Evaluation of spatio-temporal variation in fish fauna within the Point Calimere Marine Key Biodiversity Area, India.

Biodiversity loss is expanding at an unprecedented rate, owing to habitat degradation, overexploitation, pollution, and climate change. Key Biodiversity Areas (KBAs) play an essential role in conservation and spatial planning to reduce the detrimental effects of biodiversity loss. The present study examined the spatio-temporal variations in fish diversity within selected zones of the Point Calimere Wildlife Sanctuary Key Biodiversity Area (PCWSKBA) from January 2023 to December 2024. In this study, 255 species from 39 orders and 85 families were identified. Escualosa thoracata (Valenciennes, 1847) was the most abundant fish species, comprising 7% of the total number of fish collected, followed by Eleutheronema tetradactylum (Shaw, 1804) (4%) and Mugil cephalus Linnaeus, 1758 (3.8%). The diversity indices revealed that Kodiyakarai Wetland (KW) had the highest species richness and abundance. Simultaneously, the SC recorded lower diversity due to anthropogenic pressure and environmental constraints. The post-monsoon season had the greatest seasonal diversity, which corresponded to the input of nutrients from monsoon rain. The K-dominance curve indicated that the samples from 2023 exhibited a higher concentration of dominance than those from 2024. Redundancy analysis (RDA) revealed that dissolved oxygen, salinity, and phosphate nutrient levels significantly influenced fish distribution across various zones. This study suggests that increasing phosphate and organic matter levels may enhance productivity by promoting algal growth and by providing a food source for fishes. However, excessive nutrient enrichment can lead to eutrophication, depletion of oxygen levels, and promotion of opportunistic species that ultimately disrupt the ecosystem balance. Therefore, it is essential to implement measures to reduce nutrient runoff and organic pollution to prevent oxygen depletion and protect the biodiversity and ecological health of the PCWSKBA. Sustainable land-use practices and enhanced water quality monitoring can help mitigate nutrient overload while preserving the productivity and diversity of aquatic ecosystems.