Distribution and diversity of benthic macroinvertebrates in stream-associated Myristica swamp forests of the southern Western Ghats, India

Myristica swamp forests are globally rare tropical freshwater forest wetlands whose hydrologically diverse aquatic habitats remain poorly studied, particularly with respect to benthic macroinvertebrate communities and their environmental drivers. This study investigated the taxonomic composition, diversity, seasonal variation, and environmental drivers of benthic macroinvertebrate assemblages in stream-associated aquatic habitats of selected Myristica swamp forests in the southern Western Ghats, India. A total of 124 benthic macroinvertebrate taxa belonging to three phyla, four classes, 12 orders, and 60 families were recorded from eleven sampling sites during the pre-monsoon, monsoon, and post-monsoon seasons (2021–2023). Odonata constituted the dominant order. The number of individuals collected per standardized sample was highest during the pre-monsoon season, followed by the post-monsoon and monsoon seasons. Diversity indices indicated consistently high taxonomic diversity, high evenness, and low dominance across the study sites, reflecting a well-structured benthic community. Canonical Correspondence Analysis explained 81.2% of the variation in community composition and identified gradients of organic enrichment, sediment characteristics, oxygen availability, and ionic composition as the principal environmental drivers structuring macroinvertebrate assemblages. Pollution-sensitive taxa, particularly Ephemeroptera, Plecoptera, Trichoptera, and Odonata, were associated with well-oxygenated and structurally complex habitats, whereas tolerant taxa, including Naididae, Tubificidae, and Chironomidae, were associated with organically enriched sediments and mineral-rich conditions. Pearson correlation analysis further demonstrated strong relationships among hydrological, sediment, and water-quality variables, highlighting the importance of seasonal environmental dynamics in shaping benthic assemblages. These findings provide one of the first comprehensive ecological assessments of benthic macroinvertebrate communities inhabiting Myristica swamp forests of the southern Western Ghats and establish an important baseline for biomonitoring and conservation of these globally significant freshwater forest wetlands.