TY - JOUR A1 - Berger, S.A. A1 - Diehl, S. A1 - Stibor, H. A1 - Trommer, G. A1 - Ruthestroth, M. A1 - Wild, A. A1 - Weigert, A. A1 - Jäger, Christoph G. A1 - Striebel, M. T1 - Water temperature and mixing depth affect timing and magnitude of events during spring succession of the plankton JF - Oecologia N2 - In many lakes, the most conspicuous seasonal events are the phytoplankton spring bloom and the subsequent clear-water phase, a period of low-phytoplankton biomass that is frequently caused by mesozooplankton (Daphnia) grazing. In Central European lakes, the timing of the clear-water phase is linked to large-scale climatic forcing, with warmer winters being followed by an earlier onset of the clear-water phase. Mild winters may favour an early build-up of Daphnia populations, both directly through increased surface temperatures and indirectly by reducing light limitation and enhancing algal production, all being a consequence of earlier thermal stratification. We conducted a field experiment to disentangle the separate impacts of stratification depth (affecting light supply) and temperature on the magnitude and timing of successional events in the plankton. We followed the dynamics of the phytoplankton spring bloom, the clear-water phase and the spring peak in Daphnia abundance in response to our experimental manipulations. Deeper mixing delayed the timing of all spring seasonal events and reduced the magnitudes of the phytoplankton bloom and the subsequent Daphnia peak. Colder temperatures retarded the timing of the clear-water phase and the subsequent Daphnia peak, whereas the timing of the phytoplankton peak was unrelated to temperature. Most effects of mixing depth (light) and temperature manipulations were independent, effects of mixing depth being more prevalent than effects of temperature. Because mixing depth governs both the light climate and the temperature regime in the mixed surface layer, we propose that climate-driven changes in the timing and depth of water column stratification may have far-reaching consequences for plankton dynamics and should receive increased attention. KW - Algal spring bloom KW - Clear-water phase KW - Daphnia hyalina KW - Enclosure experiment KW - Phytoplankton KW - Zooplankton Y1 - 2007 UR - https://doi.org/10.1007/s00442-006-0550-9 VL - 150 IS - 4 SP - 643 EP - 654 ER - TY - JOUR A1 - Jäger, Christoph G. A1 - Diehl, S. A1 - Matauschek, C. A1 - Klausmeier, C. A. A1 - Stibor, H. T1 - Transient dynamics of pelagic producer-grazer systems in a gradient of nutrients and mixing depths JF - Ecology N2 - Phytoplankton–grazer dynamics are often characterized by long transients relative to the length of the growing season. Using a phytoplankton–grazer model parameterized for Daphnia pulex with either flexible or fixed algal carbon : nutrient stoichiometry, we explored how nutrient and light supply (the latter by varying depth of the mixed water column) affect the transient dynamics of the system starting from low densities. The system goes through an initial oscillation across nearly the entire light–nutrient supply space. With flexible (but not with fixed) algal stoichiometry, duration of the initial algal peak, timing and duration of the subsequent grazer peak, and timing of the algal minimum are consistently accelerated by nutrient enrichment but decelerated by light enrichment (decreasing mixing depth) over the range of intermediate to shallow mixing depths. These contrasting effects of nutrient vs. light enrichment are consequences of their opposing influences on food quality (algal nutrient content): algal productivity and food quality are positively related along a nutrient gradient but inversely related along a light gradient. Light enrichment therefore slows down grazer growth relative to algal growth, decelerating oscillatory dynamics; nutrient enrichment has opposite effects. We manipulated nutrient supply and mixing depth in a field enclosure experiment. The experimental results were qualitatively much more consistent with the flexible than with the fixed stoichiometry model. Nutrient enrichment increased Daphnia peak biomass, decreased algal minimum biomass, decreased the seston C:P ratio, and accelerated transient oscillatory dynamics. Light enrichment (decreasing mixing depth) produced the opposite patterns, except that Daphnia peak biomass increased monotonously with light enrichment, too. Thus, while the model predicts the possibility of the “paradox of energy enrichment” (a decrease in grazer biomass with light enrichment) at high light and low nutrient supply, this phenomenon did not occur in our experiment. KW - algae-grazer interaction KW - C:P ratio KW - Daphnia KW - ecological stoichiometry KW - food quality KW - light enrichment KW - nutrient enrichment KW - paradox of enrichment KW - population model KW - population oscillations KW - seasonal succession Y1 - 2008 UR - https://doi.org/10.1890/07-0347.1 VL - 89 IS - 5 SP - 1272 EP - 1286 ER -