Diversity follows a highly significant seasonal fluctuation which results in an “inverse-latitudinal gradient” with peak diversity occurring at temperate latitudes during winter months,
hence alternating between north and south over the year (Ladau et al., 2013), a pattern which is different from that displayed by most macroorganisms. Zinger et al. (2014) reported taxa–area values (the slope of the increase in the number of taxa observed when examining increasingly larger area) for surface marine bacteria at magnitudes consistent with those observed for macroorganisms, while distance decay relationships (the slope of the increasing dissimilarity of taxonomic composition between NU7441 samples taken over increasing geographic distances) derived
from the same sample dataset were much smaller than those reported for macroorganisms. Overall, however, the existence of these and other beta-diversity patterns, such as the Rapoport effect, whereby Selleck Ceritinib bacterial latitudinal ranges are narrower than expected by chance (Amend et al., 2012), suggest that marine bacteria are, at least to some extent, dispersal limited (Zinger et al., 2014). However, many of these global studies have used the same ICoMM dataset and because of the logistical difficulties in sampling high latitude waters in the winter these observations are spatio-temporally limited. Half the PTK6 primary production of the ocean occurs in the narrow photic zone layer that extends to approximately 200 m depth and is seasonally either present or absent at the poles. Primary producers in the photic zone include both picocyanobacteria and photosynthetic eukaryotes of which diatoms account for 40% of annual primary production (Falkowski and Raven, 2008). The distributions of primary producers are governed in part by their
relative size and nutritional status of the oceanic provinces. Smaller cells have a greater capacity for uptake of nutrients via diffusion, leading to competitive exclusion of larger cells in nutrient limited conditions, such as the oligotrophic open ocean (Chisholm, 1992 and Raven, 1999). Hence the picocyanobacteria, predominantly the genera Synechococcus and Prochlorococcus, dominate the oligotrophic open ocean environment but are outcompeted by fast growing photosynthetic picoeukaryotes (PPE) in the nutrient rich higher latitudes ( Zubkov et al., 2003). Indeed there is a systematic increase in the ratio of PPE/picocyanobacteria with increasing latitude and decreasing temperature ( Bouman et al., 2012). Further, nutrient ratios govern the distribution patterns of photosynthetic eukaryotes such as Prymnesiophyceae and Chrysophyceae. Prymnesiophyceae abundances peak in waters with a high (25:1) nitrogen:phosphate (N:P) ratio, while Chrysophyceae peak in waters with low (12:1) N:P ( Kirkham et al., 2013).