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[APD] nutrient limitation vs. competition: algae control


Roger, Tom, when you say that algae are not limited by phosphates until
the concentrations are in the PPB, you are not saying that if you
pollute a tank with excess nutrients, you won't get an algae explosion
of some type?

If you don't dump in more nutrients than the system can properly
metabolize at a certain rate, then you would not experience the
explosion; can't we then say we are controlling or managing the algae?

When we have a well tuned system where algae is not rampant, don't the
plants absorb the free phosphates down to the point where algae have a
"tough" time competing for it?

Of course, phosphates are constantly being liberated into solution by
bacterial/biological decay processes; even though the concentration in
the water is very low, the supply is still abundant because of the
continuous flux of phosphate.

At some point, the concentration of a given nutrient becomes the rate
governing factor for growth/reproduction. Growth doesn't cease; it
changes rate. That's the Leibig principle.

When you talk about limitation do you mean a threshold where net growth
cannot occur even though all other non-competitive factors (nutrients,
light) are in abundance? I agree, it is not limitation in this sense
that governs (controls) the algae population.

So maybe we are not controlling algae by limiting them to the point
where they can grow (in isolation) but we are slowing down the growth
and/or reproduction rates to where algae consumers can keep up. Each
type of algae has a different set of consumers. When the system is
modelled with consumers & competitors, you have a kind of dynamic system
control. The laboratory experiments designed to measure the growth
limits of a species, must do so in isolation from competitors. In
isolation, the algae population would increase under a given set of
nutrient concentrations whereas in a dynamic & competitive environment
with the same concentrations, the net population of any one species may

Don't certain types of algae compete with other algae species using
"chemical warfare"? I think there is something to consider that some
types of bacteria would inhibit the growth of other types. When you
consider bio-films, there are complex factors that might govern just who
is able to grow over another neighbouring colony. If you are a biofilm,
once you cover the competition, you have eliminated its access to the
environment. Kill or be killed. Similar factors governing bacterial
bio-film growth upon neighbours might apply to epiphytic algae.

They say that living organisms possess electromagnetic aura. Scientists
can measure these electromagnetic fields. Complex organisms transmit all
kinds of chemical/electrical signals between cells. One of the most
interesting are nerve dendrites. These signals transmit via wave-like
patterns of bio-chemical changes on the cellular surfaces. I wonder if
there might be negatively or positively charged surfaces on submerse
plant leaves? We know about proton pumps in root cells which are used to
attract cations. I wonder if there is molecular level warfare between
epiphytic organisms & hosts utilizing bio-chemical reactions?

Biological systems are heterogeneous; there is never a static
equilibrium. Dynamic equilibria are meta-stable & transitive. Given that
aquarium conditions would be considered eutrophic compared to natural
conditions, its likely that the consumer population density will
increase until the system reaches dynamic equilibrium.

Pong. :-)

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