Nudibranchia At The Edge: Benthic Diversity Across The Aquatic Habitats In Thoothukudi Coast, Gulf Of Mannar, Tamilnadu, India

Abstract

Nudibranchs, a diverse group of benthic mollusks belonging to the subclass Nudibranchia, are increasingly recognized as sensitive bioindicators of aquatic ecosystem health. This study investigates the benthic diversity and ecological distribution of Nudibranchia across three distinct aquatic systems—coral reefs, mangroves and freshwater beds—within the coastal region of Thoothukudi, Tamil Nadu. Comprehensive field surveys and underwater visual censuses were conducted over a period of six months, accompanied by habitat characterization and water quality assessments. Species were identified based on morphological features and, where necessary, confirmed through molecular barcoding.

The study revealed a surprising richness of nudibranch species across all habitats, with the highest diversity found in coral reef ecosystems, followed by mangroves and then freshwater environments. Coral reefs supported a wide array of dorid and aeolid forms, while the mangrove-rooted zones revealed cryptic and camouflaged species, showcasing niche-specific adaptations. Freshwater occurrences, though rare, underscore the tolerance and possible range expansion of certain euryhaline taxa. Our findings highlight the ecological significance of Nudibranchia in benthic food webs and their vulnerability to environmental perturbations, such as coastal development, pollution and climate-induced stressors. The study not only expands the regional checklist of nudibranchs in South India but also underscores the importance of conserving benthic habitats in Thoothukudi. Further integrative studies combining taxonomy, genetics and habitat modelling are recommended to monitor shifts in benthic biodiversity and to inform conservation strategies in this ecologically vital region.