Plankton dynamics in planktivore- and piscivoredominated mesocosms
Bertolo, Andrea; Lacroix, Gérard; Lescher- Moutoué, Francoise; Cardinal-Legrand, Catherine
Archiv für Hydrobiologie Volume 147 Number 3 (2000), p. 327 - 349
published: Feb 3, 2000
ArtNo. ESP141014703008, Price: 29.00 €
We present the results of a 2-months replicated mesocosm experiment, in which we assessed the effects of both planktivorous and piscivorous fish on plankton. We compared systems with 2 (zooplankton and phytoplankton), 3 (planktivorous perch - Percafluviatilis - zooplankton and phytoplankton) and 4 trophic levels (piscivorous and planktivorous perch, zooplankton and phytoplankton). We designed the 4 trophic levels treatment in order to obtain a very strong control of the third trophic level (planktivorous perch), increasing the total nutrient budget by introducing supplementary prey fish in the enclosures. Classical cascading responses to fish were observed. In the planktivore-dominated systems, algal biomass significantly increased, whereas algal biomass was similar in the piscivore-dominated systems and in the control treatment. The two functionally even-link systems (systems with an even number (2 and 4) of trophic levels) responded in a similar way, despite the overall increased nutrient load in presence of the piscivorous fish (ca. 17 % > controls). Fish seemed to induce an earlier maturity of the dominating herbivorous Ceriodaphnia: we discuss the consequences for zooplankton dynamics. Furthermore, the lack of the large-bodied Daphnia in the systems did not hinder the control of algae in even-link systems by medium-sized herbivorous zooplankton.