Oceanic Microplankton Do Not Adhere to the Latitudinal Diversity Gradient

A latitudinal biodiversity gradient has captivated ecologists for years, and has become a widely recognized pattern in biogeography, manifest as an increase in biodiversity from the poles to the tropics. Oceanographers have attempted to discern whether these distribution patterns are shared with marine biota, and a lively debate has emerged concerning the global distribution of microbes. Limitations in sampling resolution for such large-scale assessments have often prohibited definitive conclusions. We evaluated microbial planktonic communities along a ~ 15,400-km Pacific Ocean transect with DNA from samples acquired every 2 degrees of latitude within a 3-month period between late August and early November 2003. Next-generation sequencing targeting the Bacteria, Archaea, and Eukarya yielded ~ 10.8 million high-quality sequences. Beta-analysis revealed geographic patterns of microbial communities, primarily the Bacteria and Archaea domains. None of the domains exhibited a unimodal pattern of alpha-diversity with respect to latitude. Bacteria communities increased in richness from Arctic to Antarctic waters, whereas Archaea and Eukarya communities showed no latitudinal or polar trends. Based on our analyses, environmental factors related to latitude thought to influence various macrofauna may not define microplankton diversity patterns of richness in the global ocean.