Aquatic community synchrony dynamics in response to multitrophic regime shifts: Paleoecological insights from a...

Ecological synchrony, the coordinated fluctuation of species or communities, is central to ecosystem stability. Yet how synchrony changes during ecological shifts remains poorly understood. This gap is particularly evident in shallow lakes, where transitions from clear, macrophyte-dominated to turbid, algae-dominated state can dramatically alter synchrony patterns, challenging ecosystem resilience. Here, we integrate century-scale multi-proxy sedimentary records (algal pigments, macrophyte macrofossils, diatom and cladoceran remains) with remote sensing data, to investigate both intra- and inter-community synchrony dynamics throughout multitrophic regime shifts in Lake Liangzi, an iconic shallow lake in eastern China floodplain. Our results reveal that the lake ecosystem experienced two distinct ecological shifts, occurring around the 1960s and 2010s. The lake was initially submerged macrophyte-dominated with low macrophyte community synchrony and limited phytoplankton abundance. Since 1960, the lake entered a gradually transitional phase due to damming and agricultural impacts, with nutrient enrichment, increased algal production, and macrophyte shifts to emergent floating groups. Correspondingly, the synchrony of algal community decreased, but macrophyte synchrony increased towards decline in community stability. Around the mid-2010s, the lake shifted to an algae-dominated regime, characterized by algal proliferation at low synchrony and sustained high synchrony within the degraded macrophyte community. Our ordination analysis identified hydrological regulation, intensified nutrient loading and rising temperatures as main drivers underlying the regime shift. The findings highlight how ecological synchrony modulates ecosystem resilience to environmental disturbances. This study underscores the importance of asynchronous responses in bolstering ecological stability and that synchrony should be recognized as a key indicator of ecological state transitions in shallow lakes.