Environmental gradients and physicochemical properties of water as determinants of mangrove gastropod community structure in Sarawak, Borneo

Mangrove ecosystems are highly dynamic ecological boundaries where water physicochemical properties influence benthic community structure, including gastropod assemblages. This study investigated the relationship between environmental gradients and gastropod community structure in a coastal mangrove system in northern Sarawak, Malaysia. Field sampling was conducted from September 2023 to March 2024 across three stations covering downstream to upstream. Gastropods were collected using quadrats during low tide and identified to species level, while in situ and ex situ water parameters, including salinity, pH, temperature, dissolved oxygen (DO), turbidity, conductivity, ammonia, nitrite, nitrate, and phosphate, were measured. Diversity indices, one-way ANOVA, cluster analysis, Principal Component Analysis (PCA), and Canonical Correspondence Analysis (CCA) were used to evaluate spatial variation. A total of eight species from four families were recorded, with the highest species richness and diversity observed at Station 2 (H' = 1.556), whereas the upstream Station 3 exhibited the greatest dominance (D = 0.3211). Significant spatial differences were detected in the concentrations of temperature, turbidity, DO, ammonia, nitrite, and phosphate, indicating a clear environmental gradient along the river course. PCA and cluster analysis revealed distinct separation of stations, reflecting variation in gastropod community structure. Pearson correlation analysis revealed that pH was significantly and negatively correlated with species dominance; ammonia and nitrite were positively correlated with dominance; conductivity was negatively associated with Ellobium aurismidae abundance; and nitrate and salinity were associated with Cerithidea quoyii abundance. Although CCA suggested tendencies between species distribution and variables such as salinity, DO, and nutrient concentrations, model significance was not supported by permutation testing. These findings provide baseline information on gastropod diversity and water quality characteristics in Sarawak's mangroves and highlight the influence of spatial environmental gradients on community patterns. The study contributes to understanding ecosystem responses to physicochemical change and supports future biomonitoring and conservation of tropical mangrove habitats.