Seasonal variations in planktonic food web structure affect stability by shifting the distribution of energy fluxes

Seasonality in temperate ecosystems shapes species phenology, influencing interactions and food web structure. Variations in species richness and biomass affect trophic interaction strength, a crucial factor for community stability, which can be assessed through energy fluxes—an essential indicator of ecosystem function. Yet, we still have limited understanding on how energy fluxes and food web structure vary overtime and how the seasonal dynamics influence stability. We examined how the structure, energy fluxes, and stability of a highly resolved multitrophic lake food web change across seasons over three successive years. Two estimates representing different facets of stability were considered: resilience and reactivity. We found a strong seasonal pattern in food web structure, with higher complexity observed in summer and autumn. In addition, we found that more complex food webs are more reactive to perturbations, and consequently, less stable than simpler ones over short time-scale. This was influenced by a lower proportion of strong energy fluxes. Resilience was unaffected by seasonality, food web structure and energy fluxes, highlighting the need to account for multifaceted nature of stability. The seasonal variability of stability suggests that food webs may vary temporally in their vulnerability to environmental perturbations, which has important implications for ecosystem management.