Impact of the tropical cyclonic storm ‘Aila’ on the water quality characteristics and mesozooplankton community structure of Sundarban mangrove wetland, India

Abstract

Present study examine the changes in the occurrence and composition of mesozooplankton (0.2 – 20 mm body size) in the context of water quality parameters at three stations of Sundarban coastal region, West Bengal due to the

odious event of severe tropical cyclonic storm ‘Aila’ on 25^th May, 2009. The Aila incident not only caused stupendous changes in the physicochemical characteristics of the water but also left direct impact on the mesozooplankton biomass. A sharp increment in water turbidity, chemical oxygen demand (COD), phytopigment chlorophyll b (chl b) and micronutrients (nitrate, phosphate and silicate) were noticed during post-Aila period with a corresponding decrease of water transparency and phytopigments chl a and chl c. Reduction of zooplankton biomass, density and species diversity was also pronounced during post-Aila period. An absolute dominance of two copepod species of diverse feeding guilds, namely, <i>Bestiolina similis </i>(herbivore) and <i>Oithona brevicornis </i>(carnivore) was the most interesting feature observed during post-Aila period. The meroplanktons such as nauplius, zoea and ichthyoplanktons which constituted the most dominant forms (~31 % of total mesozooplankton) during pre-Aila period, were completely absent in post-Aila stage.