Hi again, Charles:
>>Incidentally, the question isn't academic with respect to keeping tanks. Steve Tyree talks about environmental gradient tanks in his book, Sea Squirt and Sponge Filtration Techniques.<<
I've been avoiding saying this, but feel I must at this point - and gave it some serious thought in prior posts. Steve is an accomplished aquarist. When you have kept corals and reef tanks for awhile, you get pretty good at the whole thing, and to be honest, its rather hard not to be successful so familiar are you with the needs of the animals. Steve, like Mike Paletta, and some others, have done a virtual 180 in terms of what they "promote" these days. These are the old -school hard core haevy skimmer use folks of yesterday that finally realized that running tanks with more food in the water column gave them better results - be it mud, sponge filtration, whatever. I'm glad they realized it. But, you have to realize that Steve is not a scientist, and that aquarium science in general is a bunch of anecdote for the most part. Some of it is probably very good anecdote and oservations can be very helpful. But, don;t assume that because it is written - be it by Steve, me, or anyone, that it is true, or proven. So, yes, it is kind of an academic question, because regardless of the suppositions in that book or this thread, I can assure you it is not so cut and dry.
>>Basically the detritus is kept in suspension in bare bottom tanks. Marine snow predominates here;<<
No, you (and Steve?) assume it is. I would by no means be prepared to accept that as being true. It might be, and it might not be, but unless there is data to show it, don;t assume it to be true because it looks like it makes sense.
>> and it made me wonder about the whether sand beds may compete with marine snow.<<
Given the bioload of tanks/water volume, consider the following. Lots of detritus produced, virtaully all by the "rock and attached life" and by fish waste. If circulation remains high in the tank, some detritus remains suspended and is either skimmed/filtered or consumed. Some settles. I have yet to see a bare bottom tank that doesn't have any detritus on the bottom....mine always had pockets of detritus. So, let's assume some detritus is going to settle. In that case, either the sand fauna and flora gets to work on it, or bacteria and crustaceans do (in the bare bottom tank).
I have also never seen a tank with an established sand bed that, if stirred, did not have detirtus in it. Therefore, irrespective of ciirculation, some detritus is settling, sand or not...its just a matter of which way/who is going to utilize it - limited flora and fauna or larger diversity flora and fauna. The difference, all things being equal, I guess comes down to the frictional coefficient of bare glass versus sand grains...and that's a pretty small factor in the scheme of things.
>>I note the problem with keeping dendros persists in spite of attempts at heavy feeding with phyto and in sand beds.<<
Have you ever seen if even heavy feeding results in phyto populations equqivalent tothe wild? Neither have I. Also, feeding in Dendronephthya is very dependent on flow speed. With the wrong flow speed, either no feeding or reduced capture rates. So all the phytoplankton in the world might not be helpful. Also, phytoplankton products tend to be Nannochloropsis....a very very small phyto. the small particles may be passing right through the pinnules of the polyp tentacles.
>>Marine snow deficit? I wonder how many other weak nematocyst organisms may be effected by sand bed presence, and whether the sand bed-skimmer combination is the best for some filter feeding organisms, as opposed to EG tanks without skimmers, in which marine snow is preserved, and motile larval forms are fewer.<<
Why does it have to be one or the other? Maybe skimmed tanks need to be fed more often to keep food in the wtaer column? Any food you add to the tank, if not alive, is basically detritus. Our tanks are very low in zooplankton, probably not so low in detritus (if you dont skim heavily). I'd say the zooplankton aspect needs more work than the detritus aspect, in general. But, for most tanks I see, they both need work. I am 100% in agreement with you that we lack the numbers and types of particulate filter feederrs, but think you can blame skimming more than sand beds for that. I know for a fact you don;t need an "EG system" or a "Jaubert" system, or and "Ecosystem system" to run a tank without a skimmer. I think much of this is all hype promoted by those who market it. It's their little "kitch" - the litte tagline they have concocted to become better recognized. All it is is basic biological and ecological processes scaled down to a fragment and in a way that is understandable to them and the masses - and sells a bit, to boot.
>>Also, there isn't a forced choice of either/or. A bare bottom tank without a skimmer, like Steve sets up to conserve marine snow, can also contain a deep sand tower for production of zooplankton. <<
Kee-rist. You gotta be kidding me? I can't even go there.
>>When thinking ahead about how to stimulate nutritional packets in the bulk aquarium water, one has the choice of how to apportion detritus processing, and it seems that this choice might well be made to favor say a coral tank, versus a nonphotosynthetic tank, etc, or to what degree one wished to accommodate certain kinds of habitats. With algal sccrubbers, mud tanks, and bare bottom EG tanks, we do have the ability to determine the mix of particles (larval vs. marine snow, and size) in the tank (but not yet the presence and nature of phytoplankton other thank simply adding it) and it seems little is known about this area- and it may well be important.<<
Of course its important. What's needed is for someone so inclined to go around and sample various tanks and see what's in the water column. then, do the same with various inputs.
You see, all this is contingent on two things - tow very simple things, actually. Primary and secondary production. Primary production can provide the basic energy input to systems. that's pretty much photosynthetic organisms. They use sunlight and inorganic nutrientss and kick off the food chain providing energy as a food souce to everything else (except chemoautotrophs, but let's not go there). In turn, those things that eat the primary producers feed other things or die and feed the microbes. Now, we can't make it in terms of primary production in tanks. We don't an ocean of algae, seagrasses, and phytoplankton to feed the secondary producers, much less at the animal biomass we keep in tanks. That's why we feed the tank. You feed the tank either live foods or dead foods. One can be considered as phytoplankton and/or zooplantkon, the other particulate organic material (marine snow). That's it. Now, if the particulate food is of higher quality than detritus, and we provide enough of it, we don't need detritus at all. If we don't feed enough, we may need the detritus. Basically, we need to provide enough food through light and feeding to sustain everything in the tank and have it grow and reproduce. There are a thousand and one ways to do it. Most people don't do it. I don't even do it, or I'd have all those filter feeders growing in my tank - I have lots more than most people, but not as much as the reef.
So, I need either: more phytoplankton, more zooplankton, more detritus, more large prey items, more bacterioplankton, more dissolved nutrients. That's our choice of foods. I have more dissolved nutrients than the ocean. So, got that licked. I have lots of marine snow - don;t know if its as nutritious as ocean snow, but in looking under a microscope, I seem to have the same amounts as the ocean (no skimming, but also no EG, mud, whatever). Got that licked, I think. So, what am I missing? The other things, obviously. I suspect most people are lacking in the detrital component. So, that means either throwing more food in the tank (could be any component, since detritus is dead material and it will all become dead at some point, even if using live foods), or removing less of it. Lots of ways to do that, too.
Sand beds foster predominantly microbial communities, and are not regenerating nutrients primarily by larvae (which is a good thing as zooplankton levels are likely the most indequate in tanks). We use them mainly to aid in keeping dissolved nutrients lower since the microbes like that stuff and they are generally too high in tanks. They do this pretty well, too. So, I think the answer is either more input or less output with low dissolved nutrients, and sand beds help in this area. Populations in sand beds, if you are concerned about too little detritus and too much larvae (an undue concern, I assure you!), have the advantage of being self limiting. If there is not detritus for them to eat, they don't reproduce, grow, or even live. So, the problem solves itself. And, if you need more detiritus, add some food - flake food even sort of looks like detritus!
>>It may well be that if you take off the skimmer, anything you do from there will be OK, because you are going to have a very dirty and nutritious tank in terms of zooplankton AND marine snow. But it may not. <<
I don;t like the term dirty. But, ok.
>>It may be that an animal adapted to life below a coral flat, in deep water well above the benthic areas, will be irritated by zooplankton, and those adapted to herbivory may well need quality marine snow for protein needs.<<
Irritated? I doubt it. Herbviory and detritovory are two different things. All corals use detirtus as a food source. Some use herbviory. Many use zooplanktivory. Deep water above the benthic area? What are they growing on? benthic area is the bottom - be it shallow water, deep water, rock or sand.
>>I note that the usual ratio of particles in the area in which dendros live is 10 to 1 phyto to zooplankton.<<
Reference, please. But, notwithstanding reference required, that should be almost true anywhere. Remember my tenfold rule? Assume that the phytoplankton to zooplankton food chain is one link...and it generally is. Thus, 10:1 is what should be present. Also, what is "the area where dendros live"?
They - and other herbviorous/semi-herbivrous azooxanthellate corals (and stony corals) have wide habitat ranges. Large Dendronephthya tend to be found most abundantly on steep reef slopes where there is current - has nothing to do with the relative availabilites of phyto/zoo - they live where current brngs them a lot of food at the right speed. But, they and others live elsewhere, too - from near the surface of the water to very deep. And they are pretty much all above the phyto critical depth (P>R), and definitely within the photic zone, so other theoretical arguments here are right out the proverbial window.
>> Is it good for such an animal to be buffeted by so many motile forms it cannot capture?<<
I wouldn's say buffeting does anythin - they just can't use it, that's all.
>> A dendro that cannot capture zooplankton may be starving in our tanks because of the sediment bed processing of what was to become marine snow.<<
No, that's not it. People couldn't keep Dendronephthya years ago either, before sand beds were used. See Delbeek's article at advancedaquarist.com. This was the best attempt to date to provide for these corals and it wasn't altogether successful - although very successful in showing their fastidious requirements.
