Fig. 3.

A latitudinal gradient in marine epipelagic bacterial diversity. We calculated bacterial richness by using parametric methods implemented in the CatchAll program (44). Pearson correlation r values were between natural log-transformed estimated richness values and absolute latitudes. A similar correlation was obtained with richness estimation with normalized datasets (subsampling to minimum numbers of reads). Our correlation values between latitude and estimated richness were also similar to those from previous amplified ribosomal intergenic spacer analysis results (23) with 100 data points at 57 locations (Pearson r = −0.422).