, 2010 and Stuart et al., 2013). Conversely, in some regions of the ocean where iron is replete, organisms can reduce their genetic

complement encoding iron scavenging siderophores, hence altering their functionality in a local context ( Patel et al., 2010). Temporal and spatial dimensions are intrinsically linked when considering biogeographic distributions of microorganisms. If an organism is not found in a particular location at the time of sampling it may be recovered if sampling depth is significantly increased (e.g. Caporaso et al., 2012b and Gibbons et al., 2013), or it may appear in a different season (e.g. Fuhrman et al., 2006). Long term monitoring has identified ecosystem shifts in the dominant community assemblages in the North Pacific subtropical gyre (Karl et al., 1995), whereby basin scale climatic events (in this case the El Niño southern Ibrutinib in vitro oscillation ENSO) led to a Dasatinib shift from a primarily nitrogen-limited to a primarily phosphorus-limited habitat with attendant changes in total and export production and in nutrient cycling pathways and rates. Seasonal cycling of communities (Fuhrman et al., 2006 and Gilbert et al., 2012), individual taxa, or distinct ecotypes of the same taxa is evident in many dynamic subtropical and temperate locations (e.g. Brown et al., 2005, Morris et al., 2005 and Carlson et

al., 2009). Polar regions, where the seasonal cycles are the longest in extent, and perhaps most physically dramatic, have rarely been sampled seasonally, and there is contrasting evidence for temporal cycling of organisms in the Arctic and Antarctic. While Antarctic waters display clear shifts between summer and winter communities (Grzymski et al., 2012 and Williams

et al., 2012), such an effect is not clear in the Arctic, where summer and winter communities examined in one study were not significantly different (Kirchman et al., 2010), and remained dominated by the same organisms. Over shorter time scales of days to weeks, bacterioplankton community composition does change but this change may not be “linear”. One Eulerian time-series study which examined daily shifts (~ 40 days) in community composition in a temperate marine environment ID-8 showed that communities tend to oscillate around a “mean”, so the rate of monthly change can be less than the rate of daily changes (Needham et al., 2013). These shifts in community composition over time are critical components to consider when examining global biogeography. Over global spatial scales, ecological patterns in beta-diversity for marine bacteria have been observed. Sometimes, but not always, these patterns are equivalent to those observed in macro-ecological studies. For instance, several studies have identified latitudinal gradients in the diversity of surface associated bacterial communities (Pommier et al., 2007 and Fuhrman et al., 2008). However, when the temporal diversity (i.e.