Decoupling and adaptation of trophic interactions in aquatic food webs under climate change

Recent climate warming has been shown to advance the seasonal timing of life cycle events, such as budding of trees and egg laying by birds. Species-specific differences in these changes in phenology may result in a decoupling of trophic relationships in food webs and subsequent cascading effects on community structure. For the timing of life cycle events, such as emergence, moulting and sexual reproduction, each species requires specific cues, which are used as proxies for the suitability of the environment for their reproduction and growth. Climate warming may change the validity of the proxies different species use.

The fundamental questions underlying our proposed research are threefold:
1) What proxies do different species use to estimate the suitability of environmental conditions for successful reproduction and growth?
2) Could projected climate warming invalidate the use of these proxies and lead to a decoupling of trophic interactions?
3) Can adaptation to projected climate warming maintain or restore trophic interactions?

Figure 1: Coupling (match) and decoupling (mismatch) of aquatic trophic interactions

Approach
We use a tritrophic pelagic food web to test several hypotheses concerning the impact of climate warming on their phenological coupling. Our experimental model system consists of highly and lowly nutritious algae as primary producers, the zooplankter Daphnia as a key-herbivore, and small planktivorous fish as predominant predators. Experiments are carried out using laboratory systems of different scales, ranging from mesoscale laboratory ecosystems (1000-L Limnotrons), to microcosms and small-scale flow through systems. Lowly nutritious algae are represented by different species of non-toxic cyanobacteria (e.g. Synechococcus), highly nutritious algae quality are represented by different species of unicellular green algae (e.g. Scenedesmus). The herbivorous zooplankters are represented by different species of Daphnia (e.g. longispina group) and sticklebacks are chosen as representatives of an assemblage of small planktivorous fish (0+ fish). Population densities of the different trophic groups will be monitored using the well-approved equipment of the CL, e.g. flowcytrometry, Casy counter, Phytopam and Image analysis. To examine the effect of climate forcing on clonal selection vs. sexual selection, the genetic architecture of the start and end population of daphnids will be determined using PCR-based techniques and allozyme-elektrophoresis. Food quality will be monitored using C: P ratios. We complement these experiments with model analyses of the full ecosystem model for shallow lakes- PCLake.

Techniques to be used: Plankton culture and sampling, microscopy, microcosms, Limnotrons (mesocosms), carbon/nitrogen analyser, photospectrometer, CASY/Flowcytometer, PHYTO-PAM, oxygen measurements, pH measurements, chemical analyses (e.g. total P, total N, P content of algae), physical parameters (light intensity), PCR-based techniques and allozyme-elektrophoresis,data analysis (statistical packages, MS Excel), computer modeling (various setups and programming environments).

Duration
2 - 6 Months, depending on students’ interests.

Period
During fall 2009, sampling campaigns will be carried out throughout Europe, to collect Daphnia resting eggs along a latitudinal gradient (starting in Northern Scandinavia, ending in Southern Spain). Starting January 2010, we will be working on a series of mesocosms experiments where we focus on climate induced changes in the phenological coupling of phytoplankton and zooplankton in the critical response window during spring.

In both these subprojects, up to three students can be employed.

Contact
Dr. L.N. de Senerpont Domis, tel: +31 (0)294 239 385, e-mail l.desenerpontdomis@nioo.knaw.nl