Seagrass meadows form important habitats in the lagoons of the Lakshadweep archipelago in the Indian ocean. Since 2005 fishers have been reporting declines in seagrass cover due to overgrazing by green sea turtles. Apart from being important conservation flagships, green turtles are strong ecosystem interactors, and can potentially cause trophic cascades or functional extinction of seagrass ecosystems. Fishers also reported decline in baitfish and reef fish catches due to declines in seagrass cover. We have been monitoring interactions between turtles and seagrasses in the lagoons to understand the impact of turtle herbivory. Over the years, we have expanded our monitoring to 5 islands, as turtles moved across the archipelago. Lagoons in the Lakshadweep archipelago showed distinct patterns of increase in turtle densities followed by radical biomass reduction and compositional shifts in seagrass meadows, leading to functional extinction of seagrass. Turtle overgrazing resulted in massive declines in seagrass dependent fish diversity, biomass, and abundance, and major reductions in sediment-stored carbon.
We continue to monitor the movement of green sea turtles and the compositional and functional changes in seagrass meadows. More recently we have set up ‘seagrass insurance’ sites in the lagoons of several islands.
Through this work, we hope to understand the functional recovery of seagrass.