Rising ocean acidity is threatening the population of the most common type of plankton, known as diatoms, one of the main oxygen producers on the planet and the primary food source for all marine life. Despite previous beliefs that diatoms actually benefit from ocean acidification, new research from the Helmholtz Centre for Ocean Research (GEOMAR) shows that diatom populations are extremely vulnerable to the effects of ocean acidification. Continue reading for a summary of the paper’s findings.

Background Information: How Ocean Acidification Affects Diatoms

Full Study: Decline of diatoms due to ocean acidification (Nature, May 2022).

how does ocean acidification affect diatoms research — Researchers studying the effects of ocean acidification on diatom populations
Source: Ulf Riebesell/GEOMAR/European Geosciences Union

How Ocean Acidification Reduces Diatom Populations

In past years, scientists believed that diatoms are less affected than other marine organisms by the effects of ocean acidification. This was because diatoms rely on silica minerals to build their shells, rather than calcium carbonate, a substance that many other marine organisms rely on to build their shells and that is reduced by ocean acidification. In fact, some scientists previously argued that ocean acidification aids diatoms by increasing their ability to photosynthesize, and thus increasing diatom populations’ growth.

But, in a recent analysis, scientists explain how ocean acidification may reduce the population of diatoms at an alarming rate. Here’s what you need to know about it.

The study researched the effects of ocean acidification on the dissolution of the silicon shell of diatoms. The results show that acidified seawater significantly slowed the ability of diatoms to dissolve their silicon shells, ultimately leading to a lowered ability to gain nutrients through photosynthesis.

The most common negative impact of ocean acidification on shell-forming marine species using calcium carbonates, such as oysters, clams, mussels, and corals, is a reduction in their capacity to form shells due to a lack of carbonate ions in more acidified seawater. While this chemical imbalance was not believed to affect diatoms due to their silicon-based shells, ocean acidification actually threatens diatoms in another way.
GEOMAR Helmholtz Centre for Ocean Research Kiel researchers used data from huge test tubes known as Mesocosms. These tubes were placed in different ocean biomes all around the world. Mesocosms can contain a large volume of ocean water inside, allowing researchers to manipulate the water parameters, such as increasing or decreasing the acidity level without harming the ocean ecosystem outside.
Using an Earth system model, the researchers utilized the collected data to simulate the negative effects of ocean acidification on diatoms in the future, on a worldwide scale.
Researchers discovered that acidified seawater slows the ability of diatoms to dissolve their silicon shells, which forces them to sink into the deeper parts of the ocean. Because of this, the abundance of diatoms on the ocean surface is lowered.
Researchers concluded that since diatoms needed to be at the surface water to get light to renew their shells, forcing them to sink may significantly decrease their population around the world at an alarming rate.

mesocosm - ocean acidification diatoms study — A photo of Mesocosm underwater
(Source: © Ulf Riebesell GEOMAR/University of Tasmania, IMAS)

diatom life cycle - ocean acidification — A comparison of the diatom life cycle today (a) and in the future, the year 2200 (b), as simulated in the study.
(Source: © Nature)

Sources:

“Decline of diatoms due to ocean acidification. Study shows unexpected negative impact by CO2 on important plankton group” Science Daily, May 25, 2022

https://www.sciencedaily.com/releases/2022/05/220525182619.htm

“Research reveals ocean acidification is triggering a decline in diatom” UTAS, IMAS, May 31, 2022

https://www.imas.utas.edu.au/news/news-items/research-reveals-ocean-acidification-triggering-decline-in-diatoms#:~:text=%E2%80%9CThe%20reason%20for%20this%20decline,needed%20to%20form%20new%20shells.%E2%80%9D

Ocean acidification occurs when the pH level of seawater decreases, which is most frequently caused by the ocean absorbing excess CO₂ from the atmosphere. Ocean acidification has negative effects on a variety of ocean ecosystems and life forms, including diatoms, a type of phytoplankton characterized by glass-like cell walls made of silica.

This article will explain how diatoms are affected by ocean acidification, and will discuss the importance of diatoms to ecosystems and people.

Background information: Ocean Acidification Infographic

Table of Contents

What Are Diatoms?

How Are Diatoms Affected by Ocean Acidification?

The Importance of Diatoms

The Importance of Diatoms to the Ecosystem

The Importance of Diatoms to People

What Are Diatoms?

Diatoms are one of the two common types of phytoplankton. They are found in bodies of water such as the ocean, rivers, lakes, and ponds, as well as in mud and moist soils. Diatoms are commonly recognized by their transparent glass-like cell walls made out of silica acids (a type of mineral) that are dissolved in water. Just like corals and other marine plants, diatoms photosynthesize in order to survive, which is why sunlight and carbon are essential to their survival. Diatoms also play a vital role in transferring atmospheric carbon to the deep ocean, which helps to prevent global warming and reduce ocean acidification.

To give you a better grasp, here is a short video explanation and microscopic footage of diatoms by MicroBiome:

How Are Diatoms Affected by Ocean Acidification?

Despite their small size, diatoms play an important role in ocean ecosystems and studies are revealing the risk ocean acidification poses to their wellbeing. Diatoms rely primarily on CO₂for their photosynthesis, so the ocean’s increased absorption of CO₂that causes ocean acidification has a large impact on the creatures. Here are some of the effects of ocean acidification on diatoms.

Ocean Acidification Could Increase the Growth of Diatoms

According to a 2019 study, high CO₂levels due to ocean acidification could increase the metabolism and growth of diatoms. This is because diatoms rely on CO₂as their source of energy in photosynthesis. However, the study’s results are still being debated and there is no final agreement on how these factors would affect the diatom community, nor how diatoms will continue to adapt to the acidifying ocean.

Ocean Acidification Slows the Development of Silica Cell Walls

ocean acidity ph scale - diatoms ocean acidification

Diatoms build their silica cell walls to protect themselves against predators such as krill. The cell wall is an important factor for their survival. According to a 2019 study published in Nature, exposure of diatoms to ocean acidification could slow their development of silica cell walls. The study reveals that even when the ocean pH level drops to 7.84 (compared to today’s pH of 8.1), the development of diatom’s silica cell walls reduces. Not only can this affect the ability of diatoms to survive, but it can create an imbalance in the ocean’s silica levels. Even small shifts in ocean acidity can have major impacts.

Ocean acidification may also impact the ability of diatoms to dissolve their shells, leading them to sink into the deep ocean. This reduces their population by making it difficult for them to get light from the surface, reducing their ability to photosynthesize to survive.

Ocean Acidification Could Alter the Efficiency of Diatoms’ Transport OF CO₂to the Deep Ocean

Diatoms play a big role in carbon sequestration. When they die, diatoms sink to the deep ocean with the help of their silica cell walls that serve as a weight and stabilizer. This process works to transport all the CO₂ the diatoms have absorbed to the ocean’s depths, thus sequestering it in the deep ocean and removing it from the atmosphere. However, the same 2019 Nature study discussed above implies that due to the slow development of silica cell walls induced by exposure to ocean acidification, the ability of diatoms to transport CO₂to the ocean’s depths might be negatively affected. Without the carbon sequestration services of diatoms, global warming could accelerate and may cause larger ecological problems, including worsening ocean acidification.

The Importance of Diatoms

Despite their microscopic size, diatoms play a massive global role in making marine and terrestrial ecosystems habitable for both people and wildlife. However, the threat of ocean acidification may put diatoms under new stressors that might affect the services they provide. Here are some of the ways diatoms are important to ecosystems and people.

The Importance of Diatoms to the Ecosystem

Primary Food Provider

Diatoms are at the bottom of the food chain. They serve as food to larger organisms like zooplankton, krill, algae eater fishes, snails, and more. These larger organisms flourish because of the abundance of diatoms. Even larger marine animals depend on the organisms that rely on diatoms. For example, the whale’s primary diet is krill. Without diatoms, krill would not be able to survive. If there are not enough krill to sustain the whales, it could cause starvation and ultimately decline in whale populations.

This hypothetical breakdown of the food chain shows the importance of diatoms as the primary food source in the food chain. Any damages to diatoms caused by catastrophic events such as ocean acidification would have a significant impact on all species who rely on their services, from the smallest krill to the largest mammal on the planet.

Natural Carbon Sink

Diatoms are considered a natural carbon sink, as they absorb up to 20 billion tons of atmospheric carbon annually. Diatoms convert atmospheric carbon into organic carbon as they absorb it through photosynthesis. When they die, they carry the stored carbon down as they sink to the ocean floor. This carbon-absorbing ability has a significant impact on mitigating global warming and climate change.

diatoms carbon cycle - diatoms ocean acidification — *Diatoms carbon cycle*
*Source:* *Frontiers in Plant Science*

The Importance of Diatoms to People

Major Oxygen Supplier

Since diatoms photosynthesize, they contribute significantly to the world’s supply of oxygen. In fact, according to the most recent data, diatoms are responsible for 25% of the global oxygen supply. Without diatoms, all species that rely on oxygen, including humans, may suffer from negative health complications due to lower oxygen supply.

Supplier of Bio-Products

Diatoms not only supply oxygen but they can also be utilized in creating bio-products, products made from natural, renewable materials. According to a recent study, diatoms can produce sustainably manufactured bio-products that could be used as pharmaceuticals that benefit people. This includes the following products:

Lipids
Omega-3 fatty acids
Pigments
Antioxidants
Exopolysaccharides
Sulfated polysaccharides

diatoms microscopic image - diatoms ocean acidification — *Microscopic view of diatoms*
*Source:* *Diatoms.org*

Diatoms can help humans in a variety of ways, including those mentioned above, and there may be many more benefits that science has yet to uncover. We already know how diatoms are affected by ocean acidification, which might alter the services they provide. It is critical to guarantee that these microorganisms continue to thrive, as without them, the Earth may become uninhabitable for humans and other species.