Lignell, R. Finnish Environment Institute/Research Team PELAG (FEI-PELAG), risto.lignell@vyh.fi
Tamminen, T. FEI-PELAG, timo.tamminen@vyh.fi
Heiskanen, A. FEI-PELAG, anna-stiina.heiskanen@vyh.fi
Seppaelae, J. FEI-PELAG, jukka.seppala@vyh.fi
Kuuppo, P. FEI-PELAG, pirjo.kuuppo@vyh.fi
Tuomi, P. FEI-PELAG, pirjo.tuomi@vyh.fi
Olli, K. Institute of Botany and Ecology, University of Tartu, olli@ut.ee

 
PLANKTON ECOLOGICAL STUDIES IN LARGE-SCALE MESOCOSMS: NUTRIENT VS. PREDATION CONTROL AND RETENTION VS. EXPORT OF NUTRIENT LOAD
 
Five 2-3 week mesocosm experiments with variable nutrient (N, P and Si), sucrose and top predator (fish larvae) treatments were carried out in summers, in the brackish northern Baltic Sea. The results demonstrate the strong interplay between bottom-up nutrient limitation of the plankton community biomass, and top-down predation control of the food web structure, biotic interactions and resilience, and the role of these regulators in retention of nutrient inputs in the trophogenic layer. Repeatability of food web responses was good (low variance between triplicate nutrient units) as was inter-annual reproducibility of key features, such as consistency in the 'critical nutrient load' causing 'bifurcation' of the system to a new stationary state. Depending on the initial conditions of the community, on the nutrient supply mode (continuous vs. pulsed), and on additional treatments, nutrient additions could be channeled to 'new production' type bloom peaks of opportunistic microphytoplankton species followed by export from the trophogenic zone, to enhancement of the microbial loop, or to efficient retention of especially P. In conclusion, understanding the 'model' systems confined in mesocosms is a key step in understanding the more complex dynamics of natural plankton communities and predicting their response to external stress, such as nutrient load.
 
Day: Thursday, Feb. 4
Time: 09:15 - 09:30am
Location: Eldorado Hotel
 
Code: SS51TH0915E