Ecological association between seagrass and mangrove ecosystems increases seagrass population longevity in island ecosystem

We report for first time about tropical seagrass meadows association with mangrove ecosystems and its effect on seagrass population dynamics off India in Andaman Sea. Two sites of Neil island, i.e. site 1, associated with mangroves and site 2 without mangroves were selected. Quadrat sampling (n=5) were used to collect sediment and seagrass samples. Reconstruction techniques were used to derive population age structure. T. hemprichii population was found mostly with sandy substrate at both sites, with silt consisting very low fraction at site 1. Density, biomass, productivity and morphometric features of T. hemprichii were significantly higher at site1. Reproductive density was higher at site 1, whereas reproductive effort to produce fruits were higher at site 2. The rhizome (vertical+ horizontal) production rates were higher at site 1 and the vertical elongation rate was higher at site 2. Plastochrome interval for site1 and 2 were 25.49 and 26.80 days respectively leading to formation of 14.31 and 13.62 leaves per year. T. hemprichii population at site 1 had four years of longevity and higher younger plants compared to site 2. The long-term average recruitment and present recruitment rate were higher at site 1 compared to site 2, resulting in steady state growth of the overall population at site 1. Higher number of younger plants suggests fitness of the T. hemprichii population at site 1, which increases the ecological significance of mangrove ecosystems have on seagrass population dynamics. This association should be considered for better management and conservation practices of coastal seascapes under global change scenarios.