Separating effects of climatic drivers and biotic feedbacks on seasonal plankton dynamics: no sign of trophic mismatch

Abstract

Summary Climate change may impact most strongly on temperate lake plankton communities in spring, when light availability and water temperature change rapidly due to thermal stratification. Effects of changing light and temperature on one food‐web component transfer to other components, producing a complex interplay between physical drivers and biotic feedbacks. Understanding this interplay is important, because altered climate regimes could result in phenological mismatch between the phytoplankton spring bloom and the timing of maximum food requirements of grazers. To separate direct effects of light and temperature on spring plankton dynamics from effects mediated through micro‐ and mesograzer feedbacks, we manipulated water temperature, stratification depth and presence/absence of the mesograzer Daphnia in lake mesocosms. In early spring, stratification depth and water temperature directly influenced the light supply to phytoplankton and the growth rates of all plankton groups. Subsequently, indirect effects, including light‐dependent food supply to grazers and temperature‐dependent grazing pressure, became increasingly important. Phytoplankton and Daphnia peaked earlier in warmer treatments and reached higher peaks when stratification depth was shallower. Ciliates responded positively to increased food density and higher temperature and subsequently affected the taxonomic composition, but not the total biomass, of phytoplankton. In the absence of Daphnia, phytoplankton did not enter a distinct clear water phase. When present, Daphnia caused an extended clear water phase, maintaining phytoplankton and ciliates at low levels throughout early summer and suppressing all direct effects of physical drivers on these plankton groups. Our Daphnia treatments mimicked the high and low fish predation settings of the largely descriptive, recently revised Plankton Ecology Group (PEG) model of seasonal plankton succession and explored their responses to climate change scenarios. The results largely support the PEG model, but attribute greater importance to early season temperature effects and later season grazing effects of Daphnia. In warmer treatments, the timing of phytoplankton and zooplankton peaks tended to be more closely coupled, and temperature did not affect the height of zooplankton peaks. In line with other experiments, these results do not support the widely held concern that warming may create a trophic mismatch between phytoplankton and zooplankton and reduce spring zooplankton production.

Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

“…Unfortunately, putatively important drivers of metazoan zooplankton seasonality, such as temperature, were not included in the updated version of the PEG model, despite many studies highlighting the importance of temperature for zooplankton spring phenology (Gillooly & Dodson, 2000;Straile et al, 2012). In particular, the PEG model should be modified by including the role of temperature in regulating zooplankton seasonality during winter, and especially during spring in both eutrophic and oligotrophic lakes (see also Berger et al, 2014). Furthermore, data from Lake Constance presented here suggests that the role of food limitation during spring, that is after the onset of the phytoplankton spring bloom, as a driver for zooplankton seasonality has been overestimated in the PEG model.…”

Integrating chytrid fungal parasites into plankton ecology: research gaps and needs

“…Planktonic organisms experience dynamic changes in resource availability at different temporal and spatial scales, not only as a result of seasonality or changes in mixing regimes, but also due to climate change and anthropogenic impacts (Behrenfeld et al, 2006;Berger et al, 2014). Shifts in the availability of nutrients affect phytoplankton growth and its elemental composition, which may in turn propagate to higher trophic levels (Sterner and Elser, 2002;Berger et al, 2006;Van de Waal et al, 2010;De Senerpont Domis et al, 2014).…”

Phytoplankton Functional Groups Variation and Influencing Factors in a Shallow Temperate Lake

“…Water temperature was one of the most important environmental factors influencing the growth of phytoplankton in lake ecosystems (Pinto et al, 2014;Schagerl and Oduor, 2008). Furthermore, Berger et al (2014) reported that water temperature directly influenced the growth rates of all phytoplankton groups in early spring. Different phytoplankton species can tolerate different ranges of water temperature, nutrient, and light availability, which could be a guide for determining the tolerance levels of different species for different seasons (Akbay et al, 1999).…”