In contrast to previous assumptions, the isotope results from this study showed that the majority of the energy of the food web is produced by algae on intertidal mudflats within the Wadden Sea itself, instead of by algae imported from the North Sea or rivers. In addition, researchers found large differences between different parts of the Wadden Sea that were located relatively close to each other. In the study, an exceptionally high spatial resolution (9165 samples from 839 locations) and taxonomic resolution (178 species) was obtained by making use of an extremely large sampling scheme, in combination with several other sampling efforts.

Sander Holthuijsen, NIOZ assistant and technical coordinator of the Waddensleutels project: “For almost a decade, several weeks each summer, a team of NIOZ scientists and many volunteers sails with NIOZ’s research vessel Navicula across the Dutch Wadden Sea, one of the world's largest intertidal ecosystems, to assess the state of the intertidal macrofauna (SIBES). Combining Waddensleutels with SIBES’ 5000 sampling stations really made the difference. In no other way both biomass and isotope data could have been sampled in such an extensive way.”

The RV Navicula during the SIBES project mission on the Wadden Sea.

Largest food web study for a single region

At NIOZ, the sampled material was analyzed for its stable carbon isotopes, a technique which enables to trace the sources of carbon in food webs. “The amount of isotope data we generated was unprecedented and the largest ever accumulated for a single region”, according to NIOZ-researcher Stefan Schouten who led the stable isotope analysis.

These findings have important implications for understanding the functioning of food webs and for the management and protection of the intertidal flats that sustain the dominant food and energy suppliers for the Wadden Sea. The findings show the need for long-term ecological research and environmental monitoring programs to sample at high spatial resolution, not only for macrofauna but also for microphytobenthos.

This research was a collaborative effort of three Dutch research institutes; University of Groningen, Utrecht University and the Royal Netherlands Institute for Sea Research and two nature conservation organisations (Natuurmonumenten and Staatsbosbeheer) within the Waddensleutels program. This program focused on the importance of habitat modification by reef builders (predominately mussels and oysters) for food web dynamics and biodiversity in the Wadden Sea. This research was funded by the “Wadden Fonds”.

Christianen, M.J.A., Middelburg, J.J., Holthuijsen, S.J., Jouta, J., Compton, T.J., van der Heide, T., Piersma, T., Sinninghe Damsté, J.S., van der Veer, H.W., Schouten, S. and Olff, H. (2017), Benthic primary producers are key to sustain the Wadden Sea food web: stable carbon isotope analysis at landscape scale. Ecology 98, 1498–1512.