Nanostructural Chitin Variations in Lagoon Zooplankton under Salinity Stress: A SAXS-based Study from Turkish Coastal Lagoons

Abstract

Objective: This study aims to investigate the effects of salinity and seasonal variation on the nanoscale morphology of zooplankton species (copepods and rotifers) inhabiting five Turkish lagoons: Uzun Lake, Hersek, Dalyan, Çakalburnu, and Paradeniz. The research focuses on chitin-based nanoglobules as biochemical indicators of organismal development and environmental stress. Its relevance spans multiple disciplines, including plankton ecology, biomaterials, and environmental monitoring. Methodology: Small Angle X-ray Scattering (SAXS), a high-resolution biophysical technique, was employed to analyze adult zooplankton specimens collected across different seasons to capture spatial and temporal variability. SAXS profiles were used to determine radii of gyration (RG), pair distance distributions (PDDs), and spatial organization of chitin nanoglobules in copepod carapaces and rotifer mastax structures. These results offer structural information regarding the dimensions of chitin assemblies and the distances between them. Results: RG values of chitin nanoglobules ranged from 21–23 nm, with Dalyan samples showing the most compact and uniform structures. Inter-nanoglobule distances varied by site: 67 ± 1 nm (Uzun Lake), 72 ± 1 nm (Paradeniz), and 76 ± 1 nm (Dalyan). Elevated salinity correlated with disrupted nanoglobule homogeneity and impaired carapace development. SAXS imaging and the nanostructural variations also revealed chitin aggregations linked to developmental stage and ecological stress response of the zooplankton. Conclusion: This study demonstrates the utility of SAXS as a non-invasive tool for ecological nanostructural analysis. The findings establish a strong link between salinity gradients and chitin nanostructure organization, offering novel biochemical insights into zooplankton development and environmental adaptation in lagoon ecosystems. The multi-lagoon and multi-season sampling design, with a focus on chitin nanoglobules, highlights the high potential of this method for developing bioindicators and monitoring lagoon ecosystems.