Are bacteria active in the cold pelagic ecosystem of the Barents Sea?

Abstract

Bacterial biomass and activity indicators have been studied at low water temperatures (-1.9 to +4°C) in Barents Sea. Strong responses by indicators of bacterial activity, such as hydrolytic enzyme and substrate uptake potentials, were observed in association with the development of phytoplankton blooms. At late successional stages of blooms, observation by epifluorescence microscopy revealed heavy bacterial colonisation of detrital matter, in particular of senescent colonies of Phaeocystis pouchetii. Based on the retention of bacteria on filters of 1 μm pore size, up to 55% of the bacterial population was estimated to be attached to organic aggregates in some cases. Based on thymidine incorporation and a conventional conversion factor, bacterial generation times as short as one day were estimated at temperatures below zero. Changes in substrate availability governed by the successional stages of the planktonic ecosystem seem to be more important as controlling factors for bacterial growth than the low temperatures of the Barents Sea.