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Researchers study how nutrient sources make it to the base of the food web


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Virtually all marine life – fish, turtles, sharks, whales and more – depends on the marine food web for survival. However, the basis of this immense energy flow rests on the shoulders of the microscopic but mighty phytoplankton.

Without essential nutrients such as phosphorus, the growth of these small floating ocean plants is limited, and the effects of such restriction flow through the ecosystem, affecting the abundance and diversity of marine animals. A research team from Florida State University and the University of New Hampshire has published a new study looking at how an important nutrient source, dissolved organic phosphorus, is distributed from the ocean to the surface, where it is consumed by phytoplankton.

The work was published today in Natural Geosciences.

All living organisms, including phytoplankton, need phosphorus to synthesize DNA, RNA, and other essential organic compounds. In addition to serving as the foundation of the marine food web, phytoplankton that grow on the ocean’s surface also play an essential role in regulating atmospheric carbon dioxide concentrations, influencing the climate.

Associate professor of Earth, Ocean and Atmospheric Science Angela Knapp and PhD student Zhou Liang found that the availability of phosphate and iron are the biggest factors influencing the distribution of dissolved organic phosphorus through the ocean. Although the researchers suspected the influence of phosphate in the overall process, it was unexpected to find that the availability of iron also played an important role.

“This work provides new insights into what regulates ocean fertility,” said Knapp, an associate professor in FSU’s Division of Earth, Ocean and Atmospheric Science.

Researchers have compiled a new global ocean dataset of dissolved organic phosphorus concentrations by analyzing thousands of samples from different ocean regions, including samples collected during expeditions traversing ocean basins. Liang recorded new measurements and combed through existing research until the pattern of the phosphate and iron availability influence became clear.

“Dissolved organic phosphorus may be an alternative food source to support the growth of surface ocean phytoplankton when phosphate concentrations are low,” said Liang, the lead author. “Iron is also scarce at the ocean’s surface, and while investigating the relationship between phosphate and dissolved organic phosphorus, I noticed that certain enzymes released by phytoplankton require iron to function properly. If we understand what the consumption of dissolved organic phosphorus by phytoplankton, we can better understand the nutrient’s impact on marine nitrogen fixation, photosynthesis rate and carbon dioxide sequestration by phytoplankton.”

The discovery of the influence of iron on concentrations is relevant to a wide range of biogeochemists, and this work also proposes a set of expectations for dissolved organic phosphorus that can be tested experimentally.

“Scientific modelers can use these hypotheses to better limit nutrient budgets and photosynthesis rates, and experimenters can design new culture work to test them,” Liang said. “Oceangoing scientists understand gaps in the sample and where more data is needed; these links are interdisciplinary in nature and will encourage more collaborations among scientists such as trace metal researchers, nutrient researchers, biological oceanographers and modellers.”

Robert Letscher, assistant professor of Earth Sciences in the UNH Ocean Process Analysis Laboratory and the UNH College of Engineering and Physical Sciences at the University of New Hampshire, contributed to this research.

Plankton is more resistant to nutritional stress than previously thought

More information:
Zhou Liang et al, Dissolved ocean organic phosphorus concentrations at the surface controlled by both phosphate and iron stress, Natural Geosciences (2022). DOI: 10.1038/s41561-022-00988-1

Provided by Florida State University

Quote: Fertility of the Sea: Researchers Study How Nutrients Reach the Base of the Food Web (July 2022, July 21) Retrieved July 21, 2022 from https://phys.org/news/2022-07-fertility-sea-nutrient -sources- base.html

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