Diel vertical migration of zooplankton in Andaman Sea

Abstract

Several groups of zooplankton exhibit Diel Vertical Migration (DVM), during which, hours of darkness are spent near the surface of the water and the day light hours at deeper depths. Though many earlier workers have worked on the DVM all several regions of the world, the phenomenon is said to poorly understood. Andaman Sea is partially isolated part of north eastern Indian Ocean, occupies 6.6 x 103 km3 with an average depth of 1096M, is connected to Bay of Bengal by numerous channels. It is oligotrophic in nature with rich in marine wealth and hence, attracted many researchers and several cruises in this area, dating back from 1869 lead by Francis Day. Inspite of this, due to poor sampling, not much is known either about the diversity or DVM of zooplankton in this area. Therefore an attempt has been made to study the DVM at Andaman Sea. ORV Sagar Kenya was made to station at a particular place and 12 samplings of 3 replicates each at an interval of two hours for entire diel cycle was conducted, by using Bongo net. The samples were collected from 30-OM depth. They were subjected for analysis for biomass, wet weight, species composition, species diversity, patchiness, evenness fluctuation and later the data obtained thus was subjected for cluster analysis (Similarity matrix method) and dendrograms were prepared to compare the similarity index with the time of sampling. The results obtained are discussed in the light of available literature.