Responses of zooplankton to long-term environmental changes in a small boreal lake

Zooplankton dynamics were examined in a small boreal lake over a 20-year period and interpreted in relation to climate change, brownification and recovery from acidification. Significant changes were recorded in the abundance of dominating crustacean species but not of rotifer species. According to redundancy analysis (RDA), the long-term pattern in crustacean zooplankton was mainly associated with abiotic factors like water colour, alkalinity and total phosphorus. Primary production of phytoplankton was the most important biological parameter whereas planktivorous perch and Chaoborus larvae had a marginal contribution. Biological factors were relatively more important for rotifers than for crustaceans, primary production being the most powerful explanatory parameter, followed by alkalinity, total phosphorus and colour. The changes in the zooplankton community were mainly related to increased organic carbon load and recovery from acidification. Within the food web, bottom-up regulation seemed to exceed the importance of top-down control.