Further observations on limnetic zooplankton in a small lake and two enclosures containing fish

SUMMARY. In a small lake (Blelham Tarn, English Lake District) two plastic cylinders, each of which extends from the lake surface to the bottom sediments and encloses 18 000 m³ of water, were used to investigate effects of enclosure on the zooplankton. This paper describes observations from March 1973 to October 1974 and is the second part of a report on a project spanning 4 years.
Seasonal population densities of the more abundant species were essentially similar to those observed in the first part of the project, despite large changes in algal and predator populations. In the enclosures, fish (mostly Perca fluviatilis ) populations are known from observations by divers to have been large in the period under consideration and small in the first part of the project. Populations of Chaoborus larvae in the enclosures were small at all seasons from March 1973 to October 1974.