Summary of Abstract Submission

Abstract Submission No. IO50-09-0061PresentationPoster

PHYTOPLANKTON SIZE DISTRIBUTION AND COMPOSITION IN THE SOUTHEASTERN ARABIAN SEA: CHEMTAX ANALYSES

Keerthi Suman*1, G.V.M.Gupta1, D.V.Subba Rao2, Anilkumar Vijayan1, M.Sudhakar1

1 Centre for Marine Living Resources and Ecology, India
2 University of New Mexico, USA

ABSTRACT :

We present results on HPLC based pelagic-sediment coupled phytoplankton pigments in the shelf (50 m) and offshore (1000 m, pelagic only) regions from seven transects between Mangalore (1.2.8N) and Trivandrum (8.5N) along the southeastern Arabian Sea during oligotrophic fall inter-monsoon (October 2014). The estimated sixteen pigments were grouped into pico (< 2 μm), nano (<20 μm) and micro (>20 μm) size fractions and subjected to CHEMTAX analysis to determine the relative contribution of the main taxonomic groups to total phytoplankton biomass. Chlorophyll a was the most abundant of all pigments followed by fucoxanthin. Pico: nano ratios (0.96-2.15) suggest that in all the shelf waters, except Mangalore, picoplankton distribution was conservative. Shelf waters of Mangalore had predominantly encountered with micro (66%) and nano (33%) fractions due to diatom-dinoflagellate (Red Noctiluca) bloom. Picoplankton was the most dominant fraction (45-87%) in all the offshore stations, its dominance shifted from Prymnesiophytes in the south to diatom-dominated microplankton towards the north. This is supported by a complete absence of microplankton in the southern offshore stations (8.5 to 10N). Major sediment pigments are in the order of Bacillariophyceae>Dinophyceae>Cryptophytes>Cyanophyceae. Sediment chlorophyll: phaeopigment ratios (0 to 0.08) showed intense degradation of settled plankton and fecal pellets from the previous high productive upwelling summer monsoon (June-September). Notably, sediment chlorophyll b is absent at all stations perhaps due to its preferential degradation. Our HPLC results and CHEMTAX are in consonance with phytoplankton size-classes and yielded high correlation (P<0.001) between chlorophyll and diagnostic pigments.