Climate change may produce “fast-food” phytoplankton

As sea surface temperatures rise over the next century, phytoplankton in polar regions will adapt to be less rich in proteins, heavier in carbohydrates, and lower in nutrients overall. “We’re moving in the poles toward a sort of fast-food ocean,” says MIT postdoc Shlomit Sharoni.
Image Credits: Jose-Luis Olivares, MIT; iStock
(CC BY-NC-ND 3.0)

Scientific Frontline: Extended "At a Glance" Summary: Fast-Food Phytoplankton

The Core Concept: As ocean temperatures rise and sea ice diminishes due to climate change, marine phytoplankton are adapting by shifting from a protein-rich nutritional profile to a carbohydrate- and lipid-heavy composition, effectively becoming a less nutritious "fast food" for the marine ecosystem.

Key Distinction/Mechanism: While previous ecological studies primarily focused on how climate change affects the population sizes and distribution of phytoplankton, this research explicitly models their internal macromolecular readjustment. As sea ice melts and sunlight becomes more abundant in polar regions, phytoplankton require fewer light-harvesting proteins to perform photosynthesis, resulting in a proportional increase in carbohydrates and lipids.

Origin/History: The findings were published in Nature Climate Change on March 31, 2026, by a research team led by MIT postdoctoral researcher Shlomit Sharoni. The conclusions were derived from synthesizing historical field sample data with advanced climate projections extending to the year 2100.

Major Frameworks/Components:

• Macromolecular Composition Modeling: A quantitative framework simulating how marine microalgae balance essential macromolecules (proteins, lipids, carbohydrates, and nucleic acids) under varying environmental conditions.
• Ocean Circulation Dynamics: The integration of lab-based biological data with established ocean circulation models to predict the impact of a 3-degree Celsius sea surface temperature rise, reduced sea ice, and restricted nutrient upwelling.
• Latitudinal Divergence: The model predicts distinct regional adaptations; polar phytoplankton will experience up to a 30 percent decline in protein content, whereas subtropical populations—facing reduced nutrient upwelling—may shift to deeper waters and adopt a slightly more protein-rich composition to maximize limited sunlight.

Mystery in the Gulf

The Hillsborough River at Rotary River Park. One of several sites where project scientists will collect samples to measure the iron and nitrogen content of the Hillsborough River,which carries nutrients into Tampa Bay and into the Gulf of Mexico.
Credit: Tim Conway, USF.

West of St. Petersburg in the Gulf of Mexico is an area called the West Florida Shelf. It’s a marine desert, cut off from many of the elements that are essential for life.

But in this nutrient-deficient region, some forms of phytoplankton — microscopic plants that float through the water — are thriving and supporting other forms of life. But how?

Florida State University Associate Professor Angie Knapp and a team of researchers from around the country have received a $2.3 million grant from the National Science Foundation to investigate this oceanographic mystery. Knapp, part of the Department of Earth, Ocean and Atmospheric Science in the College of Arts and Sciences, will lead the project to examine how iron and nitrogen released from submarine groundwater discharge potentially serves as a fertilizer for phytoplankton in this area and beyond.

“Plant growth in the ocean plays an important role in regulating atmospheric carbon dioxide concentrations, which plays an important role in regulating climate,” Knapp said. “However, plant growth in the ocean is often limited by the availability of nitrogen; thus, we’re focusing on the processes that add and remove nitrogen to and from the ocean.”

Algae bio hacks itself in adapting to climate change

Phytoplankton - the foundation of the oceanic food chain.
Photo Credit: NOAA

Clear evidence that marine phytoplankton are much more resilient to future climate change than previously thought is the focus of a study published in Science Advances by an international team of scientists, including University of Hawaiʻi at Mānoa oceanography professor David Karl.

“Knowing how marine algae will respond to global warming and to associated decline of nutrients in upper ocean waters is crucial for understanding the long-term habitability of our planet,” said Karl.

Combining data from the long-term Hawaiʻi Ocean Time-series program at UH Mānoa with new climate model simulations conducted on one of South Korea’s fastest supercomputers, the scientists revealed that a mechanism, known as nutrient uptake plasticity, allows marine algae to adapt and cope with nutrient-poor ocean conditions that are expected to occur over the next decades in response to global warming of the upper ocean.

What Is: Phytoplankton

Image Credit: Scientific Frontline

Scientific Frontline: Extended "At a Glance" Summary: Phytoplankton

The Core Concept: Phytoplankton are microscopic, single-celled autotrophs that drift within the sunlit upper layers of the global ocean. They form the foundational base of the marine food web and act as the primary drivers of planetary-scale biogeochemical cycles.

Key Distinction/Mechanism: Unlike mature terrestrial ecosystems, such as the Amazon Rainforest, which consume nearly all the oxygen they generate through aerobic and heterotrophic respiration, phytoplankton enable a permanent net accumulation of atmospheric oxygen. When they die, a fraction of their organic carbon sinks and is buried in anoxic ocean sediments, decoupling it from the biological carbon cycle and leaving the synthesized oxygen in the atmosphere.

Origin/History: Ancestral cyanobacteria evolved the capacity for oxygen-producing photosynthesis between 2.9 and 2.5 billion years ago. This biological innovation eventually triggered the Great Oxidation Event (2.4 to 2.1 billion years ago), fundamentally altering Earth's atmosphere and allowing for the eventual evolution of complex aerobic life.

Lake Ecosystems: Nitrogen has been underestimated

Algae growth in shallow lakes around the world is affected not only by phosphorus but also by nitrogen
Photo Credit: Liz Harrell

An ecological imbalance in a lake can usually be attributed to increased nutrient inputs. The result: increased phytoplankton growth, oxygen deficiency, toxic cyanobacterial blooms and fish kills. Until now, controls in lake management have focused primarily on phosphorus inputs to counteract this effect. Now, this dogma is shaken by a study performed by the Helmholtz Centre for Environmental Research (UFZ) in collaboration with the University of Aarhus (Denmark) and the University of Life Sciences (Estonia) and published in Nature Communications. The researchers show that nitrogen is also a critical driver for phytoplankton growth in lakes worldwide. 

The input of phosphorus and nitrogen from agricultural sources and sewage treatment plants can have a strong effect on phytoplankton growth in rivers and lakes. "However, it was previously assumed that phytoplankton growth in lakes is mostly limited and driven by the availability of phosphorus," says lead author Dr. Daniel Graeber from the UFZ. The underlying theory: If only small quantities of phosphorus are available in a lake, phytoplankton growth is correspondingly limited. In contrast, large quantities of phosphorus will massively drive phytoplankton growth. "In this explanatory model, nitrogen plays no role," says Graeber. "This is based on the fact that specific cyanobacteria in the water can bind the nitrogen contained in the air and introduce it into the lake. This would therefore preclude a long-term nitrogen deficiency in lakes." Nor could an excess supply of nitrogen promote phytoplankton growth - and therefore could not ultimately give rise to eutrophication. "This model forms the basis for lake management worldwide, where the emphasis has been on controlling phosphorus inputs to counteract lake eutrophication," explains Dr. Thomas A. Davidson, limnologist at Aarhus University and last author of the study. "Reducing phosphorus inputs repeatedly fails to prevent eutrophication. This therefore gave rise to the question of whether the water equation included yet another unknown." In its present study, the research team has now clearly identified nitrogen as such a factor, and is thus indicating new directions for inland water science (limnology) and lake management. 

Volcanic ash may enhance phytoplankton growth in the ocean over 100 km away

Nishinoshima Island, located in the Ogasawara Islands of Japan, is home to an active volcano. Ash from volcanic eruptions there in 2020 could have led to a temporary surge in phytoplankton levels in the seawater 130 km away.
Photo Credit: Ogasawara Village Tourism Bureau

A research group in Japan has suggested that ash released from volcanic eruptions on Nishinoshima Island—part of Japan's Ogasawara Islands—led to a temporary surge in phytoplankton levels in the seawater around Mukojima Island, which is located 130 km northeast of Nishinoshima and is also part of the Ogasawara Islands.

Mukojima lies within the subtropical gyre, a region known for low nutrient and low chlorophyll conditions. The study indicates that ash from the Nishinoshima eruptions was transported by wind and ocean currents to the waters around Mukojima, serving as a nutrient source for phytoplankton growth in that area.

Small eddies play a big role in feeding ocean microbes

This video still of the North Pacific Ocean shows phosphate nutrient concentrations at 500 meters below the ocean surface. The swirls represent small eddies transporting phosphate from the nutrient-rich equator (lighter colors), northward toward the nutrient-depleted subtropics (darker colors).
Credit: Courtesy of the researchers

Subtropical gyres are enormous rotating ocean currents that generate sustained circulations in the Earth’s subtropical regions just to the north and south of the equator. These gyres are slow-moving whirlpools that circulate within massive basins around the world, gathering up nutrients, organisms, and sometimes trash, as the currents rotate from coast to coast.

For years, oceanographers have puzzled over conflicting observations within subtropical gyres. At the surface, these massive currents appear to host healthy populations of phytoplankton — microbes that feed the rest of the ocean food chain and are responsible for sucking up a significant portion of the atmosphere’s carbon dioxide.

But judging from what scientists know about the dynamics of gyres, they estimated the currents themselves wouldn’t be able to maintain enough nutrients to sustain the phytoplankton they were seeing. How, then, were the microbes able to thrive?

Now, MIT researchers have found that phytoplankton may receive deliveries of nutrients from outside the gyres, and that the delivery vehicle is in the form of eddies — much smaller currents that swirl at the edges of a gyre. These eddies pull nutrients in from high-nutrient equatorial regions and push them into the center of a gyre, where the nutrients are then taken up by other currents and pumped to the surface to feed phytoplankton.

Climate change threatens global fisheries

Euchaeta marina (Calanoid Copepod).
Photo Credit: Julian Uribe-Palomino IMOS-CSIRO.

A major study has found that the diet quality of fish across large parts of the world’s oceans could decline by up to 10 per cent as climate change impacts an integral part of marine food chains.

QUT School of Mathematical Sciences researcher Dr Ryan Heneghan led the study published in Nature Climate Change that included researchers from the University of Queensland, University of Tasmania, University of NSW and CSIRO.

They modeled the impact of climate change on zooplankton, an abundant and extremely diverse group of microscopic animals accounting for about 40 per cent of the world’s marine biomass.

Zooplankton is the primary link between phytoplankton—which converts sunlight and nutrients into energy like plants do on land—and fish.  Zooplankton includes groups such as Antarctic krill—a major food source for whales—and even jellyfish.

Phytoplankton uptake of methylmercury is controlled by thiols

In the sea, phytoplankton are the first step when methylmercury is absorbed into the food web. The image was taken under a microscope and shows a spring bloom of phytoplankton in the Bothnian Sea.
 Image Credit: Marlene Johansson

Methylmercury is one of the chemicals that poses the greatest threat to global public health. People ingest methylmercury by eating fish, but how does the mercury end up in the fish? A new study shows that the concentrations of so-called thiols in the water control how available methylmercury is to living organisms.

For methylmercury to enter the food web, it must be absorbed from the water by organisms and the uptake takes place primarily by phytoplankton. This results in a dramatic enrichment, where the levels of methylmercury can increase by a factor of 10,000 to 100,000. However, there is a great deal of variation between different aquatic environments, and it has so far been unclear what controls the process and why the variation is so large.

Effects of Declining Diversity Documented in the World of Microbes

Phytoplankton, seen here inside a flask in the Jackrel Lab, are proving to be a valuable system for studying host-associated microbiomes
Photo Credit: Jackrel Lab / UCSD

Across the tree of life, human activities are accelerating declines in biological species diversity, from deserts to oceans to forests. But what about the microscopic world? Scientists in UC San Diego’s School of Biological Sciences recently investigated how declining biodiversity in tiny ecological systems unseen to the naked eye can carry significant consequences for the health of organisms and ecosystems.

Postdoctoral Scholar Jonathan Dickey and recent master’s graduate Nikki Mercer from Assistant Professor Sara Jackrel’s laboratory studied the implications of declining diversity within microbiomes — communities of microorganisms, such as bacteria, which can form tight associations with their hosts, such as plants and animals. Recent studies in microbial ecology have found that microbiomes can play a key role in regulating host health, leading researchers to believe that as our world changes it is imperative to understand the implications of biodiversity loss within the host microbiome.

Whale poop contains iron that may have helped fertilize past oceans

A blue whale photographed in September 2010.
Photo Credit: NOAA

The blue whale is the largest animal on the planet. It consumes enormous quantities of tiny, shrimp-like animals known as krill to support a body of up to 100 feet (30 meters) long. Blue whales and other baleen whales, which filter seawater through their mouths to feed on small marine life, once teemed in Earth’s oceans. Then over the past century they were hunted almost to extinction for their energy-dense blubber.

As whales were decimated, some thought the krill would proliferate in predator-free waters. But that’s not what happened. Krill populations dropped, too, and neither population has yet recovered.

A recent theory proposes that whales weren’t just predators in the ocean environment. Nutrients that whales excreted may have provided a key fertilizer to these marine ecosystems.

Research led by University of Washington oceanographers supports that theory. It finds that whale excrement contains significant amounts of iron, a vital element that is often scarce in ocean ecosystems, and nontoxic forms of copper, another essential nutrient that in some forms can harm life.

The open-access study, the first to look at the forms of these trace metals in what’s commonly known as whale poop, was published in January in Communications Earth & Environment.

Meltwater influences ecosystems in the Arctic Ocean

Credit: Alfred Wegener Institute for Polar and Marine Research

In the summer months, sea ice from the Arctic drifts through Fram Strait into the Atlantic. Thanks to meltwater, a stable layer forms around the drifting ice atop the more salty seawater, producing significant effects on biological processes and marine organisms. In turn, this has an effect on when carbon from the atmosphere is absorbed and stored, as a team of researchers led by the Alfred Wegener Institute has now determined with the aid of the FRAM ocean observation system. Their findings have just been published in the journal Nature Communications.

Oceans are one of the largest carbon sinks on our planet, due in part to the biological carbon pump: just below the water’s surface, microorganisms like algae and phytoplankton absorb carbon dioxide from the atmosphere through photosynthesis. When these microorganisms sink to the ocean floor, the carbon they contain can remain isolated from the atmosphere for several thousand years. As experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have now discovered, the meltwater from sea-ice floes can delay this process by four months.

From the summer of 2016 to the summer of 2018, the FRAM (Frontiers in Arctic Marine Monitoring) ocean observation system continually gathered data in Fram Strait (between Greenland and Svalbard). Dense clusters of moorings were installed at two sites in the strait in order to monitor as many aspects of the coupled physical-biological processes in the water as possible. Physical, biogeochemical and acoustic sensors throughout the water column and on the ocean floor, as well as devices that gathered water and sediment samples for subsequent laboratory analysis, were used. “For the first time, for two entire years we were able to comprehensively monitor not only the seasonal developments of microalgae and phytoplankton, but also the complete physical, chemical and biological system in which these developments take place,” says Dr. Wilken-Jon von Appen, a climate researcher at the AWI and first author of the study.

Monitoring an ‘anti-greenhouse’ gas: Dimethyl sulfide in Arctic air

Sumito Matoba (left) and Yoshinori Iizuka (right) on the southeastern dome in Greenland, drilling the ice core used in the study
Photo Credit: Sumito Matoba

Data stored in ice cores dating back 55 years brings new insight into atmospheric levels of a molecule that can significantly affect weather and climate.

Dimethyl sulfide (C2H6S) is a small molecule released by phytoplankton in the ocean, which can play a big role in regulating the Earth’s climate. It encourages cloud formation above the sea, and is often called an ‘anti-greenhouse gas’, since clouds block radiation from the sun and lower sea surface temperatures. At least some blocked heat will be retained in the atmosphere, however, so the effects can be complex. Researchers at Hokkaido University have charted evidence for increasing dimethyl sulfide emissions linked to the retreat of sea ice from Greenland as the planet warms. They reported their findings in the journal Communications Earth & Environment.

Walleye struggle with changes to timing of spring thaw

Within a few days of ice-off, when a lakes’ frozen lid has melted away, walleye begin laying eggs and fertilizing them. When lakes thaw earlier than usual, the young walleye that hatch in Midwestern waters may have a more difficult time surviving.
Image Credit: Copilot AI

Walleye are one of the most sought-after species in freshwater sportfishing, a delicacy on Midwestern menus and a critically important part of the culture of many Indigenous communities. They are also struggling to survive in the warming waters of the Midwestern United States and Canada.

According to a new study published in the journal Limnology and Oceanography Letters, part of the problem is that walleye are creatures of habit, and the seasons — especially winter — are changing so fast that this iconic species of freshwater fish can’t keep up.

The timing of walleye spawning — when the fish mate and lay their eggs — has historically been tied to the thawing of frozen lakes each spring, says the study’s lead author, Martha Barta, a research technician at the University of Wisconsin–Madison. Now, due to our changing climate, walleye have been “unable to keep up with increasingly early and more variable ice-off dates,” Barta says.

Within a few days of ice-off, when a lakes’ frozen lid has melted away, walleye begin laying eggs and fertilizing them. In a normal year, that timing sets baby fish up for success once they hatch. But, Barta says, “climate change is interrupting the historical pairing of ice-off and walleye spawning, and that threatens the persistence of walleye populations across the Upper Midwest.”

Marine Biology: In-Depth Description

Photo Credit: Neeraj Pramanik

Marine Biology is the scientific study of organisms in the ocean and other brackish bodies of water. This discipline encompasses a vast spectrum of life forms, ranging from microscopic picoplankton to the blue whale, the largest animal on Earth. It is an integrative field that combines elements of geology, chemistry, physical oceanography, and biology to understand the physiology, behavior, and ecological roles of marine organisms, as well as their complex interactions with the high-salinity environment.

Wildfire Smoke May Have Amplified Arctic Phytoplankton Bloom

Satellite image of plume in eastern Arctic Ocean, Aug. 2014
Source: North Carolina State University

Smoke from a Siberian wildfire may have transported enough nitrogen to parts of the Arctic Ocean to amplify a phytoplankton bloom, according to new research from North Carolina State University and the International Research Laboratory Takuvik (CNRS/Laval University) in Canada. The work sheds light on some potential ecological effects from Northern Hemisphere wildfires, particularly as these fires become larger, longer and more intense.

In the summer of 2014, satellite imagery detected a larger than normal algal bloom in the Laptev Sea, located in the Arctic Ocean approximately 850 kilometers (528 miles) south of the North Pole.

“For a bloom that large to occur, the area would need a substantial influx of new nitrogen supply, as the Arctic Ocean is nitrogen-depleted,” says Douglas Hamilton, assistant professor of marine, earth and atmospheric sciences at NC State and co-first author of a paper describing the work. Hamilton was formerly a research associate at Cornell University, where the research was conducted. “So we needed to figure out where that nitrogen was coming from.”

First, the researchers looked at the “usual suspects” for nitrogen input, such as sea ice melt, river discharge and ocean upwelling, but didn’t find anything that would account for the amount of nitrogen necessary for the bloom to occur.

What is drawing humpback whale super-groups to the African coast?

Super-groups of up to 200 humpback whales appearing off the coast of South Africa are following changing ocean currents and phytoplankton blooms, a new study has found.

Researchers at Griffith University were part of an international team led by the University of Cape Town (UTC) which combined satellite observations and a physical ocean model to intricately map the ocean circulation and productivity using chlorophyll levels in the region over the past 10 years in order to understand environmental drivers of these behavioral changes in feeding humpbacks.

“While humpback whales in the Southern Hemisphere are known for annual migrations between the summer high-latitude Southern Ocean feeding grounds and the winter mating and calving grounds in subtropical coastal waters, feeding in such dense packs is unprecedented,” said Dr. Olaf Meynecke, a whale researcher and Manager of the Griffith Whales and Climate Program.

Dr. Subhra Prakash Dey from the Department of Oceanography UCT said the formation of whale super-groups in recent years suggested a potential change in oceanographic or ecological characteristics which provide the conditions for this new feeding strategy.

“Through the development of fine scale ocean models our team was able to reveal these oceanographic and ecological changes in the area, the Southern Benguela Upwelling System (SBUS) off South Africa, that had previously remained hidden,” Dr. Meynecke said.

Understanding how “marine snow” acts as a carbon sink

Hitchhiking bacteria dissolve essential ballast in “marine snow” particles, which could counteract the ocean’s ability to sequester carbon, according to a new study.
Photo Credit: MIT News; iStock
(CC BY-NC-ND 3.0)

Scientific Frontline: Extended "At a Glance" Summary: Marine Snow and Carbon Sequestration

The Core Concept: Marine snow is a continuous shower of organic dust and detritus that falls from the upper layers of the ocean to the seafloor, acting as a vital "biological pump" that transports and stores atmospheric carbon in the deep ocean.

Key Distinction/Mechanism: While it was previously assumed that the calcium carbonate ballast weighing down marine snow remained intact until reaching profound depths, recent findings reveal a microscale disruption. Bacteria hitchhiking on these sinking particles consume organic material and excrete acidic waste, which dissolves the calcium carbonate ballast, slowing the particles' descent and prematurely releasing carbon dioxide back into the shallow ocean.

Major Frameworks/Components: 

• The Biological Pump: The overarching macroscale process by which phytoplankton absorb atmospheric carbon dioxide and convert it into sinking organic matter and calcium carbonate.
• Microbial Dissolution Feedback: The microscale localized chemical reaction where bacterial metabolic waste creates an acidic environment that erodes inorganic calcium carbonate.
• Sinking "Sweet Spot" Dynamics: A hydrodynamic framework demonstrating that dissolution peaks at intermediate sinking speeds, where bacteria remain sufficiently oxygenated but their acidic waste is not flushed away too rapidly by surrounding currents.
  

Heatwaves like ‘the Blob’ could decrease role of ocean as carbon sink

A major two-year heatwave may have temporarily dampened the Pacific’s ability to sequester carbon, according to research from the University of British Columbia and University of Southern Denmark. Credit: Jody Wright

Researchers have found the two-year heatwave known as ‘the Blob’ may have temporarily dampened the Pacific’s ‘biological pump,’ which shuttles carbon from the surface ocean to the deep sea where it can be stored for millennia.

Canadian and European researchers, in collaboration with the U.S. Department of Energy Joint Genome Institute, conducted a large-scale study of the impact of one of the largest marine heatwaves on record – colloquially known as the Blob – on Pacific Ocean microorganisms. Their observations suggest that it’s not just larger marine life that is affected by abrupt changes in sea temperature.

“Heatwaves such as the Blob may decrease the ocean’s biological role as a carbon sink for fixed atmospheric carbon,” said Dr. Steven Hallam (he/him), a microbiologist at the University of British Columbia and author of the paper published in Nature Communications Biology.

This ‘biological pump’ process is an important mechanism for buffering the impact of human activity on Earth’s climate, said co-author Dr. Colleen Kellogg (she/her), a research scientist with the Hakai Institute. “The ocean is a huge global reservoir for atmospheric carbon dioxide. If marine heatwaves reduce the capacity for carbon dioxide to be absorbed into the ocean, then this shrinks this reservoir and leaves more of this greenhouse gas in the atmosphere.”

Retreating Glaciers May Send Fewer Nutrients to the Ocean

Northwestern Glacier in Alaska has retreated approximately 15 kilometers (nine miles) since 1950.
Photo Credit: Kiefer Forsch/Scripps Institution of Oceanography.

The cloudy, sediment-laden meltwater from glaciers is a key source of nutrients for ocean life, but a new study suggests that as climate change causes many glaciers to shrink and retreat their meltwater may become less nutritious. 

Led by scientists at UC San Diego’s Scripps Institution of Oceanography, the study finds that meltwater from a rapidly retreating Alaskan glacier contained significantly lower concentrations of the types of iron and manganese that can be readily taken up by marine organisms compared to a nearby stable glacier. These metals are scarce in many parts of the ocean including the highly productive Gulf of Alaska, and they are also essential micronutrients for phytoplankton, the microorganisms that form the base of most marine food webs.