Ecological Distribution and Trophic Dynamics of Carnivorous Fishes across Salinity Gradient in Ashtamudi Lake, Southwest India

Abstract

Ashtamudi Lake is a Ramsar-designated protected estuarine ecosystem where salinity levels strongly influence which species live in different areas. This study investigated the distribution and feeding ecology of 20 carnivorous fish species out of 97 total fish species found across three sites with different salinity levels. Species richness (S=28) was highest at the Kidapram site, a freshwater transition zone, highlighting its importance as a diverse habitat. Indicator Species Analysis identified key species like Dussumieria acuta and Liza parsia that showed strong preferences for specific transition zone habitats, indicating good habitat quality. Food web analysis revealed complex feeding relationships connecting bottom-dwelling organisms with surface water species. Large carnivorous fish such as Sphyraena jello and Caranx ignobilis play important roles in controlling the food web. Indicator Species Analysis (ISA) identified several taxa with strong site fidelity and significant indicator values. Notably, Dussumieria acuta (IndVal = 0.81), Sardinella fimbriata (0.79), Ehirava fluviatilis (0.75), and Liza parsia (0.69) showed high associations with specific ecosites, underscoring their potential as bioindicators for environmental monitoring. Energy flow through the system varies seasonally, with zooplankton populations peaking during the monsoon season at Kidapram, providing a major seasonal food source. Additionally, planktivorous fish selectively feed on certain zooplankton sizes, which changes the zooplankton community structure. These results show that carnivorous fish communities are shaped primarily by habitat variety, salinity gradients, and food availability. This information is essential for monitoring and managing this important tropical coastal ecosystem sustainably.