Scientists studying microbes in 'desert' waters of the South Pacific Ocean intrigued by how the organisms adapt
The South Pacific Gyre, which covers 10% of the ocean’s surface, is one of Earth's remotest and least-studied places. The region carries some of the cleanest waters on Earth
An expedition, stretching from South America's Chile to New Zealand, has documented the tiniest residents of one of the world's most inhospitable regions: the South Pacific Gyre. The findings that are a part of a new study also suggests that one microbial inhabitant could have adapted to survive on the surface waters.
Located in the center of the South Pacific Ocean, the South Pacific Gyre is one of Earth's remotest and least-studied places. It carries some of the cleanest waters on Earth. It covers 37 million km2, which equals 10% of the ocean’s surface. The US, on the other hand, occupies less than 10 million km2. Despite its enormous size, the stretch is a biological desert. The waters are nutrient-poor or ultraoligotrophic. The region also experiences dangerously high UV levels. However, the deepest part of the ocean appears to be shielded. It is home to phytoplankton, the primary producers in the aquatic food chain.
There is some mystery surrounding the inhabitants. "The primary reason for the lack of microbial data on the South Pacific Gyre is due to its vast size and remoteness. Few scientific expeditions have traversed it due to high expedition costs," researchers from Max Planck Institute for Marine Microbiology wrote in their study.
To fill the knowledge gap, the team probed the waters along a 7,000 kilometre stretch from Chile to New Zealand. They hoped to uncover more on the microbes, including its diversity and abundance. Helping them was a sophisticated instrument designed to scan and sequence microbial DNA in the makeshift lab onboard. "We developed a novel on-board analysis pipeline, which delivers information on bacterial identity only 35 hours after sampling," Greta Reintjes, one of the authors of the study, said in a statement.
During the cruise, they collected 147 samples from multiple depths --from the surface to the seafloor-- at 11 stations and profiled them. The surface waters hosted fewer microbes than other parts of the oceans. “It was probably the lowest cell numbers ever measured in oceanic surface waters," Bernhard Fuchs, one of the study's authors, said. Further, the identified microbial inhabitants were familiar to the scientists, as the same resided in other nutrient-poor ocean regions. Some of them include, Prochlorococcus, SAR11, SAR86 and SAR116, Fuchs added. But one organism in the surface waters took the researchers by surprise: AEGEAN-169, which, until then, occupied only deeper reaches of the ocean.
Like phytoplankton, various bacteria showed a propensity for the deepest part of the oceans, according to Fuchs and his colleagues.“The community composition changed strongly with depth, which was directly linked to the availability of light”, Reintjes explained. For instance, Prochlorococcus was sparse on the surface but more prevalent at 100 to 150 meters below.
The exception was AEGEAN-169, which appeared to have developed an affinity for the surface. “This indicates an interesting potential adaptation to ultraoligotrophic waters and high solar irradiance," Reintjes added. However, it is also likely that multiple species exist within this group. The team will carry out further studies to examine their importance in the nutrient-deficient waters of the South Pacific Gyre, she added.