Evaluation of the responsiveness of the crustacean zooplankton community size spectrum to environmental change and an exotic invader in a sample of Canadian Shield lakes

Abstract

We evaluated the crustacean zooplankton size spectrum as an indicator of lake characteristics and ecosystem change. First, we used time-series from seven Canadian Shield lakes to identify the factors associated with among-lake and among-year variability in the spectrum slope (relative abundance of small and large zooplankton) and centered height (total abundance). Second, we used time-series from an invaded and three control lakes to assess change in mean and variability in slope and height due to a Bythotrephes invasion. We found that the slope and the height reflected among-lake predictors related to morphometry. The slope was responsive to long-term declining lake phosphorus levels, whereas the height reflected both increases in dissolved organic carbon and decreases in ice duration. We detected a significant increase (i.e. flattening) in mean slope and substantial (up to 120%) increases in the CV of height after Bythotrephes invaded Harp Lake. Thus, the zooplankton size spectrum was responsive to long-term environmental change and a strong top-down perturbation can be detected through regular and frequent monitoring programs.

Advantageous and Disadvantageous of Non Classical Biomanipulation

“…Shift in community structure can be achieved by five different methods that can be used collectively or separately: decrease in water level, fish poisoning, fish winter killing, removal of fish and piscivorous fish stocking [7]. It is evident that zooplankton can control phytoplankton, but results can be variable [7][8][9][10][11][12][13][14], as compared to planktivorous fish [5,8,15,16]. Due to peculiar processes and structures which are highly variable, outcome of biomanipulation is difficult to measure quantitatively.…”