Monsoonal estuaries, located along the coastline of the Indian subcontinent, differ from other estuaries by their time dependence on the salinity characteristics. Effective sustenance and retention of the mesozooplankton community in the estuarine habitats is often determined by their dominant behavioral patterns: diel vertical migration (DVM) and tidal vertical migration (TVM). The modes of these endogenous rhythms often vary among estuaries based on the river runoff and tidal characteristics. The present study is a pioneering attempt to depict the vertical migration pattern of zooplankton along a diel and tidal scale in a tropical, microtidal, monsoonal estuary. We observed that in spite of the prominent asymmetry in the magnitude of the river runoff between the seasons, most of the zooplankton groups exhibited strong DVM, with a clear increase in biomass and abundance in surface waters during night. The peak increase in biomass and abundance at night always synchronized with the slack periods in the tidal cycles, which differed from the general concepts of downward migration during ebb tide and upward migration during flood tide in estuarine systems. The weak currents during the slack period might have favored the effective vertical migration of the mesozooplankton community in this monsoonal estuarine system. © 2015 Society of Wetland Scientists
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors thank Director, CSIR-National Institute of Oceanography, India for facilities and encouragement. We thank all NIO staff who helped in carrying out the simultaneous time series measurements in Cochin backwaters. The authors thank ICMAM-PD Chennai for the financial support. This work forms a part of the Supra Institutional Project (SIP) 1302 of NIO and Grant-in-Aid project 'Ecosystem modeling of Cochin backwaters' funded by ICMAM - PD Chennai. The first author is thankful to CSIR for the award of Senior Research Fellowship. This is NIO contribution number 5725.