Prochlorococcus marinus is present in all tropical and subtropical oceans, where it is often
found throughout the euphotic zone, contributing significantly to phytoplankton biomass and
primary production and growing at rates comparable to those of other picoplankters. Clearly,
Prochlorococcus and eucaryotic picoplankton share significant niche dimensions in the
open ocean. Here we report the discovery of populations of Prochlorococcus in layers below
the oxyclines of the oxygen minimum zones of the Arabian Sea and the Eastern Tropical …