Phytoplankton standing stocks in relation to krill in Antarctic waters

Investigations on krill trawl operations in the southern ocean were accompanied by the phytoplankton and zooplankton studies during the First Indian Antarctic Krill Expedition. The study area which lies between latitude 56° to 61° 17's and longitude 30° to 40°E is characterized by cold surface waters with temperature ranging from 0 to 3° C and high nutrient content. Phytoplankton cell counts in surface waters ranged from (1.92 to 21.89) x l04 cells/litre. Phytoplankton cells represented 33 species, consisting of 32 diatoms and one dinoflagellete. Chaetoceros and Nitzschia spp. dominated the phytoplankton organisms. The other common diatoms present during the studies were Navicula, Rhizosolenia, Leptocylindrus and Corethron criophilum. Calm sea state prevailing from 27 January to 11 February favoured proliferation of certain phytoplankton species to bloom condition.
Zooplankton biomass showed wide fluctuation, with values ranging from 9.8 to 303.7m1/100m3. While the total catch per (IKMT) trawl ranged from 0.2 to 2400 kg, the percentage of kill occurrence varied from 0 to 100% at stations sampled. The fluctuations in phytoplankton and zooplankton standing stocks followed a similar trend. Marked drop in phytoplankton and zooplankton in the region of krill swarm however showed active feeding by the latter on these planktonic communities. The results indicate that areas favouring phytoplankton blooms and zooplankton abundance could be possible sites for locating krill fisheries in the southern oceans.