MICROBIAL PROCESSES IN COLD OCEANS .1. RELATIONSHIP BETWEEN TEMPERATURE AND BACTERIAL-GROWTH RATE

Despite the obvious relevance of the high latitude oceans to models an d budgets of biogenic carbon, the seasonal patterns of energy flow thr ough the lower food web in this region are poorly understood. It has b een suggested that, in high latitude and cold oceans, the rates of bac terial metabolism and growth are low and are depressed to a much great er degree than those of co-occurring phytoplankton and metazoan hetero trophs. The low-temperature suppression of bacterial growth would redu ce microbial food web activity, bacteria would consume and recycle les s primary production and more phytoplankton carbon would be available to metazoan grazers. The implications of this scenario for models of o ceanic carbon flow are profound. In this paper, we present an analysis of 66 published studies on temperature and growth rate for bacteria f rom the World Ocean, including polar regions, and examine the results of a field investigation of bacterioplankton growth in seasonally cold Newfoundland (eastern Canada) coastal waters. Based upon the analysis of published data, where approximately 50 % of the observations were from environments less than or equal to 4 degrees C, we report a weak (r(2) - 0.058, n = 231) relationship between specific growth rate (SGR ) and temperature with a Q(10) = 1.5. The mean (0.39 to 0.41 d(-1)) an d median (0.25 to 0.29 d(-1)) SGR of bacteria from cold (less than or equal to 4 degrees C) and warm (>4 degrees C) waters were not signific antly different. For both the published data as well as for the field study in Conception Bay, Newfoundland, the SGR was significantly great er (p < 0.01) when computed from empirical thymidine conversion factor s than from theoretical or literature derived thymidine conversion fac tors. Our analysis suggests that the growth rates of bacterioplankton from cold and temperate oceans are similar at their respective ambient temperatures, when the appropriate conversion factors are used to com pute growth. We propose that bacteria-based food webs and microbial tr ophic pathways are as important in overall energy and material cycling in high latitude oceans as they are at lower latitudes.