Scientists have completed an “unparalleled investigation” of one of the most remote, lifeless, and least studied regions on planet Earth, right at the heart of the South Pacific Ocean. While home to a graveyard of satellites, chemical sludge, and heaps of floating plastic trash, this ocean desert is notoriously scant when it comes to any form of life due to its dangerously high levels of UV light from the Sun and lack of nutrients.
Nevertheless, a detailed inventory of the South Pacific Gyre by the Max Planck Institute for Marine Microbiology has revealed that this strange patch of crystal clear water is home to a host of unexpected microbial communities.
The South Pacific Gyre covers over 37 million square kilometers (14.2 million square miles) of ocean – that’s a greater area than the US, Canada, and China combined. The lack of bacteria and organic matter here makes the surface waters the clearest in the world. However, the region gathers up pollution and debris due to a strong system of rotating ocean currents.
Reporting in the journal Applied and Environmental Microbiology, scientists sampled the microbial community at 15 points at water depths ranging from 20 to over 5,000 meters (65-16,400 feet) while working from the German research vessel Sonne.
"It was probably the lowest cell numbers ever measured in oceanic surface waters," Bernhard Fuchs, from the Max Planck Institute for Marine Microbiology, said in a statement. "To our surprise, we found about a third [fewer] cells in South Pacific surface waters compared to ocean gyres in the Atlantic.
”We found similar microbial groups in the gyre as in other nutrient-poor ocean regions, such as Prochlorococcus, SAR11, SAR86, and SAR116.”
The area was defined by 20 major bacterial clades. Much to the team's surprise, the most dominant photosynthetic organism, a photosynthetic picoplankton known as Prochlorococcus, was scarcely found in the uppermost waters where the most sunlight is. Instead, it was most frequent at depths of between 100 and 150 meters (328-492 feet).
They also documented high levels of AEGEAN-169 in the well-lit sparkling surface waters. This was especially surprising since this organism was previously only reported in the darkest depths of the sea.
The researchers note that the composition of microbes living here appears to have shifted around in an attempt to adapt to ultra-low levels of nutrients and super-high levels of solar irradiance.
“This indicates an interesting potential adaptation to ultraoligotrophic waters and high solar irradiance. It is definitely something we will investigate further,” researcher Greta Reintjes explained.
“It is likely that there are multiple ecological species within this group and we will carry out further metagenomic studies to examine their importance in the most oligotrophic waters of the South Pacific Gyre.”