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Re: algae

I opined:

>> Most of use don't use a rich substrate and our aquarium plants have to
>> compete head-to-head with the algae for dissolved nutrients.  There must
>> be something in our aquariums that tilts the advantage to the plants,
>> because with the same nutrient levels under natural conditions the algae
>> will usually squeeze out the plants.

to which Tom Barr replied:

> What exactly is this thing though. I've tried the highest lighting and
> rich substrate with little water column nutrients. I've tried the water
> column heavy approach as well with high light again. Got better results
> with the water column..........it doesn't match but then again we are
> adding CO2, stable nutrient supply etc

I've had pretty good success keeping tanks free of nuisance algae by using
moderate-to-bright light and fairly heavy substrate fertilization with
little more than wastes from a light fish load added to the water column.
I'm moving away from that now, partly because of the "been there, done
that" effect, partly because that approach is difficult to keep up and
partly because some plants seem to look better when they get ample
water-column fertilizing.  But then, some plants look better when given
good substrate fertilizing, so I'm still going to keep fertilizing those
plants in the substrate.

>> The other thing that we don't see is that algae have relatively high
>> energy and material demand compared to plants.  Phytoplankton don't
>> just float around all day; they swim, and that takes energy.

> Green water does and so do BGA's. Most that bug us are attached or
> entangled like Cladophora. Their gametes swim (in most cases) though,
> but that's no big deal.

I may have to back off the "energy advantage" argument.  It goes a pretty
good job of explaining why some algae do better than others in our tanks,
but I'm not so sure that it explains the difference between submersed
plants and algae.

>>> But since algae can live in low and in high levels of nutrients and
>>> are seeming more efficient, why do the plants continue to dominate?
>>> Algae is still there but it's not dominating. There's plenty of
>>> nutrients for the algae as well as the plants. Why then is this
>>> happening? It seems like a contradiction.

>> I agree, but I wonder if the advantage has much at all to do with
>> nutrients.

> That's what I think to a degree, how much? Less than being said often on
> list IMO.

I think that the nutrient setup in a water-column fertilized tank actually
favors algae over plants.  Whatever the offsetting factor is (or factors
are, as I suspect there are several operating simultaneously) their
combined effect must be strong enough to offset the nutrient advantage we
give to the algae.

>> Especially in our tanks, where the grazing species are selected so that
>> plant grazing is discouraged and algae grazing is encouraged.  Algae
>> grazing isn't limited to the macroscopic grazing we see and promote.
>> It also occurs on a microscopic level.  Some protozoans, for instance,
>> feed on algae.

> How much do they contribute to our tanks though? Good question there.

We tend to ignore things that we can't observe directly, or attribute
their effects to other factors we can observe.  There is substantial
evidence that under natural conditions various sorts of microscopic phages
pose important controls on algae populations. These may be protozoans, but
many are bacterial and even viral phages.  I figure that pretty much
anytime we see algae disappear from out tanks without a change in
macroscopic grazing that we're seeing the micrograzers at work.

>> If I understand what you're saying then I think that would be
>> consistent with sugars leaked by the nutrient-limited plants actually
>> feeding the algae.  A big water change removes the products already
>> leaked from the plants and takes away the suppliment that the sugars
>> gave to the algae.

> Sounds good, I like the idea.

I'm still not sure that this mechanism is real, so I've spent some time
wondering if we see other behaviors in our tanks that might be due to this
"feeding" effect.

For instance, it seems to me that a big aerated trickle filter should
strongly favor bacterial consumption of the leaked sugars over algae use
of the sugars.  If that mechanism works, then it seem like
nutrient-limited tanks with big trickle filters might experience fewer or
different kinds of algae problems compared to similar tanks that are
equipped with canister filters.  In particular, if a tank is switched from
a canister filter to a trickle filter (or vise versa), is there a change
in the frequency, severity or nature of algae problems?

> Best explaination so far in my book! But it sounds multivariable and
> that would make sense on why it's so hard to pin down. Differences in
> growth oscillations, herbivory levels, protoza (in some cases?), water
> changes, nutrient ranges and consistency, and there's more........well
> perhaps that ecological modeling class will help me put all this
> together.

Cool course.  No-one has (yet) given me free reign to run one of those
habitat models.  The ones I've studied are too general to match to the
sort of observations we make in our planted aquariums.  I have a partly
completed model that I wrote myself specifically for simulating
relationships in planted aquariums; my work on that ground to a halt when
I faced the problem of simulating an organism as complex as a plant.

Roger Miller