Sargasso Sea Plankton and Other Marine Microbes Take Turns Sharing Nutrients
A new study co-authored by UMD biologist Joshua Weitz found that microbes divvy nutrients over time, reducing competition for limited resources.
In the 1960s, ecologist G. Evelyn Hutchinson raised a puzzling question: Why do so many phytoplankton species exist? The ocean teems with these photosynthesizing bacteria, but mathematically, they shouldn’t all survive while competing for limited nutrients.
One hypothesis for solving “the paradox of the plankton,” as it’s known, comes from land. Many terrestrial animals exhibit distinct activity cycles, including foraging behaviors that minimize conflict for limited food supplies over a 24-hour period. That led researchers to wonder if plankton diversity might stem from absorbing scarce nutrients at different times of day.
New evidence supports that theory. University of Maryland biologist Joshua Weitz and collaborators at other institutions found cellular-level evidence of temporal niche partitioning among plankton in a long-term study site in the North Atlantic Ocean.
Their study, published in the journal Proceedings of the National Academy of Sciences (PNAS) on March 14, 2025, showed that phytoplankton and other microbes in the Atlantic Ocean’s Sargasso Sea take turns utilizing phosphorus, a critical nutrient for their growth but one that remains scarce in this region. This new finding echoes a previous study co-authored by Weitz that showed that plankton in the north Pacific Ocean used temporal niche partitioning to reduce competition for nitrogen, another limiting nutrient.
“We went to a completely different ocean, did a comparable study and found the same signature of temporal niche partitioning for phosphorus as we did for nitrogen,” said the study’s first author, Daniel Muratore, a postdoctoral fellow at the Santa Fe Institute and a former student of Weitz’s. “This suggests that reducing competition by taking turns might be a general feature of maintaining biodiversity in the ocean microbiome.”
At its core, this research reveals the complex interplay between the billions of microbes that share limited resources in a single liter of ocean water. This includes phytoplankton, heterotrophic bacteria and cyanobacteria—some of Earth’s smallest forms of self-sustaining life.
“This project explored ways in which cellular activity varied over the course of the day. We found that organisms are dividing their utilization of nutrients in time rather than in space,” said Weitz, the study’s co-principal investigator and a professor in UMD’s Department of Biology who holds the Clark Leadership Chair in Data Analytics. “We now have evidence of temporal niche partitioning occurring in this complex world of the very small.”
The data for the PNAS study came from a five-day research cruise to the Sargasso Sea in 2019. The researchers collected, filtered out and froze sea-dwelling cells every four hours, then took those cells back to the lab to extract and sequence the cells’ RNA. Doing so painted a more vivid picture of the organisms’ activity over the course of a day.
After analyzing 97,829 genes, the co-authors found gene expression patterns suggesting that different microbial species absorb phosphorus at different times of day. Bacteria that primarily rely on dissolved organic matter consumed phosphorus at sunrise, while photosynthesizing plankton with nuclei waited until daytime and cyanobacteria got their share at dusk.
According to Weitz, the findings may indicate that these microbes coevolved together, influencing each other to develop compatible strategies for nutrient uptake.
“We think this is an emergent feature within complex microbial communities,” Weitz explained. “We think that temporal niche partitioning facilitates coexistence of more microbial types than in cases where each microbe competes at the same time of day for a scarce nutrient.”
Phosphorus is a key component of RNA, DNA, cell membranes and energy storage. Understanding how plankton consume phosphorus can also help predict how ocean life will respond to human-driven climate change.
“As the climate continues changing from additional greenhouse gases in the atmosphere, so too will ocean chemistry,” Muratore said. “By discovering how ecosystems handle nutrient uptake, we can also take steps to predict if and when they are vulnerable to crashing.”
Going forward, Weitz believes that their methods could help other researchers studying temporal niche partitioning in species worldwide.
“We have developed computational methods to parse a large amount of cellular activity data in ways that can help others identify when microbes limit competition with one another,” Weitz said. “In that sense, it’s really exciting to take gene expression signals and get a glimpse of principles that may help sustain diverse microbial life in the global oceans.”
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This article was adapted from text provided by the Santa Fe Institute.
The paper, “Diel partitioning in microbial phosphorus acquisition in the Sargasso Sea,” was published in PNAS on March 14, 2025.
This research was supported by the U.S. National Science Foundation (Grant Nos. OCE-1829641 and OCE-1829636), the Simons Foundation (Grant No. 721231) and the Blaise Pascal Institute Chair of Excellence award at the Institut de Biologie of the École Normale Supérieure. This article does not necessarily reflect the views of these organizations.
