Biological Communities of Lakes and Reservoirs

Plankton

The plankton community is the group of tiny plants and animals that drift, float, or weakly swim in the water column. This community is much more dense and diverse in lakes than in streams due to reduced water current. Planktonic plants, called phytoplankton, include photosynthetic algae and bacteria, such as Cyanobacteria. Planktonic animals, called zooplankton, are composed primarily of protozoans, rotifers, and microcrustaceans, such as Cladocera and Copepoda, which feed primarily on phytoplankton.

Benthos

The benthic community is composed of bottom-dwelling invertebrates. The composition of this often-diverse community varies from shallow shore areas (littoral) to deeper portions of the lake-- sublittoral and profundal (very deep) regions. The benthos may be populated by sponges, coelenterates, rotifers, nematodes, bryozoans, crustaceans, mussels and clams, snails, insects, and leeches.

Nekton

Larger open-water (pelagic) animals include the fishes. Some members of this community, such as Ameiurus bullhead catfishes, are closely associated with the bottom. Fishes occupy multiple trophic levels in the lake food web, with various species consuming everything from detritus and plants to the top predators.