Mixotropic plankton may have big effect on ocean’s carbon storage

Researchers at MIT and Bristol University in the United Kingdom have found that these microscopic, mixotrophic organisms may have a large impact on the ocean’s food web and the global carbon cycle.

The scientists developed a mixotrophic model of the global ocean food web, at the scale of marine plankton, in which they gave each plankton class the ability to both photosynthesize and consume prey. They found that, compared with traditional models that do not take mixotrophs into account, their model produced larger, heavier plankton throughout the ocean. As these more substantial microbes die, the researchers found they increase the flux of sinking organic carbon particles by as much as 35 percent.

The results, says Mick Follows, associate professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, suggest that mixotrophic organisms may make the ocean more efficient in storing carbon, which in turn enhances the efficiency with which the oceans sequester carbon dioxide.

In the oceans, plankton can range in size from less than 1 micron, to about 1 millimeter in diameter. Typical ocean models that incorporate plankton often group them in 10 general size classes, each of which fall into a “two-guild” structure, as either photosynthesizers, or consumers of prey.

“If (mixotrophs) weren’t in the oceans, we’re suggesting atmospheric carbon dioxide might be higher, because there would less of the large, carbon rich particles formed which efficiently transfer carbon to depth,” Mick Follows says. Image: James Fraser/Biodiversity Heritage Library