Phytoplankton at the Crossroads: How Geography and Environment Shape Communities in 70 Lentic Systems (Türkiye)

Abstract In 70 lentic systems across Türkiye, phytoplankton communities and environmental variables were analyzed using samples collected during the spring, summer, and autumn of 2017–2019. The study aimed to assess the influence of both spatial and environmental factors on phytoplankton assemblages. The lentic systems were categorized into six ecoregions. Differences in these regions were examined in terms of environmental parameters, phytoplankton community structure, and ecological quality status. Additionally, the degree of influence of spatial and/or environmental factors on phytoplankton distribution was determined using two-way indicator species analysis (TWINSPAN), Moran's Eigenvector Maps (MEMs), Redundancy Analysis (RDA), and variation partitioning analysis. The differences observed in environmental factors across Türkiye's six ecoregions in terms of latitude and longitude are actually a reflection of various factors such as climate, geological structure, altitudinal differences, and anthropogenic effects. These differences affect phytoplankton species composition, the distribution of dominant species, phytoplankton biovolume, the ecological quality of systems, and species richness. Although TWINSPAN indicates that geographical proximity partially affects species composition distribution, MEMs and variance partitioning show that the fraction of variance uniquely explained by spatial (latitude and longitude) autocorrelation was more important for dominant species distribution. Ultimately, our findings provide compelling evidence that phytoplankton community composition is both driven by spatial factors and environmental factors, challenging overly simplistic views and reinforcing the need for multifactorial perspectives in ecological typology.