Phytoplankton – Concept, diet and importance

We explain what phytoplankton is and how this organism feeds. Also, why is it so important and what is zooplankton.

Phytoplankton - plankton
Phytoplankton are made up of bacteria, cyanobacteria, algae, and diatoms.

What is phytoplankton?

Let’s start by defining plankton: an enormously diverse set of microscopic organisms that float in the fresh and salty waters of the planet, extremely abundant in the first 200 meters of water depth and a source of food for many marine species.

While the plankton It is made up of numerous forms of plant, animal and protist lifeIt is traditionally classified into two: phytoplankton and zooplankton. The first is autotrophic plankton, and the second is heterotrophic plankton; that is, the first leads a nutritional life similar to plants, while the second leads a nutritional life similar to animals. This, of course, does not mean that they are strictly speaking plants and animals, so this classification, although accepted, is not entirely accurate.

Phytoplankton are mostly photosynthetic, so proliferates in the surface regions of waters, where it has access to sunlight and where there are the most abundant mineral salts (up to 30 meters deep). They are so numerous that they are responsible for the production of 50% of the molecular oxygen that allows and sustains life on Earth. In fact, many of the species that make up phytoplankton date back to the times of the Great Oxidation, the remote geological period when the atmosphere was first filled with oxygen.

Broadly speaking, phytoplankton is made up of bacteria, cyanobacteria (blue-green algae), algae and especially diatoms, which are microscopic eukaryotic organisms with golden-yellow pigments.

In recent times, phytoplankton levels in rivers, lakes and oceans have dropped alarmingly, in principle due to the increase in the levels of ultraviolet radiation that filters through the atmosphere. In regions less protected by the ozone layer, plankton productivity has fallen by between 6% and 12%, which has raised alarm from environmental sectors.

What do phytoplankton feed on?

Phytoplankton - plankton
Photosynthesis is the main metabolic activity of phytoplankton.

Phytoplankton is autotrophic, that is, make or synthesize their own food from non-organic sources, just as plants do. In fact, photosynthesis is its main metabolic activity, taking advantage of sunlight and water to make useful biomolecules, releasing molecular oxygen in the process (O2).

Other species of phytoplankton carry out chemosynthetic processes, that is, the use of chemical energy generated by inorganic chemical reactions. Either way, we can say that phytoplankton feed on inorganic matter and external energy sources, from the environment.

Importance of phytoplankton

These microscopic little creatures they are the very basis of the marine food chainas they provide food for microscopic organisms, fish, crustaceans and other kinds of underwater life, some as large as blue whales (which filter it from the water with their long bales). In that sense, they are producer organisms, which occupy the first link of the food pyramid.

On the other hand, phytoplankton is, as we said before, responsible for the highest oxygenation rate on the planet, producing as much or more of this molecular gas than plants themselves. That means that without them, the oxygen levels in the waters and air of the atmosphere would drop, making the world less suitable for life as we understand it, and making us even more dependent on plants to manufacture. the oxygen that animals breathe.

Phytoplankton and zooplankton

Zooplankton - Plankton - Phytoplankton
The zooplankton would come to be a collection of diverse microscopic consumers.

We have explained at the beginning the distinction between phytoplankton (autotrophs, producers) and zooplankton (heterotrophs, consumers)Although these names would not be the most correct to differentiate them from a metabolic point of view. A second distinction would recognize holoplankton (organisms that are part of plankton throughout their lives) and meroplankton (organisms that only make up plankton during one stage of their life).

While phytoplankton could be understood as microscopic and photosynthetic aquatic beings, zooplankton would become a collection of diverse microscopic consumers, among which are parasites, larvae of larger organisms, single-celled eukaryotes and other life forms close to the animal kingdom.