Variability in the zooplankton assemblages in relation to environmental variables in the tidal creeks of Sundarbans estuarine system, India.

The present study illustrates a holistic account of zooplankton community dynamics in relation to physicochemical variables in the tidal creeks of Indian Sundarbans estuarine system. Eleven water variables and zooplankton samples were collected in a monthly basis from the six sampling locations between July 2016 and June 2018. Out of the 11 water parameters, seven parameters (temperature, salinity, dissolved oxygen, turbidity, PO4 - P, NO3 - N, and NO2 - N) varied significantly (p ≤ 0.05) among seasons. A total of 63 zooplankton taxa were recorded with the predominance of Copepoda. Permutational multivariate analysis of variance (PERMANOVA) depicted the significant variations of zooplankton population both spatially (F = 2.313; p = 0.001) and temporally (F = 6.107; p = 0.001). Out of the 41 species of Copepoda recorded, 14 species (Paracalanus parvus, Parvocalanus dubia, Bestiolina similis, Acrocalanus gibber, A. gracilis, Acartia erythraea, A. spinicauda, Pseudodiaptomus serricaudatus, P. annandalei, P. aurivilli, Oithona brevicornis, O. similis, Longipedia weberi and Microsetella norvegica) were indicated as "characterizing species" in the creek environment, which highlighted the euryhaline nature as well as broad range of thermal tolerance of these species. Acrocalanus longicornis, Eucalanus crassus, Candacia bradyi, and Acartia sewelli were specifically found in pre-monsoon; Euterpina acutiformis, Clytemnestrata rostrata, Acartia plumosa, and Canthocalanus pauper were specific to post-monsoon season, whereas Mesocyclops leuckarti, Temora turbinata, and Temora discaudata were found only during monsoon. Thus, it explains the limited period of existence, highlighting the temporal shift in species abundance in the creeks. Overall, the calculated mean value of α-diversity (d' = 4.07; H' = 2.31) indicated a "good" zooplankton diversity in the creeks. The biota-environmental relationship following canonical correspondence analysis revealed that variables, viz., water temperature, turbidity, and NO3 - N, were the explanatory variables during monsoon; pH and DO in post-monsoon; PO4 - P, SiO4 - Si, and salinity in pre-monsoon that explained the variations of zooplankton community compositions in the creeks. The variables (PO4 - P, NO3 - N, and SiO4 - Si) that are correlated to the zooplankton community implied their indirect effect on the distribution of zooplankton by supporting the phytoplankton succession and production in the mangrove-dominated creeks.