Diatoms: the microscopic algae and “lungs” of the Earth that you should know

For many, it may come as a surprise, but the truth is that most of the annual oxygen production on our planet – between 50% and 85% – does not come from terrestrial forests, but from the ocean. Phytoplankton, a set of millions of microorganisms that are present in the waters that surround the five continents, is responsible for carrying out a photosynthetic process in which it is estimated that about 10 gigatons of carbon from the atmosphere are “buried” in the depths of the ocean every year. 

Although of all the species that make up phytoplankton, around 80% would correspond to diatoms (Bacillariophyta), which are unicellular microscopic algae that can be found floating freely in the water or attached to a substrate. In fact, if you’ve ever gone to the ocean or lake and swallowed some water, you’ve probably swallowed quite a few!

According to José Luis Iriarte, the scientist from the High Latitude Marine Ecosystem Dynamic Research Center (IDEAL) and academic from the Aquaculture Institute of the Austral University of Chile (UACH), the abundance of diatoms in the ocean is so widespread, that if a sample of 10 ml of seawater is taken – which is equivalent to two teaspoons of tea – at least 50 species could be found there. And if the sampling were carried out for a full year, at least 200 species could be identified from the same two teaspoons. And they would not only be found in the oceans since they can also be found in lakes, rivers, and even in mosses.

“These microorganisms are responsible for 50% of the oxygen found in the ocean and are present in any aquatic system, and in any habitat. We can find them in the ice, either in the glacier or in the ice formation in Antarctica. There, they are below the ice and survive the winter by clinging to it, until summer arrives, when the snow melts and they bloom again. You can also find them in the lagoons and salt flats of the altiplano, or in geysers since they are capable of living in extreme temperature environments ”, he added.

An organism with a wide presence worldwide, and that can even be seen from space due to its large number of specimens that reflect light in a different way from the rest of the ocean; this, despite the fact that it only reaches a size of a quarter of the diameter of a human hair. The importance of diatoms is such that it could be said that out of every five breaths we take, at least the oxygen in one of them can be entirely attributed to these microorganisms.

Striking shapes, transparent like glass

Diatoms are made up of a soft body or “naked cell” where their genetic material is found, but in addition to that basic structure, one of the most striking aspects that characterize them is their cell wall, which is based on silica instead of one based on carbon, which is more common in other species of algae or terrestrial flora.

Silicon, the material that mainly makes up these walls, is a chemical element that corresponds to a semimetal or “metalloid”, which is very present on our planet in the form of silicon dioxide – this means that it is combined with oxygen – contributing to about 75% of the earth’s crust. This element – which is also present in the manufacture of glass, although in a different composition – provides transparency to the cell wall of diatoms, which has earned them the nickname “glass or glass houses” mainly in the press.

“The cell wall of diatoms is made up of silicon in the organic form of silicate. It is like a box, which we call a frustum, and it has an upper part, the epitheca, and a lower part, the mortgage, which fit together. Inside these two parts is the cell. It’s like a jewelry box that fits, ”Pilar Muñoz, a marine biologist and researcher at the Marine Algae Laboratory of the University of Valparaíso, told Ladera Sur.

Although depending on the environment in which diatoms live, the shape of their cell walls changes. According to Iriarte, diatoms are divided into two morphologies: some are centric, which have a volumetric perspective similar to a drum, which would imply that when observed in a microscope they appear circular; and on the other side would be the penned as, which have a more elongated shape similar to an ellipsoid.

Regarding the centric ones, these could be found in the first 25 meters of depth in the ocean, which can also be recognized because they are the ones that most commonly form chains -not being a unique characteristic of them-, which would be a strategy for survival in many ways.

“These microorganisms are chained between the different cells, to form a larger structure that allows greater buoyancy. Since diatoms do not have a structure that allows them to move independently, they need to float in the fluid, be it freshwater or saltwater. This allows them not to settle on the ocean floor, at the bottom of the sea. Furthermore, this is beneficial given that diatoms photosynthesize, and therefore they need to be closer to the sun, which is on the surface ”, indicated Iriarte, who also comments that other buoyancy strategies available to diatoms are the presence of a vacuole of air within its structure, as well as the formation of external structures or “mushrooms” that would allow it to prolong its stay on the surface.

Regarding the penned as, their more elongated structure and with a greater amount of silica would make them heavier than their centric pairs. This is due to the fact that, sometimes, the pen requires a substrate, for example, a rock, in order to survive, and this extra weight would help them to remain “attached” to said surface.

Its surprising transparency, in addition to the large number of shapes that the siliceous walls of the nearly 20,000 documented species of this group of microalgae can adopt – although it is believed that it could reach up to 2 million -, they are so varied and striking that they have I have the nickname “kaleidoscopic”. In fact, according to Muñoz, their peculiar and aesthetic shapes are one of the reasons for the great documentation of species that diatoms have, because, after their discovery, observing them under the microscope became something of a common hobby.

But where does the silicon come from that makes them so unique? According to Iriarte, this element is present in the ocean naturally, but in very deep layers below 1,000 meters in height, at a very great distance from where these microorganisms live, generally associated with euphotic areas – which can reach the first 200 meters. deep -.

So how does this element get to diatoms? According to the researcher, this occurs in two ways. The first is through upwelling systems, where masses of water from deep areas emerge towards the surface, a phenomenon that would occur in relatively few places in the world – and in which Chile is a fortunate country – since according to India at the Marine Conservation Center of the Pontificia Universidad Católica de Chile, occurs mainly on the southern and northwestern coasts of Africa, as well as west of the United States and Chile-Peru.

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