{"id":211321,"date":"2025-09-08T23:15:15","date_gmt":"2025-09-08T23:15:15","guid":{"rendered":"https:\/\/www.europesays.com\/us\/211321\/"},"modified":"2025-09-08T23:15:15","modified_gmt":"2025-09-08T23:15:15","slug":"warming-seas-may-halve-key-phytoplankton-species-population-in-tropical-oceans","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/us\/211321\/","title":{"rendered":"Warming seas may halve key phytoplankton species\u2019 population in tropical oceans"},"content":{"rendered":"

SEATTLE (AP) \u2014 For decades, scientists believed Prochlorococcus, the smallest and most abundant phytoplankton on Earth, would thrive in a warmer world. But new research suggests the microscopic bacterium, which forms the foundation of the marine food web<\/a> and helps regulate the planet\u2019s climate, will decline sharply as seas heat up.<\/p>\n

A study published Monday<\/a> in the journal Nature Microbiology found Prochlorococcus populations could shrink by as much as half in tropical oceans over the next 75 years if surface waters exceed about 82 degrees Fahrenheit (27.8 Celsius). Many tropical and subtropical sea surface temperatures are already trending above average<\/a> and are projected to regularly surpass 86 degrees Fahrenheit (30 Celsius) over that same period. <\/p>\n

\u201cThese are keystone species \u2014 very important ones,\u201d said Fran\u00e7ois Ribalet, a research associate professor at the University of Washington\u2019s School of Oceanography and the study\u2019s lead author. \u201cAnd when a keystone species decreases in abundance, it always has consequences on ecology and biodiversity. The food web is going to change.\u201d<\/p>\n

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\"Francois<\/p>\n

Francois Ribalet, a research associate professor at the University of Washington\u2019s School of Oceanography, pulls a vial of Prochlorococcus on Friday, Sept. 5, 2025, in Seattle. (AP Photo\/Annika Hammerschlag)<\/p>\n

Francois Ribalet, a research associate professor at the University of Washington\u2019s School of Oceanography, pulls a vial of Prochlorococcus on Friday, Sept. 5, 2025, in Seattle. (AP Photo\/Annika Hammerschlag)<\/p>\n

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These tiny organisms hold a vital role in ocean life<\/p>\n

Prochlorococcus inhabit up to 75% of Earth\u2019s sunlit surface waters and produce about one-fifth of the planet\u2019s oxygen through photosynthesis. More crucially, Ribalet said, they convert sunlight and carbon dioxide into food at the base of the marine ecosystem.<\/p>\n

\u201cIn the tropical ocean, nearly half of the food is produced by Prochlorococcus,\u201d he said. \u201cHundreds of species rely on these guys.\u201d<\/p>\n

Though other forms of phytoplankton may move in and help compensate for the loss of oxygen and food, Ribalet cautioned they are not perfect substitutes. \u201cEvolution has made this very specific interaction,\u201d he said. \u201cObviously, this is going to have an impact on this very unique system that has been established.\u201d<\/p>\n

The findings challenge decades of assumptions that Prochlorococcus would thrive as waters warmed. Those predictions, however, were based on limited data from lab cultures. For this study, Ribalet and his team tested water samples while traversing the Pacific over the course of a decade. <\/p>\n

Over 100 research cruises \u2014 the equivalent of six trips around the globe \u2014 they counted some 800 billion individual cells taken from samples at every kilometer. In his lab at the University of Washington, Ribalet demonstrated the SeaFlow, a box filled with tubes, wires and a piercing blue laser. The custom-built device continuously pulls in seawater, which allowed the team to count the microbes in real time. \u201cWe have counted more Prochlorococcus than there are stars in the Milky Way,\u201d Ribalet said.<\/p>\n

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\"The<\/p>\n

The SeaFlow, a custom-built flow cytometer developed by University of Washington researchers, which uses lasers to detect Prochlorococcus, sits in a lab on Friday, Sept. 5, 2025, in Seattle. (AP Photo\/Annika Hammerschlag)<\/p>\n

The SeaFlow, a custom-built flow cytometer developed by University of Washington researchers, which uses lasers to detect Prochlorococcus, sits in a lab on Friday, Sept. 5, 2025, in Seattle. (AP Photo\/Annika Hammerschlag)<\/p>\n

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Experts warn of \u2018big consequences\u2019<\/p>\n

Paul Berube, a research scientist at Massachusetts Institute of Technology who studies Prochlorococcus but was not involved in the work, said the breadth of data is \u201cgroundbreaking.\u201d And he said the results fit with what is known about the microbe\u2019s streamlined genome, which makes it less adaptable to rapid environmental changes. <\/p>\n

\u201cThey\u2019re at the very base of the food web, and they feed everything else \u2014 the fish eat the things that eat the phytoplankton and we eat the fish,\u201d he said. \u201cWhen changes are being made to the planet that influence these particular organisms that are essentially feeding us, that\u2019s going to have big consequences.\u201d<\/p>\n

To test whether Prochlorococcus might evolve to withstand hotter conditions, Ribalet\u2019s team modeled a hypothetical heat-tolerant strain but found that even those would \u201cnot be enough to fully resist the warmest temperature if greenhouse emissions keep rising,\u201d Ribalet said.<\/p>\n

He stressed that the study\u2019s projections are conservative and don\u2019t account for the impacts of plastic pollution or other ecological stressors. \u201cWe actually tried to put forth the best-case scenario,\u201d Ribalet said. \u201cIn reality, things may be worse.\u201d<\/p>\n

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\"Francois<\/p>\n

Francois Ribalet, a research associate professor at the University of Washington\u2019s School of Oceanography, works atop a SeaFlow, an instrument used to detect Prochlorococcus, in his Seattle lab Friday, Sept. 5, 2025. (AP Photo\/Annika Hammerschlag)<\/p>\n

Francois Ribalet, a research associate professor at the University of Washington\u2019s School of Oceanography, works atop a SeaFlow, an instrument used to detect Prochlorococcus, in his Seattle lab Friday, Sept. 5, 2025. (AP Photo\/Annika Hammerschlag)<\/p>\n

Read More<\/p>\n

Steven Biller, an associate professor at Wellesley College, said the projected declines are \u201cscary but plausible.\u201d He noted Prochlorococcus form part of the \u201cinvisible forests\u201d of the ocean \u2014 tiny organisms most people never think about, but are essential to human survival.<\/p>\n

\u201cHalf of all photosynthesis is happening in the oceans and Prochlorococcus is a really important part of that,\u201d Biller said. \u201cThe magnitude of the potential impact is kind of striking.\u201d<\/p>\n

Biller, Berube and Ribalet said that while other microbes may compensate somewhat, the broader risks to biodiversity and fisheries are real.<\/p>\n

\u201cWe know what drives global warming. There is no debate among the scientific community,\u201d Ribalet said. \u201cWe need to curb greenhouse gas emissions.\u201d<\/p>\n

He hopes the findings bring more attention to tropical oceans, which could serve as natural laboratories for warming adaptations and as early warning signals for ecological collapse.<\/p>\n

\u201cFor the first time, I want to be wrong. I would love to be wrong,\u201d he said. \u201cBut these are data-driven results.\u201d<\/p>\n

___<\/p>\n

Follow Annika Hammerschlag on Instagram @ahammergram.<\/a><\/p>\n

___<\/p>\n

The Associated Press receives support from the Walton Family Foundation for coverage of water and environmental policy. The AP is solely responsible for all content. For all of AP\u2019s environmental coverage, visit https:\/\/apnews.com\/hub\/climate-and-environment<\/a><\/p>\n