Salinity-Mediated Structuring and Marine–Estuarine Connectivity of Penaeid Shrimp Assemblages in Ashtamudi Wetland, India

Abstract

Salinity gradients play a critical role in structuring penaeid shrimp assemblages in tropical estuaries. The present study aimed to evaluate salinity-driven spatial segregation, diversity structure, and marine-estuarine connectivity of penaeid shrimps in Ashtamudi Lake, a Ramsar-designated wetland in Kerala, India. A comparative cross-sectional ecological research design was adopted, involving short-term field sampling conducted in January 2024 across two ecologically distinct salinity zones: the marine-dominated Neendakara sector and the marine-brackish Puthenthuruth sector. Specimens were collected using standardized fishing gears and analyzed through quantitative community assessment methods, including species richness estimation, Shannon–Wiener and Simpson diversity indices, Sørensen similarity index, K-dominance curves, habitat-based functional classification, and hierarchical cluster analysis. A total of 23 species were recorded from the marine zone and 17 species from the brackish zone, with overall abundance markedly higher in the marine sector and deep-sea taxa absent in the lower salinity area. Diversity indices indicated greater community stability in Neendakara (H′ = 3.031; 1-D = 0.948) compared to Puthenthuruth (H′ = 2.511; 1-D = 0.900). Despite reduced richness, species overlap between zones remained high (Sørensen index = 0.85), reflecting strong ecological connectivity. Migratory marine-estuarine penaeids constituted 26.1% of total species diversity, highlighting the nursery function of the estuarine sector. The findings confirm salinity as a primary ecological filter regulating penaeid community assembly and emphasize the need to maintain hydrological integrity for sustainable fisheries and biodiversity conservation.