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Decline of Diatoms due to Ocean Acidification



Introduction

Diatoms, a type of algae, serve as a keystone species of the marine ecosystem. As producers, they serve as the foundation to the oceanic food web, feeding plankton, fish and more. These organisms are typically unicellular or colonial, and they thrive in environments that are rich with carbon dioxide, outcompeting other types of algae such as seaweed. Their incredible ability to sequester atmospheric CO2 makes them vital carbon sinks in a world with devastatingly high levels of greenhouse gasses. Annually, they are able to remove 10 to 20 billion metric tons of inorganic carbon from the atmosphere to produce organic compounds (Karlusich et al., 2021). They aid in the transport of carbon dioxide to deep sea waters, which helps regulate the climate (Helmholtz Centre for Ocean Research Kiel (GEOMAR), 2022). The increased global temperatures has resulted in a phenomenon known as ocean acidification, as dissolved CO2 raises seawater pH levels, harming thousands of marine species as a result. Diatoms were previously thought to be unaffected due to their unique structure, but evidence points to their declining population.



Figure 1. Assorted Diatoms through a microscope (Taylor, 1983).


Structure

A diatom’s defining feature is their inorganic cell wall, made from silica, a compound consisting of silicon and oxygen. This glass-like shell is also referred to as a frustule, and often creates intricate patterns in a circular or elongated shape (The Editors of Encyclopaedia Britannica, 2023). Since ocean acidification mainly affects calcifying organisms, diatoms were thought to be resistant to the rising pH levels. Organisms such as mollusks and urchins rely on calcium carbonate to construct their shells, and that ability is limited by increased ocean acidity, but silica had no such weakness. Yet research from the GEOMAR Helmholtz Centre for Ocean Research Kiel and other institutions present new findings which threaten the wellbeing of diatom populations (2022). Ocean acidification results in a decreased rate of dissolution for the silica shells, which causes them to sink to deeper layers of water before being chemically dissolved. Thus, the compound is not accessible to other diatoms near the surface level, despite the need for a supply of silicon to build their shells. As a result, the diatom population is at risk of decreasing by as much as 10% by the end of the twenty-first century, which could have catastrophic impacts on the ecosystem (Helmholtz Centre for Ocean Research Kiel (GEOMAR), 2022).


Impacts of Declining Population


Not only are diatoms an important food source for a variety of marine life, but they also regulate the carbon cycle. These autotrophic organisms use sunlight to photosynthesize, which allows them to fixate dissolved carbon dioxide in the water to form organic compounds, releasing oxygen as a byproduct. It is one of the main aquatic producers that allow the ocean to be known as a carbon sink. Additionally, it accounts for over 40% of marine biomass, and is staple in the diets of snails and other small fish (Harvey et al., 2019). Even their fossilized remains are beneficial for industrial use. Diatomaceous earth, a powder made from a combination of sediment and diatom shells, can be used to improve one’s health due to its high silica content. It also serves as a filter to remove unwanted materials in drinking water, an insecticide, a type of insulation, and even as a base in dynamite (WebMD, n.d.).



Figure 2. Diatomaceous Earth under an electron microscope (Siodłak, 2015).



Figure 3. Diatoms and the carbon cycle (Karlusich et al., 2021).


Prevention

Humanity’s irresponsibility and disregard for the environment has accelerated global warming to a point where it is impossible for nature to recover on its own. Diatoms play a vital role in the marine ecosystem, climate regulation, and human industry. Studies show that if humanity’s current destructive behaviour continues, the decrease in population may not be limited to 10%. In fact, increasing greenhouse gas emissions may result in losses of up to 26% by 2200, which is over a quarter of the current population (Helmholtz Centre for Ocean Research Kiel (GEOMAR), 2022). It was wrongful to assume that they experienced no effects of ocean acidification, simply because it is not a calcifying organism. The biosphere continues to prove that if climate change continues, all of Earth’s unique flora and fauna are in grave danger.

[References] Decline of Diatoms due to Ocean Acidification
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