Summary of Abstract Submission

Abstract Submission No. IO50-09-0072PresentationPoster

DIEL VARIATION IN SURFACE ZOOPLANKTON ABUNDANCE, BIOMASS AND COMMUNITY STRUCTURE IN THE SOUTH WESTERN TROPICAL INDIAN OCEAN DURING JUNE 2014

V. Venkataramana*1, S. C. Tripathy2, N. Anilkumar1

1 ESSO-National Centre for Antarctic and Ocean Research, Goa, India
2 , India

ABSTRACT :

Time series (@6 h intervals over 4 days) assessments of surface zooplankton abundance, biomass and community composition were carried out in the south-west tropical Indian Ocean (SWTIO) during south-west monsoon (June) of 2014. Zooplankton biomass and density varied between 1.34 - 9.35 ml 100 m-3 and 2576 ┐ 28764 N 100 m-3, respectively and showed clear diel variation being lower during daytime (2.71▒0.23 ml 100 m-3 and 5814▒1659 N 100 m-3) and higher during night (6.40 ▒ 1.69 ml 100 m-3 and 13460 ▒ 5495 N 100 m-3). Sharp increase and decrease of zooplankton biomass was observed at dusk and dawn, respectively indicating the influence of incident light on vertical migration of zooplankton. Copepods were the most dominant taxon comprising 90% of the total zooplankton density followed by chaetognatha (7%), appendicularia (2%) and decapoda (1%). Among the copepods, poecilostomatoida was the most abundant followed by calanoida, cyclopoida and harpacticoida. Altogether, 55 species occurred in the pelagic realm of which 47 species were fairly ubiquitous from copepod group. Highest species diversity was observed during the night as some of the species (Paracalanus parvus, Centropages gracilis, Oithona setigera and Microsetella norvegica) depicted significant diel changes by appearing only at night. Phytoplankton biomass which varied between 0.1 ┐ 0.18 mg m-3 had higher contribution from pico-phytoplankton (>0.2Ám) than micro-phytoplankton (>10Ám). Unlike micro-phytoplankton clear diurnal variation was observed in case of pico-phytoplankton. Diel variation of phytoplankton biomass and zooplankton biomass showed opposite trend in the study area.