Bacterial epibiont communities of panmictic Antarctic krill are spatially structured

Abstract Antarctic krill ( Euphausia superba ) are amongst the most abundant animals on Earth, with a circumpolar distribution in Southern Ocean. Genetic and genomic studies have failed to detect any population structure for species, suggesting single panmictic population. However, hyper‐abundance of slows rate genetic differentiation, masking potential underlying structure. Here we use high‐throughput sequencing bacterial 16S rRNA genes show that epibiont communities exhibit spatial structuring, driven mainly by distance rather than environmental factors, especially strongly krill‐associated bacteria. Estimating ecological processes driving community turnover indicated this was dispersal limitation increasing geographic distance. Furthermore, divergent generated from swarm split between aquarium tanks under near‐identical conditions suggests physical isolation itself can cause diverge. Our findings geographically structured, direct contrast lack observed data.