Aerobic and anaerobic bacteria, cyanobacteria,
ascomycete fungi, oomycetes, yeasts, diatoms
and algae soon create quite a resource: a
protected habitat with increasingly varied
opportunities for the first grazing protozoans, which move into the mucus-like coating. Their
grazing patterns start to create a patchy
mosaic, which you could think of as a network
of "edge" habitats. Picture the
patchy mosaic of algae an Otocinclus leaves
on a piece of driftwood. It's a general phenomenon
of ecology, true at every scale, that edge
habitats characteristically encourage the
richest biodiversity.
Sessile protozoans, such as ciliates and flagellates, settle
down to their sedentary existence, where
new "trophic webs" develop. Soon
the more mobile multicellular organisms,
like microscopic
gastrotrichs and
rotifers, squirming nematodes
and naidid worms,
and the even more mobile
water mites and the smallest crustacea, such as copepods,
find sources of nutrition in the developing
biofilm. The more complex the biofilm is,
the more variety it offers mobile grazers
and predators to pick and choose, and, interestingly,
the more stable it becomes. At the top level,
these diverse microscopic meadows are grazed
by snails and our familiar "algae-eating"
fish.
Though the ecologists' name for this community
coating the substrate and all other underwater
surfaces is the "benthos," aquarists
are more likely to refer to it as the "biofilm."
Links.
Biologists who study this "zoobenthos"
ecosystem have naturally concentrated on
the creatures that are typical of northern
temperate climates. After all, the scientists
themselves are mostly northern temperate-raised
scientists with degrees from northern-temperate
universities; however, very much the same
kinds of creatures also form the tropical
zoobenthos, it appears. Even though the actual
species involved are ordinarily different,
the kinds of species and their interactions are largely
parallel. If you're interested in knowing
more about the benthos of natural freshwaters,
relevant to tropical freshwaters and so to
our aquaria-- then check out the rich Nova
Scotia-based Freshwater Benthic Ecology and Aquatic Entomology
Homepage.
A well-illustrated succinct description of biofilm, whether on wet aquarium surfaces or between
your teeth, more detailed
than what you've
been reading here, but
free of jargon, has
been created by John E.
Lennox at Penn State.
