Microbial processes in cold oceans .1. Relationship between temperature and bacterial growth rate

Despite the obvious relevance of the high latitude oceans to models and budgets of biogenic carbon, the seasonal patterns of energy flow through the lower food web in this region are poorly understood. It has been suggested that, in high latitude and cold oceans, the rates of bacterial metabolism and growth are low and are depressed to a much greater degree than those of co-occurring phytoplankton and metazoan heterotrophs. The low-temperature suppression of bacterial growth would reduce microbial food web activity, bacteria would consume and recycle less primary production and more phytoplankton carbon would be available to metazoan grazers. The implications of this scenario for models of oceanic carbon flow are profound. In this paper, we present an analysis of 66 published studies on temperature and growth rate for bacteria from 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)) and 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 significantly different. For both the published data as well as for the field study in Conception Bay, Newfoundland, the SGR was significantly greater (p < 0.01) when computed from empirical thymidine conversion factors than from theoretical or literature derived thymidine conversion factors. 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 compute growth. We propose that bacteria-based food webs and microbial trophic pathways are as important in overall energy and material cycling in high latitude oceans as they are at lower latitudes.