Impact of Monsoon Driven Cyclonic Storm <i>Daye</i> on Mesozooplankton Dynamics in Coastal Waters of the Bay of Bengal

ABSTRACT Variability in mesozooplankton (MZ) ecology and community structure in the Bay of Bengal (BoB) based on a meso‐scale process is presented during the summer monsoon (SM) of 2018. Cyclonic storm (CS) Daye impacted the northwestern BoB during this season. A coastal survey was conducted just after the cyclonic activity to investigate the impact of CS on the hydrography of coastal waters and the MZ species assemblage. The survey was conducted along eight transects representing a gradient of cyclonic impact from least to most affected by CS Daye . The northern transects (WBE and WBC) were least impacted, the central transects (ODP, ODR, and ODG) experienced moderate influence, and the southern transects (APB, APV, and APK) were highly impacted by the storm. There was a clear distinction in water quality and MZ community structure between the Northern and Southern transects. The Northern transects were characterized by high temperature, low salinity, low dissolved oxygen (DO), high nutrient concentration (except nitrate), high chlorophyll (Chl) a , high MZ biomass, and abundance. The opposite trend was noticed in the Southern transects. Gelatinous groups like Appendicularia, Ctenophora, Hydromedusae, and Thaliacea were present in high abundance in the Southern transects, while the Northern transects had a predominance of Copepoda. The Southern transects had a high predominance of Bestiolina similis , Euterpina acutifrons , Oithona brevicornis , and Salpa fusiformis , while the Northern transects had a dominance of Acartia ( Odontacartia ) spinicauda , Corycaeus crassiusculus , Undinula vulgaris , and Zonosagitta pulchra . A shift in the MZ community was recorded from Southern transects dominated by highly abundant cyclopoids and thaliaceans to Northern and Central transects characterized by predominantly calanoid species.