Effect of hydrodynamic conditions on seagrass ecosystems during Cyclone Lehar in the South Andaman Islands, India

The physical disturbances of hydrodynamic conditions in shaping the seagrass meadows were studied in the vicinity of seagrass meadows over the south of Port Blair in the An-daman and Nicobar Islands (ANI) during the lifetime of Cyclone Lehar using spatial and temporal metrological -oceanic parameters and in-situ measurements. A cyclonic depres-sion formed on 23 November 2013 over the west coast of the Malay Peninsula and then transformed into a severe cyclone named Lehar on 25th November 2013. It made its first landfall south of Port Blair in the ANI and caused extensive damage to life and properties. The present study made an attempt to investigate the hydrodynamic condition and their impact on the seagrass meadows during the lifetime of the cyclone. The results revealed that the floristic composition of seagrass species such as Thalassia hemperichii, Halodule pinnifolia and Halodule uninervis was badly damaged due to the effect of the high gra-dient of velocities in the vertical direction, turbulence, high energetic waves, and storm surge. Approximately 32.4% of the seagrass meadows were uprooted in Haddo Bay and 68% in Sesostris Bay of the South Andaman Islands. A year after the cyclone passage (De-cember 2014), 13% (-0.70 ha) of the seagrass meadow in Haddo Bay and 44.5% (-0.30 ha) of the seagrass in Sesostris Bay had recovered. This study emphasises that the mor-phometric features of the most dominant species, T. hemperichii, were regulated by the physical hydrodynamic mechanisms and led to substantial destruction in the study sites. This study is very useful to understand the impact of hydrodynamic conditions on seagrass ecosystems during a cyclone and brings attention to the real-time monitoring of seagrass ecosystems. Monitoring of the seagrass ecosystem can be further improved by predicting the behavioural dynamics of the marine ecosystem under the various scenarios of extreme weather conditions using high-resolution numerical models. It also helps to determine the appropriate management policy during extreme natural events.(c) 2022 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.