Zooplankton

Abstract

Zooplankton are usually defined as small free-swimming animals that can be caught in nets. Zooplankton range in size from about 0.1 mm to 1-3 mm in length. The main components of the Zooplankton are protozoa, rotifers, and crustaceans. Although rotifers may be more abundant numerically, the crustaceans generally constitute most of the biomass. They include the cladocerans, cyclopoids, and calanoid copepods. Some Zooplankton are herbivorous and feed on phytoplankton or bacteria, whereas others are predatious and feed on other Zooplankton. Zooplankton, in turn, are fed upon by small fish. Zooplankton are an important component of the herbivore food chain and are often considered to be the main agents responsible for cropping the phytoplankton population. Although it is unlikely that Zooplankton graze significantly on blue-green algae, they probably play an important role in cropping the eucaryotic algae (see Chapter 4). An understanding of the dynamics of Zooplankton is therefore important if we are to understand the food chains of the lake.