Assessment of the influence of species’ functional traits-environmental variable associations on the occurrence and abundance of non-marine Ostracoda (Crustacea) in Manisa province (Türkiye)

Abstract An understanding of how functional traits correspond to environmental conditions is essential for assessing species–environment associations. In this study, we examined functional trait–environment interactions affecting ostracod abundance across 122 aquatic sites in the Manisa Province (Türkiye) and identified 62 ostracod taxa, including 42 living species, four living unclassified taxa, and 16 subfossils. Using canonical correspondence analysis, we identified manganese (Mn 2+ ), electrical conductivity (EC), and potassium (K 1+ ) as the most influential factors among 13 environmental variables affecting the distribution of ostracod species. Multivariate functional trait-based analyses revealed that length of the swimming setae on the second antennae (A2), uropod development, and carapace length explained a significant portion of ostracod abundance, with a fourth-corner correlation of 60%. These functional traits were found to be strongly associated with key environmental gradients, EC, dissolved oxygen, K 1+ ⁺, Mn 2+ , sediment grain size, and habitat type. Double-constrained correspondence analysis indicated that the first axis explained 35.7% of the joint functional trait–environment variance, while both the functional traits set and environmental variables set each accounted for 23.7% of the total abundance inertia. Among all functional traits, carapace length was the most influential trait explaining the species abundance that was strongly associated with Mn 2+ , pH, habitat type, and water temperature. Lotic habitats tended to support species with reduced swimming setae, while smaller-bodied species were more associated with pH, sediment grain size, and Mn 2+ gradients. Overall, our findings demonstrate that functional traits provide meaningful insights into how ostracod species respond to environmental variation. Functional trait-based approaches therefore offer a powerful tool for understanding community assembly processes and for improving biomonitoring of freshwater ecosystems.