Search

The living conditions for planktonic organisms in the Wadden Sea have dramatically changed during the past (Eriksson et al., 2010) and under progressing climate change these pelagic communities now are facing new threats. Warming winters induce shifts in blooming phenology (Greve et al., 2001) and production patterns of zooplankton (Martens & van Beusekom, 2008; Büttger et al., 2011), and these ecological changes may perturb the pelagic food at different moments of the year. This work investigated for the first time how the pelagic trophic network of the Sylt-Romo Bight, Northern Wadden Sea, changes across (1) spring, summer and autumn seasons and (2) between years which differed in terms of temperature during the preceding winter (2009: warm vs. 2010: cold). We therefore constructed six seasonal carbon flow networks that portrayed material exchanges among 16 trophic groups (bacteria, phyto- and zooplankton, C. harengus) and two non-living carbon pools (POC, DOC) and exchanges with adjacent systems (imports, exports). This approach used linear inverse modeling in combination with Markov Chain Monte Carlo sampling (LIM-MCMC), timeseries data (GPP, NPP, biomass) and literature information (diets, physiological rates) to quantify the carbon flows of the seasonal networks, accounting for uncertainties in carbon flow estimates linked to data constraints. We then applied ecological network analysis (ENA) to assess seasonal and inter-annual changes in the structure and functioning of the pelagic food web (i.e. activity, trophic transfer efficiency, connectance, recycling, flow organization) by means of network-derived whole system indices. Our analysis revealed a pelagic food web that is very inefficient at processing input energy (i.e. high imports and exports; low recycling; low trophic transfer), and this feature highlights its important function in supplying energy to benthic food webs (i.e. high export of POC, unconsumed primary and zooplankton production). Moreover