Marine fertility: Researchers study how nutrients get to the bottom of the food web

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Almost all marine life—fish, turtles, sharks, whales, and more—depends on marine food webs for survival. However, the foundation of this enormous flow of energy lies on the shoulders of the microscopic but mighty phytoplankton.

Without essential nutrients such as phosphorus, the growth of these tiny floating marine plants is limited, and the effects of such restrictions flow through the ecosystem, impacting the abundance and diversity of marine creatures. A team of Florida State University and New Hampshire University researchers have published a new study looking at how one important source of the nutrient, dissolved organic phosphorus, is distributed across the global ocean surface where it is consumed by phytoplankton.

The work was published today in Natural Geoscience.

All living organisms, including phytoplankton, need phosphorus to synthesize DNA, RNA and other important organic compounds. In addition to functioning as the basis of the marine food web, phytoplankton that grows on the surface of the sea also plays an important role in regulating the concentration of carbon dioxide in the atmosphere, thus affecting the climate.

Associate Professor of Earth, Ocean and Atmospheric Science Angela Knapp and doctoral candidate Zhou Liang found that the availability of phosphate and iron is the biggest factor influencing the distribution of dissolved organic phosphorus throughout the oceans. Although the researchers suspected the influence of phosphate in the overall process, knowing that iron availability also played an important role was not unexpected.

“This work provides new insights into what controls ocean fertility,” said Knapp, a professor in FSU’s Department of Earth, Oceanic and Atmospheric Sciences.

The researchers 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 across ocean basins. Liang noted the new measurements and combed through existing research until the patterns of influence of phosphate and iron availability became clear.

“Dissolved organic phosphorus can be an alternative source of nutrients to support the growth of phytoplankton at sea level when phosphate concentrations are low,” said Liang, lead author. “Iron is also scarce at sea level, and while investigating the relationship between phosphate and dissolved organic phosphorus, I noticed that certain enzymes released by phytoplankton require iron to function properly. Understanding what controls the consumption of dissolved organic phosphorus by phytoplankton can help us better understand the impact of nutrients on marine nitrogen fixation rates, photosynthetic rates, and phytoplankton uptake of carbon dioxide.”

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

“Scientific modelers can use this hypothesis to better constrain nutrient budgets and photosynthesis rates, and experimentalists can design new culture work to test them,” Liang said. “Marine scientists understand sample gaps and where more data is needed; these links are interdisciplinary and will encourage more collaboration among scientists such as trace metals researchers, nutrition researchers, biological oceanographers and modelers.”

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

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Plankton is more resistant to nutrient stress than previously thought

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Further information:
Zhou Liang et al, The concentration of dissolved organic phosphorus at sea level is controlled by phosphate and iron stress, Natural Geoscience (2022). DOI: 10.1038/s41561-022-00988-1

Provided by Florida State University

Quote: Marine fertility: Researchers study how nutrient sources get to the bottom of the food web (2022, 21 July) retrieved 21 July 2022 from https://phys.org/news/2022-07-fertility-sea-nutrient-sources-base.html

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