Warmer temperatures favor slower-growing bacteria in natural marine communities

Earth’s life-sustaining oceans harbor diverse bacterial communities that display varying composition across time and space. While particular patterns of variation have been linked to a range of factors, unifying rules are lacking, preventing the prediction of future changes. Here, analyzing the distribution of fast- and slow-growing bacteria in ocean datasets spanning seasons, latitude, and depth, we show that higher seawater temperatures universally favor slower-growing taxa, in agreement with theoretical predictions of how temperature-dependent growth rates differentially modulate the impact of mortality on species abundances. Changes in bacterial community structure promoted by temperature are independent of variations in nutrients along spatial and temporal gradients. Our results help explain why slow growers dominate at the ocean surface, during summer, and near the tropics and provide a framework to understand how bacterial communities will change in a warmer world., To explore the distribution of bacterial life strategies along principal axes of temperature variation in the ocean, we gathered 16S rRNA gene amplicon sequencing datasets of marine bacterial communities encompassing wide seasonal, latitudinal, and depth gradients.
We focused on three particular datasets in the main text to represent the three principal axes of temperature variation in free-living bacterial communities (Fig. 1a). First, to analyze seasonal data, we used an eight-year pelagic microbial time series from the Linnaeus Microbial Observatory (LMO) in the Baltic Sea, 11 km off the northeast coast of Öland (N 56°55.8540′, E 17°3.6420′) (green dot in Fig. 1a). Seawater samples have been collected since 2011 on a monthly to weekly basis, together with environmental variables like temperature, inorganic nutrients (nitrate, phosphate and ammonium), dissolved organic carbon (DOC), and chlorophyll a concentrations (fig. S7). The LMO dataset includes free-living (<3 m and >0.2 m...,