Microzooplankton concerning the plankton food web in subtropical frontal region of the Indian Ocean sector of Southern Ocean during austral summer 2012

Abstract The Southern Ocean is a very dynamic ecosystem comprising many fronts and zones. Among the fronts, the Subtropical Front (STF) is a region of high eddy activity exhibiting spatio-temporal variability. The variability of food web structure in such a dynamic system characterised by frequent eddy events and their influence on the plankton community structure is an interesting scenario to be addressed. The present study attempts to explain the variability of microzooplankton (MZP) mediation in the planktonic food web, using multi-disciplinary data collected along the zonal sections 40° S and 43° S in STF during the austral summer 2012. Even though, both the zonal sections are located in the STF, significant variability was observed in the thermo-haline structures of these two, due to the presence of multiple mesoscale features (viz. cyclonic and anticyclonic eddies), leading to discrete environments within STF. The study highlights the fact that the concept of the classical food web in productive environments (cyclonic eddies) is governed chiefly by the existence period of such dynamic events. On the contrary, in the generally less productive anticyclonic eddies, the variability of trophic level interaction vary between the periphery and core regions. The present study reveals the biological consequences of frequent mesoscale features in terms of the variability of food web structure. It elucidates the trophic importance of MZP in the two contrasting environments within the STF.