Zooplankton in relation to hydrography and pelagic fisheries in the inshore waters of Vizhinjam, Trivandrum

Abstract

The seasonal fluctuations in the total plankton biomass and in the abundance of major zooplankters in the Vizhinjam Bay and the adjacent open sea were studied for two years from February 1980 to January 1982 in relation to the hydrography and the pelagic fisheries of the region. Copepods formed the major component of the zooplankton community for the greater part of the year. The other dominant groups were decapod larvae, cladocerans and chaetognaths. During certain months copepods were outnumbered by cladocerans, which swarmed during monsoon months only. Decapod larvae, appendicularians, fish eggs, fish larvae and Lucifer exhibited a sharp decline during south-west monsoon period. The revival started with the north-east monsoon and these groups attained their peak abundance in different months. The total zooplankton volume did not exhibit significant relationship with any of the hydrographic parameters investigated. The peak periods in the zooplankton biomass were found to coincide with the peak seasons of pelagic fisheries in both the years of collection. The importance of zooplankters in the study of the pelagic ecosystem in general and the fisheries in particular is pointed out.