that I am not claiming it's impossible to support a reef without these. They're beneficial, though, and they can play a central part of a successful sand bed method.
And yes, I'm biased because I've spent the past 104 weeks (literally, no time off...) studying these guys. Do feel free to ask questions (though if you want citations, it must wait until I'm back on my work computer tomorrow)...I gotta be able to explain this!
Cheers!
