Response of polar front phytoplankton and bacterial community to micronutrient amendments

Abstract

In a shipboard microcosm experiment we manipulated cobalt (Co), copper (Cu), iron (Fe), and Fe+Co availability in surface water samples collected during austral summer of 2013 from a Polar front (PF) location in the Indian Sector of Southern Ocean, to examine the responses of phytoplankton as well as bacterial community (BC) to these micronutrient amendments. Total chlorophyll a (Chl a) concentration increased significantly (P<0.01) in all micronutrient-enriched microcosms (MEM), with the incubation period unlike in the control microcosms (CM). Bacterial abundance in Co, Fe and Fe+Co-enriched microcosms increased 1.5 fold within 5 days of incubation, unlike in other microcosms. Despite significant increase in Chl a, the DGGE banding pattern reflects minor differences in the BC. However, there were significant differences in relative abundance (i.e band intensity) of two most responsive phylotypes identified as Rhodospirillales and Rosebacter sp of Alphaproteobacteria group between MEM and CM. Strong correlation was not discernable between Chl a concentration and bacterial abundance as well as BC structure. Apparently autotrophic processes in this region are not only limited by the availability of Fe, but also Co and Cu.