Biodiversity Dynamics and Ecological Stressors in the Caspian Sea: Integrating Pollution, Climate Change, and Microbial Interactions

The Caspian Sea, the largest enclosed inland water body on Earth, hosts a unique and vulnerable ecosystem characterized by high levels of endemism and complex ecological interactions. Over recent decades, anthropogenic pressures including pollution, overfishing, habitat degradation, and climate-induced sea level decline have led to a severe biodiversity crisis. This study synthesizes updated data from ecological surveys, pollution monitoring, and microbial community analyses to assess biodiversity patterns and environmental stressors in the Caspian Sea from 2010 to 2025. Using a combination of field-based indices (Shannon–Wiener diversity index, species evenness) and remote-sensing data, this paper explores how hydrological fluctuations, microplastic and heavy metal contamination, and microbial shifts collectively influence ecosystem functioning. The findings indicate a measurable reduction in benthic macrofaunal diversity (by 38%), significant accumulation of microplastics (up to 3200 particles kg⁻¹ in southern sediments), and rising dominance of opportunistic microbial taxa linked to oil degradation. These trends demonstrate that the Caspian Sea’s biodiversity is under accelerating stress, demanding urgent implementation of adaptive management frameworks. Recommendations are proposed for conservation strategies integrating ecological monitoring, pollution mitigation, and climate adaptation at the regional scale. Keywords: Caspian Sea, biodiversity, pollution, microbial ecology, climate change, environmental stressors .