Ecosystem synchrony among small shallow lakes is driven differently by their biotic and abiotic similarities

Identifying the coordinated responses and the drivers of aquatic ecosystem dynamics across space and time is key to understanding and predicting their ecological trajectories under global change. Here, we applied the concept of ecosystem synchrony (i.e., similarities in temporal fluctuations of ecosystem functions across space) to evaluate: (1) the coordinated dynamics of 16 French gravel pit lakes and (2) how geographic proximity, abiotic and biotic similarities explain their level of synchrony. We quantified both long-term (2-years) and seasonal trends (warm vs. cold seasons) in synchrony of dissolved oxygen saturation using high-frequency (10-minute) measurements. We show that long-term trends in synchrony were driven by both abiotic (e.g., nutrient levels, morphometry) and biotic (e.g., fish biomass) similarities between lakes yet the relative influence of these two processes varied seasonally. Seasonal synchrony was indeed primarily shaped by abiotic factors during warm seasons, likely reflecting the stronger control of physical and chemical conditions on ecosystem functioning. Conversely, biotic similarity was more influential during cold seasons, suggesting a greater influence of biological structure under reduced ecosystem productivity. Geographic distance had a negligible effect, likely due to the relatively limited spatial extent of the lake network. These findings highlight the value of ecosystem synchrony as a spatiotemporal integrator of ecosystem dynamics and emphasize the need to account for both the temporal scale and local biotic and abiotic context dependencies when assessing the ecological trajectories of ecosystems.