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> There's a fairly well established ecological principle or theory that
> states that the highest species diversity is found in moderately disturbed
> systems.  Few species can establish themselves in frequently disturbed
> systems, and very stable systems tend to be dominated by a smaller number
> of competitive species.

The intermediate disturbance theory. Boulder size in streams and the
intertidal is the classic examples. But if you have grazers, water changes,
nutrient dosings, etc then what does this now become? If you leave it
completely alone ....yes. Or tear down the tank......you'll get low
diversity. That intermediate "amount, size, method" are those things above.
But if a very stable system such as a reef for instance has high diversity
then how do explain why it does not have completely one species?:-) Niche
diversification comes into play. See below.

> I'm suggesting that in an aquarium that has been substantially unchanged
> for several years there may be a tendency toward dominance of our common
> BGA.  I don't suggest that as a reason for normal BGA outbreaks.

It seems that a stable tank is a very relative term here though. Some folks
have a high NO3 level will most likely not have this BGA if that is their
stable system. If you do have low NO3/ high light I think it is likely to
move towards BGA. If you have a high fish load or an absent one this will
shift things to one niche or the other(say BGA to Green hair).
If you have decent levels of all the nutrients relative to the plants, then
you get plants, little algae. If you play and mess with nutrient levels all
the time then.......etc.
> [snip -- here and there]
>> But are our tanks like lakes and ponds or more like Streams?
> They aren't very much like any of the above.  It is very difficult to
> apply observations from natural systems to aquariums.  One very common
> problem is that the organisms that cause common behaviors in natural
> systems aren't found in aquariums.  For instance, we don't have many
> daphnia or copepods in out tanks, we have a limited diversity among algae
> and there is generally only one type of blue-green algae that is common in
> aquariums.  As a result, most generalizations based on natural systems
> will be wrong when applied to an aquarium.

Then why do so many folks do it and continue:-)? The questions I posed are
rhetorical and food for thought(s).
> I suggest with caution that the natural correlation between high stability
> and a tendency toward dominance may carry through to aquariums.
> I don't
> feel real bad about doing that because the correlation is common to a wide
> variety of natural settings; reefs, estuaries, reservoirs, forests,
> deserts, prairies, alpine meadows, and on and on.  It is not dependent on
> the behavior of any one organism or even any group of organisms.

These ecosystems are complex though. They include predators preying on the
prey that helps inferior species to gain an upper hand and persist. So can
ours if we add predators (like the herbivore) to eat the prey(algae). Some
predators are omnivorous which makes things even more complexing.
> Further, you can actually watch this happen among the plants in a planted
> tank.  If you let a tank go for a while you end up with just one or two
> plants taking over and squeezing everything else out.
>If you want to maintain a variety of different plants in a planted tank then
> you have to get in and prune, remove extra plants and move plants around; that
> is, you
> have to disturb the system. Since it happens to plants in a planted tank I
> suspect it may also happen to other parts of the tank population as well.
> There are several methods, but I would be very surprised if any non-lethal
> method (including blackout and fertilizer) is going to be 100% effective
> for anyone, much less for everyone.  Different problems have different
> causes and need different solutions.

But the BGA will come in again even if you use antibiotics. There are no

>> I think it's more likely poor conditions that favor the BGA's(high light/low
>> nutrients/stagnant water) and not so much a resistant strain.
> People on this list have reported severe BGA outbreaks under a wide range
> of conditions -- many of which are "good" conditions by any measure.  One
> thing I can say without any fear of being wrong is that the common green
> slime BGA that we get in our tanks is *not* uniquely linked to high light
> and low nutrients.  In fact, it is probably more common in polluted tanks
> with low light.

But if a tank is polluted etc and has high levels X, Y and Z then it's
pretty disturbed. Not a good place for much plant life besides algae. Often
you will see successional stages of algae presence in such polluted tank
also. Many new folks go through this green hell. Folks alter one nutrient
then the other in a vicious cycle.

Diatoms & GW-> Green fur/BBA(short greens)-> BGA-> green hair(long hair
Cladophoras) algae seems to be much of the likely patterns in tanks. BBA
creeps in in a number of spots. Sometimes the BGA takes the 2 nd spot. It's
hard to say exactly. But it could be figured out I believe based on the
nutrients available/disturbances.

> Tom, could the idea that BGA is favored by high light and low nutrients be
> one of those observations from natural systems that doesn't apply very
> well to aquariums?

Yep, it does work so it's _very likely_ just correlational, not causal.
Never know what happens when you mess with nature:-) Not a bad idea to look
into it though.........

>  That might be possible because the BGA that create
> that trend in natural systems are not common in aquariums or because in
> the controlled environment of our tanks there are other more prominant
> factors.

Like CO2, herbivores, current, nutrient additions, pruning manual removal
water changes, lighting changes etc etc etc.............
A number of the natural BGA are heterocyst formers. What % of N they get
from the air and the water is unclear from what I've read so far.
Tom Barr
> Roger Miller
> ------------------------------