125 years of change: linking long term observations and network topology to reveal shifts in a coastal food web

Long-term observational data of species composition provide insights into population dynamics and thus into the development of ecosystems across spatial and temporal scales. The analysis of composition data at the network level can help to identify shifts in trophic interactions among species and their contributions to specific ecosystem changes. In this study, we investigated how the coastal food web of a tidal basin in the northern Wadden Sea has changed over the past 125 years by integrating historical and recent species composition data. To assess long-term changes, these composition data were translated into the network dimension using the metaweb modelling framework followed by topological network analysis techniques. Structural changes were primarily reflected in altered predator-prey interactions and network connectance, which were linked to changes in predator composition and the increasing presence of introduced non-native species. However, the trophic composition, the efficiency of energy transfer, and the structural robustness of the food web remained constant throughout the 125-year period. Overall, the food web developed toward its current state, with increased species richness but reduced complexity. The metaweb framework and corresponding topological analyses techniques proves to be a suitable approach for a semi-quantitative analysis of food webs over long time scales, effectively balancing the trade-off between data availability, data consistency, and methodological validity. Reconstructing past changes improves our understanding of the current state of food webs and supports predictions of their future development.