Ecology of seagrass associated fin fishes and conservation perspectives of seagrass ecosystem in Palk Bay and Gulf of Mannar, Tamilnadu

Abstract

Seagrass meadows are among the most productive and ecologically significant coastal ecosystems that sustain marine biodiversity and human health as well. Seagrass meadows are particularly well-structured and provide habitat for many marine organisms. Their interaction with coral reefs, estuaries and coastal waters contributes to the functioning of whole seascapes. In addition to providing habitat, seagrass meadows are important for fisheries, protect coasts, stabilize sediment, and sustain millions of coast benefits, seagrass ecosystems are in decline worldwide, which is a direct consequence of increasing anthropogenic pressures and their ability to sustain biodiversity and ecosystem services. In India, Palk Bay and the Gulf of Mannar are among the most extensive and diverse seagrass meadows and are ecologically unique areas where biodiversity conservation and fisheries sustainability are linked. These ecosystems support threatened species such as the dugong and provide important fishing sites for coastal communities. But over time, fishing pressure, habitat degradation and other human-induced disturbances have made it hard to sustain them in the long term. Although research has been done on the distribution and composition of Indian seagrass meadows, the ecological processes that underlie the functioning of fish and ecosystems are poorly understood. The current study aimed to fill these knowledge gaps by integrating the assessment of commercially important finfish diversity, resource partitioning, ecosystem services and anthropogenic threats into a single ecological framework with following objectives: 1. Assess the commercially important fin fish species associated with seagrass ecosystems in Palk Bay. 2. Document the resource (food and space) partitioning patterns among fin fish species associated with seagrass ecosystems 3. valuate ecosystem services provided by seagrass ecosystem with reference to commercial fin fish fishery 4. Assess major threat posed by different fishing practices in seagrass ecosystem and provide option for conserving seagrass ecosystems. Rather than focusing on these aspects in isolation, I investigated how they interact and contribute to the healthy functioning and resilience of seagrass ecosystems. Fish diversity, habitat complexity, ecological connectivity and ecosystem services are linked and it is suggested that disturbances affecting one component can affect the health and sustainability of the whole system. Thus, the synthesis in this chapter synthesizes the findings of the study and considers their relevance in the management of fisheries and biodiversity conservation and the sustainable management of seagrass ecosystems in Palk Bay and the Gulf of Mannar. 1. Commercially Important Finfish Species Associated with Seagrass Meadows The first objective of the present study was to assess the commercially important finfish species associated with seagrass ecosystems of Palk Bay and the Gulf of Mannar and to understand the ecological factors influencing their distribution and habitat use. Although seagrass ecosystems are widely recognized as important fish habitats, information on commercially important finfish species associated with Indian seagrass meadows has remained limited. This investigation was therefore undertaken to document fish diversity, evaluate regional variation in fish assemblages, and examine the relationship between habitat characteristics and fish communities. A combination of fish market surveys and underwater visual census techniques was employed to obtain a comprehensive understanding of seagrass-associated finfish diversity. Prior to ecological assessments, a comparison between belt transects and point count methods was carried out to standardize the sampling protocol. Both methods produced similar estimates of species diversity and evenness, but point counts recorded higher guild-wise fish densities and provided better opportunities for behavioural observations and size-class assessments. Based on these observations, point counts were adopted as the standard method for subsequent underwater surveys. Fish market surveys conducted across the major landing entres of Palk Bay confirmed that seagrass ecosystems support a large number of commercially important fish species. A total of 161 fish species belonging to 58 families were found to be consistently associated with seagrass fishing grounds. Considerable variation was observed among fish markets, with larger landing centres recording greater species and family richness. These observations indicate that seagrass ecosystems contribute substantially to local fisheries and support a diverse range of economically valuable species. Underwater visual surveys further demonstrated the ecological importance of seagrass meadows. A total of 85 fish species representing 51 genera and 31 families were recorded during field observations. The Gulf of Mannar supported greater species richness and diversity than Palk Bay, while Palk Bay exhibited higher species dominance. Family-wise composition also differed between the two regions, with reef-associated families being more abundant in the Gulf of Mannar and estuarine and shallow-water associated families showing greater representation in Palk Bay. These differences suggest that local habitat characteristics and connectivity with surrounding ecosystems strongly influence fish assemblages.