Abstract
In order to determine the influence of geographical distance, depth, and Longhurstian province on bacterial community composition and compare it with the composition of photosynthetic micro-eukaryote communities, 382 samples from a depth-resolved latitudinal transect (51°S–47°N) from the epipelagic zone of the Atlantic ocean were analyzed by Illumina amplicon sequencing. In the upper 100 m of the ocean, community similarity decreased toward the equator for 6000 km, but subsequently increased again, reaching similarity values of 40–60% for samples that were separated by ~12,000 km, resulting in a U-shaped distance-decay curve. We conclude that adaptation to local conditions can override the linear distance-decay relationship in the upper epipelagial of the Atlantic Ocean which is apparently not restrained by barriers to dispersal, since the same taxa were shared between the most distant communities. The six Longhurstian provinces covered by the transect were comprised of distinct microbial communities; ~30% of variation in community composition could be explained by province. Bacterial communities belonging to the deeper layer of the epipelagic zone (140–200 m) lacked a distance-decay relationship altogether and showed little provincialism. Interestingly, those biogeographical patterns were consistently found for bacteria from three different size fractions of the plankton with different taxonomic composition, indicating conserved underlying mechanisms. Analysis of the chloroplast 16S rRNA gene sequences revealed that phytoplankton composition was strongly correlated with both free-living and particle associated bacterial community composition (R between 0.51 and 0.62, p < 0.002). The data show that biogeographical patterns commonly found in macroecology do not hold for marine bacterioplankton, most likely because dispersal and evolution occur at drastically different rates in bacteria.
Highlights
Our understanding of marine bacterioplankton diversity and biogeography has been revolutionized by high-throughput sequencing in combination with extensive sampling efforts
We investigated the biogeography of marine bacteria using ribosomal sequence data of bacterioplankton communities in the photic zone across ∼12,000 km of the Atlantic Ocean
Our analysis suggests that the distancedecay relationship for marine bacterioplankton is dependent on the geographical scale that is analyzed, and there is no such relationship for the full transect
Summary
Our understanding of marine bacterioplankton diversity and biogeography has been revolutionized by high-throughput sequencing in combination with extensive sampling efforts. Community similarity decreases with increased geographical distance because of dispersal limitation and local adaptation (Nekola and White, 1999; Soininen et al, 2007a; Nemergut et al, 2013). Evidence for such a relationship in aquatic microbial communities is weak and controversial. The Tara Oceans expedition provides the largest and most complex metagenomics dataset of the marine bacterioplankton available to date (Sunagawa et al, 2015) It showed a weak decrease in bacterial community similarity with increasing distance between sampling sites, but only up to about 5000 km. Evidence is accumulating that bacterioplankton communities might follow a scale dependent distance-decay relationship
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