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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 finite food supplies over a 24-hour period. That led researchers to wonder if plankton diversity might stem from absorbing 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 this “temporal niche partitioning” among plankton in a long-term study site in the North Atlantic Ocean.
Their study, published Friday in the journal Proceedings of the National Academy of Sciences, showed that phytoplankton and other microbes in the Atlantic Ocean’s Sargasso Sea take turns using 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.
“This suggests that reducing competition by taking turns might be a general feature of maintaining biodiversity in the ocean microbiome,” said the study’s first author, Daniel Muratore, a postdoctoral fellow at the Santa Fe Institute and a former student of Weitz’s.
The data for the PNAS study came from a five-day research cruise in 2019. The researchers collected, filtered out and froze sea-dwelling cells every four hours, later sequencing 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.
This article was adapted from text provided by the Santa Fe Institute.
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