Mesozooplankton distribution near an active volcanic island in the Andaman Sea (Barren Island)

The study addresses the distribution and diversity of mesozooplankton near the active volcano-Barren Island (Andaman Sea) in the context of persistent volcanic signature and warm air pool existing for the last few months. Sampling was done from the stations along the west and east side of the volcano up to a depth of 1,000 m during the inter monsoon (April) of 2006. Existence of feeble warm air pool was noticed around the Island (Atm. Temp. 29°C). Sea surface temperature recorded as 29.9°C on the west and 29.6°C on the east side stations. High mesozooplankton biomass was observed in the study area than the earlier reports. High density and biomass observed in the surface layer decreased significantly to the deeper depths. Lack of correlation was observed between mesozooplankton biomass and density with chl. a . Twenty-three mesozooplankton taxa were observed with copepoda as the dominant taxa followed by chaetognatha. The relative abundance of chaetognatha considerably affected the copepod population density in the surface layer. A noticeable feature was the presence of cumaceans, a hyperbenthic fauna in the surface, mixed layer and thermocline layer on the western side station where the volcano discharges in to the sea. The dominant order of copepoda, the calanoida was represented by 52 species belonging to 17 families. The order poecilostomatoida also had a significant contribution. Copepods exhibited a clear difference in their distribution pattern in different depth layers. The families Calanidae and Pontellidae showed a clear dominance in the surface whereas small-sized copepods belonging to the families Clausocalanidae and Paracalanidae were observed as the predominant community in the mixed layer and thermocline layer depth. Families Metridinidae, Augaptilidae and Aetideidae were observed as dominant in deeper layers.