Marine Phytoplankton Are Far More Adaptable to Future Climate Change, According to Scientists

An international team of scientists released a paper in Science Advances that gives compelling evidence that marine phytoplankton are significantly more adaptable to future climate change than previously anticipated.

Metabolic hack makes ocean algae more resilient

(Photo : DANIEL SLIM/AFP via Getty Images)

Combining data from the long-term Hawai'i Ocean Time-series program with new climate model simulations run on one of South Korea's fastest supercomputers, the researchers discovered that a mechanism known as nutrient uptake plasticity allows marine algae to adapt and cope with nutrient-poor ocean conditions expected to occur over the next decades as a result of upper ocean global warming, as per ScienceDaily.

Phytoplankton is microscopic algae that float at the ocean's surface and constitute the foundation of the marine food chain.

While photosynthesizing, these algae consume nutrients (such as phosphate and nitrate), absorb dissolved carbon dioxide, and exhale oxygen, accounting for approximately 50% of the oxygen humans breathe.

Comprehending how marine algae will adapt to global warming and the consequent loss in nutrients in upper ocean waters is therefore critical for understanding our planet's long-term habitability.

The worldwide yearly phytoplankton production rate is very unknown for the next 80 years.

The newest Intergovernmental Panel on Climate Change (IPCC) study reveals an uncertainty of -20% to +20%, implying that phytoplankton will increase or decrease in the future.

The higher layers of the water are more affected by global warming than the deeper levels.

Warmer water is lighter, therefore the upper ocean will become more stratified in the future, reducing nutrient mixing from the subsurface into the sunlit layer, where phytoplankton lives.

Previous research revealed that the predicted future depletion of nutrients near the ocean's surface will result in a significant decrease in phytoplankton production, with extensive and perhaps catastrophic implications on both marine ecosystems and climate.

However, according to new research published in Science Advances, this may not be the case.

New studies of upper ocean phytoplankton data from the Hawai'i Ocean Time-series program reveal that productivity may be sustained even in severely nutrient-depleted circumstances.

"Under such conditions, individual phytoplankton cells can substitute phosphorus with sulfur, and on a community level, one might see further shifts towards taxa that require less phosphorus," said David Karl, a co-author of the study, Professor in Oceanography at the University of Hawai'i, and co-founder of the Hawai'i Ocean Time-series Study program, to illustrate the concept of phytoplankton plasticity.

Further evidence for adaptability comes from the fact that in subtropical locations with low nutrient concentrations in surface waters, algae use less phosphorus per quantity of carbon stored in their cells than the global average.

To investigate how this unique metabolic "hack" may affect global ocean productivity over the next few decades, the researchers performed a series of climate model simulations on their supercomputer Aleph using the Community Earth System Model (version 2, CESM2).

The scientists were able to qualitatively duplicate prior model estimates of an 8% drop in global production by turning off phytoplankton plasticity in their model.

However, turning on the plasticity parameter in their model in a way that matches the data around Hawai'i for the previous three decades results in a 5% rise in worldwide production through the end of the century.

"However, regionally, these potential productivity variations might be substantially bigger, reaching up to 200% in subtropical regions," says Dr. Eun Young Kwon, first author of the study and a researcher at Pusan National University's IBS Center for Climate Physics in South Korea.

With this increased productivity, the ocean may absorb more CO2 from the atmosphere and eventually sequester it beneath the ocean's surface.

Also Read: Phytoplankton Under Antarctic Sea Ice Could be Supporting a Whole Ecosystem

Phytoplankton and its impact on water quality

Phytoplankton abundance is often high in aquaculture ponds due to high concentrations of nutrients from fertilizer or feed inputs, as per Global Seafood.

Phytoplankton absorbs nutrients from the water and eliminates ammonia nitrogen from the water, which is especially crucial in reducing amounts of this potentially hazardous compound.

Phytoplankton has a number of different indirect effects on water quality.

For photosynthesis, phytoplankton extract carbon dioxide from the water. Carbon dioxide is acidic in water, and when phytoplankton removes carbon dioxide for photosynthesis, the pH of pond water rises over the day.

When phytoplankton removes all of the carbon dioxides from the water, bicarbonate is utilized as a carbon source in photosynthesis.

Many aquatic plants have a physiologic mechanism that allows them to extract one carbon dioxide molecule from two bicarbonate ions while releasing one carbonate ion into the water.

Because carbonate ion combines with water to raise pH, pH rises during photosynthesis even after all dissolved carbon dioxide has been eliminated.

In most ponds, bicarbonate is the primary source of alkalinity.

Despite this, overall alkalinity in pond water does not decrease when phytoplankton consumes bicarbonate in photosynthesis.

This is because one carbonate ion contributes the same amount to alkalinity concentration as two bicarbonate ions.

Alkalinity buffers water against pH shift, and in low alkalinity waters, particularly those with alkalinity below 20 mg/L, pH can rise to stressful or deadly levels for aquaculture species.

Liming is recommended in aquaculture ponds to raise total alkalinity over 40 to 50 mg/L.

Related article: Scientists Want Phytoplankton to Take Over the Waters, Induce Increased Carbon Cycling, Fight Climate Change