Researchers emphasize the need for basic information on microbial food webs


The hydrothermal discharge fluids from the dispersal center of Gorda Ridge in the Northeast Pacific create a center of biological activity in the deep sea. There, in the dark ocean, a unique food web does not live from photosynthesis, but from the chemical energy of the escaping liquids. Among the creatures that spend a day in the field at Gorda Ridge Chimneys is a diverse selection of microbial eukaryotes or protists that graze on chemosynthetic bacteria and archaea.

This Protistan willow, which is a key mechanism for carbon transport and recycling in microbial food webs, exerts more predatory pressure on hydrothermal springs than in the surrounding deep-sea environment, according to a new paper.

“Our results provide an initial estimate of Protistan grazing pressures in hydrothermal food webs and underscore the important role that various deep-sea Protistan communities play in the deep-sea carbon cycle,” states the paper. Protistan grazing affects microbial communities and the carbon cycle ad Deep sea hydrothermal vents published in the Proceedings of the National Academy of Sciences (PNAS).

Protists serve as the link between primary producers and higher trophic levels, and their grazing is a key mechanism for carbon transport and recycling in microbial food webs, the paper says.

Research found that protists consume 28-62% of daily bacterial and archaeal biomass stocks by draining hydrothermal vent fluids from Gorda Ridge, which is about 200 kilometers off the coast of southern Oregon. In addition, the researchers estimate that Protistan grazing could be responsible for the consumption or transfer of up to 22% or carbon that is fixed in the runoff fluids by the chemosynthetic population. Although the fate of all this carbon is unclear, “grazing Protistan releases some of the organic carbon into the microbial cycle through excretion, egestion, and sloppy feeding,” and some of the carbon is ingested by larger organisms that consume Protistan cells the paper says.

After collecting vent fluid samples from the Sea Cliff and Apollo hydrothermal vent fields in Gorda Ridge, the researchers conducted pasture experiments that posed some technical challenges to overcome. “For example, it is very difficult to prepare a quality meal for these protists,” said lead author Sarah Hu, a postdoctoral fellow in the Department of Marine Chemistry and Geochemistry at the Woods Hole Oceanographic Institution (WHOI).

“To be able to do this research at a deep-sea vent was really exciting because the food web there is so fascinating and it’s powered by what happens to that vent that leaks,” said Hu, who was aboard the E / V Nautilus during the cruise from May to June 2019. “There is this whole microbial system and community operating there beneath the euphotic zone out of the reach of sunlight. I was excited to expand our knowledge of the microbial communities at these vents.”

Hu and co-author Julie Huber said quantitative measurements are important in understanding how food webs function on pristine and undisturbed sources.

“The ocean offers us a number of ecosystem services that many people are familiar with, such as seafood and carbon sinks. However, when we think of microbial ecosystem services, especially in the deep sea, we just don’t have that much data. “About how these food webs work,” said Huber, associate scientist in the WHOI’s Department of Marine Chemistry and Geochemistry.

Getting baseline measurements “is becoming increasingly important as these habitats are being studied for deep-sea mining or carbon sequestration. How might that affect how much carbon is produced, exported, or recycled?” She said.

“We have to understand these habitats and the ecosystems that support them,” said Huber. “This research connects some new points that we couldn’t connect before.”

The research was supported by NASA, the National Oceanic and Atmospheric Administration, the Ocean Exploration Trust, the National Science Foundation, and WHOI.

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