A six-year analysis of marine microorganisms in California’s coastal waters has overturned long-held assumptions about how the ocean’s smallest organisms interact.

Researchers at the Scripps Institution of Oceanography at the University of California, San Diego have discovered that rather than eating or competing with each other, marine microorganisms interact in ways that benefit each other. The researchers also found that periods of warmer ocean temperatures, which are typically stressful for these microbes due to lack of nutrients, actually triggered more of these positive interactions.

The study was published in the journal Jan. 21. ISME Journal: Interdisciplinary Journal of Microbial Ecology Supported by the Simons Foundation, the National Science Foundation, and NOAA.

Marine microorganisms such as bacteria and phytoplankton form the basis of ocean food webs, providing nutrients for organisms ranging from zooplankton to whales and supporting fisheries that feed billions of people. These organisms also help regulate Earth’s climate by cycling carbon, oxygen, and nitrogen through the oceans and atmosphere. But while ecologists have spent decades documenting how wolves, sea otters, and other large animals interact in ecosystems, the relationships between the ocean’s most abundant organisms have received less attention, creating a major gap in our understanding of how marine ecosystems function.

The research team set out to answer three questions: How often and how strongly do marine microorganisms interact? Are there keystone microorganisms that have a disproportionate impact on the community? sea ​​otter?And does ocean temperature affect these interactions??

To find the answer, researchers relied on a unique dataset created by analyzing seawater samples collected twice weekly from San Diego’s Scripps Pier since 2018. Scripps Ecological Observatory and Southern California Coastal Ocean Observation System (Skoos). The power of this dataset comes from its long time series and the fact that it provides a way to observe marine microbial interactions in the ocean, whereas most previous studies on this topic have been conducted in the laboratory.

“Scripps Pier has a long and remarkable observational history. The most famous is temperature. “This time series adds to that legacy by giving us a long-term view of the entire microbial community in these samples,” said Jeff Bowman, a Scripps microbiologist who began the data collection project with his students in 2018. Being able to obtain data from the open ocean without using a ship is a big deal. ”

Using DNA sequencing, the team identified the microorganisms present in samples collected from 2018 to 2023, ultimately tracking the 162 most abundant species. The researchers then applied computational techniques to detect patterns in the data, revealing when changes in the abundance of one organism cause changes in the abundance of another, as opposed to when organisms are simply responding to the same environmental factors.

The analysis revealed three surprising findings. First, positive interactions, where the growth of one microbe promotes the growth of another, were much more common than negative interactions such as competition or predation. Approximately 78% of microorganisms had a net positive impact on their neighboring microorganisms. The study did not reveal the mechanism behind these positive interactions, but Scripps postdoctoral fellow and lead author of the study, Ewa Merz, said a potential example could be one organism releasing waste products that another species uses as nutrients.

Second, the team discovered that there are indeed keystone microbes that interact more with other microbes within a community and have a greater impact on the structure of the community. Third, temperature has dramatically changed the way organisms interact. Across the 13°C (23°F) temperature range observed during the study, warmer conditions reduced microbial community interactions by 33% and shifted 11% to more active interactions. Interestingly, the identity of keystone microbial species changed with temperature.

“Marine ecologists have focused on competitive and predatory interactions and ignored active interactions.” andrew bartona Scripps marine ecologist and lead author of the study. “Our results show that these positive interactions are common and underappreciated.”

The findings suggest that ocean warming may not only change which microorganisms live, but also fundamentally alter the interactions and functions of marine microbial communities. Current marine ecosystem models typically emphasize negative interactions such as competition and predation, ignore facilitation, and do not explicitly account for how interactions vary with environmental conditions. This means that predictions of how marine ecosystems will respond to warming may be missing important dynamics. These invisible changes can have far-reaching effects, as marine microbes regulate carbon sequestration and support the fisheries on which humans depend.

The authors recommend that future microbial community models incorporate positive interactions and attempt to account for how relationships between species change with environmental conditions. They also point out that their approach, which combines long-term, high-frequency sampling and computational methods, could be applied to microbial communities in other settings, such as soil or the human gut, to reveal similar hidden dynamics. As ocean temperatures continue to rise, understanding how the microscopic infrastructure of marine life responds is essential to predicting changes in the ecosystems and services that depend on it.

In addition to Merz, Bowman and Barton, co-authors on the study include Riley Hale, Erik Saberski, Kasia Kenitz and Melissa Carter of Scripps Oceanography and SCCOOS.

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