The effects of physical variables on zooplankton distributions in stratified lakes.

Abstract

Zooplankton play a vital role in lake ecosystems. They serve as an important food source for fish, as well as being major consumers of algae, which contributes to greater water clarity. To understand the dynamics in a lake, it is necessary to understand zooplankton and how they are affected by the physical environment around them. The purpose of this research was to address the question of how turbulence and temperature stratification affect zooplankton aggregations in lakes. Laboratory experiments were performed to quantify the effects of temperature and turbulence on zooplankton distributions in a stratified tank. These measurements were designed to measure zooplankton aggregations and to provide detailed information on the physical conditions causing them. Comprehensive field measurements were taken throughout one summer, covering five 24-hour periods, in order to investigate the effects of temperature and turbulence on zooplankton aggregations in the field. A high-frequency sonar measurement device was developed to take the measurements by modifying the output of a commercial fish-finder and calibrating it to match zooplankton net counts. Our results showed that zooplankton distributions are strongly affected by temperature and turbulence, and that these effects are species-specific, and are different between day and night.