3. Molluscs - filter feeders, clams and mussels, Corbicula, zebra mussels, and deposit
feeders, snails.
4. benthic crustacea - Ostracoda, Cladocera (Sida), crayfish, etc.
5. Other groups - mostly filter feeders, bryozoans (Pectinatella), sponges (Spongilla
spongillis), Hydrozoans (Craspidecuspa).
III. Microbial assemblages - (except algae)
A. Bacteria - functional classes
1. Photosynthetic bacteria (not cyanobacteria)
2. sulfur or metal reactive bacteria, Metallogenium, Chlorobium
B. Fungi - the Phycomycetes, Saprolegnia, Lagenidium
C. Protozoa, Vorticella, Stentor, Paramecium, Amoeba - sometimes deadly parasites
(Acanthamoeba, Naegleria), or merely parasitic (Epistylis on fish).
Such classifications are promoted as simplifying and organizing the great diversity of aquatic life. These
designations are never perfect, however. The plankton, for example, contains microbes, phytoplankton
and zooplankton, and a large variety of meroplankton, larvae that temporarily inhabit the plankton. The
aufwuchs (periphyton) also contains microscopic plants, animals, bacteria, as well as worms, and
benthic insect larvae. At some very fine scale, the organizational relationships become unmanageable
except within the context of individual life histories.
Here we concern ourselves with what the organisms do. And it is here that the ecologists have
constructed elaborate predictive systems to organize the apparent chaos that we discovered in the
previous section. Distributions
Vertical distributions and longitudinal distributions through reservoirs are greatly affected by
stratification and flow patterns. During mixed conditions plankton are often well-distributed throughout
the depths of a reservoir. While the lake is mixing, cells are periodically brought into contact with the
lake surface where light is available and the motion of the water causes greater contact with nutrients.
Such conditions are favorable for productivity. For this reason, the early spring and the fall are often
times of increased planktonic biomass.
As stratification begins, heavier particles tend to sink and settle out of the water column. Diatoms
and larger planktonic cells commonly do this. In the northern natural lakes there was a trend for the


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