Boat anchors not OK: Loss of Dugong grass (Halophila ovalis) population structure in Havelock island of Andaman and Nicobar Islands, India

Abstract

Anthropogenic disturbance due to deployment of boat anchors and loss of seagrass ecosystem is not well understood in India. So, we used Govind Nagar beach of Havelock Island of Andaman and Nicobar Islands (ANI)to assess the impacts of boat anchors from traditional fishing and recreational activities on the seagrass Halophila ovalis population structure. H. ovalis density, biomass, morphometrics, canopy height and percentage cover were estimated from two stations of Govind Nagar beach i.e., one highly impacted from boat anchors (Station1) and a sheltered station (Station 2). A clear evidence in reduction of shoot density of H. ovalis was observed at station 1, exception was similar apex densities between both stations. H. ovalis morphometrics, such as number of leaves per shoot, leaf length, width and horizontal rhizome length were observed with significant lower values at station 1 compared to the sheltered station 2. Reduction in seagrass morphometrics also resulted in the loss of seagrass canopy height and percentage cover. A clear evidence of loss of seagrass population structure under the influence of physical disturbances caused by boat anchors were observed. We report for the first time the impacts of boat anchors on seagrass ecosystems of India and our results pitch for wider studies across India. The impact of boat anchors is small-scale, but in long-term loss of seagrass ecosystem services will have dire consequences on fish habitat and carbon storage. Therefore, proper management and conservation measures should be taken to prevent the loss of important dugong grass habitats of ANI. Highlights Physical disturbances caused by boat anchors decreased the shoot density of H. ovalis by 1.2-fold. 1 to 2-fold reduction in canopy height and the morphological features of individual plants were observed due to damage caused by boat anchors Habitat disturbance reduced 1.6-fold percentage cover of H. ovalis at Havelock Island of Andaman and Nicobar Islands, India