One of the most important organisms for life in aquatic environments is phytoplankton. It is a type of pelagic autotrophic organism that is incapable of opposing the action of currents and, therefore, is widespread in almost all aquatic places on the planet. The vast majority of these organisms are unicellular and are carried by ocean currents. They are important for the development of ecosystems and biodiversity since they are primary producers. This means that they are the basis of the food webs of aquatic environments.

In this article we are going to tell you about all the characteristics and importance of phytoplankton.

Main features

Since these organisms are the base of the food chain, they are found in almost all bodies of water on the planet and throughout the entire water column. The densities of the populations fluctuate with time and some variables that affect the marine environment. These organisms can form very dense temporary aggregates that are known as blooms, turbid or bloom. All these blooms, where phytoplankton are largely abundant, have the ability to modify the physical and chemical conditions of the water where they are found. In this way, we find waters that are richer in nutrients and with greater biodiversity and other poorer ones.

They are organisms of the Chromist kingdom , so they are known to be eukaryotes. One of their main characteristics is that they present chloroplasts with type a and c chlorophyll. It is thanks to this chlorophyll that it can carry out photosynthesis and serve as food for other animals in the ecosystem. They are unicellular organisms and microscopic in size. They cannot defeat currents so they spread widely throughout all aquatic ecosystems where they are found.

In order to photosynthesize and feed, it needs energy from the sun. Therefore, although it extends throughout the entire water column, it is more abundant in the pelagic part. That is, in the most superficial zone of the water there is a higher concentration of phytoplankton. In order to survive, it has a dependence on light that limits it to living in the area where sunlight penetrates into aquatic environments. Beyond these areas, near the seabed, their concentration is very low or null.

Main representatives of phytoplankton

The main representatives of phytoplankton are diatoms, dinoflagellates and coccolithophores. Let’s analyze what its main characteristics are:

  • Diatoms: they are unicellular organisms that sometimes act as colonial organisms. They are characterized by having a frustule that is a fairly hard cell wall. It is made up mainly of silica. Diatoms inhabit almost all aquatic places and even those that are not aquatic but are very humid.
  • Dinoflagellates: They are also single-celled organisms that may or may not form colonies. Most of them are photosynthetic organisms and have type a and c chlorophyll. The difference between dinoflagellates and diatoms is that there are also some that are heterotrophs and others that are autotrophs. This causes that there are some of them that need to obtain food from another organism. Most of them are marine, although some live in fresh water. Most of them are free-living although there are also some species that are associated with other animals such as corals. Its main characteristic is to present two unequal flagella. With these flagella they can perform oscillatory movements and move in the water column.
  • Cocolithophores: these are unicellular microalgae that are covered by structures of calcium carbonate. These structures acquire a scale shape that makes them have a peculiar shape. They only live in marine environments and do not present a scourge to be able to move.

Other components of phytoplankton are cyanobacteria. These are prokaryotic organisms that have the ability to photosynthesize but only have chlorophyll a. They also have the ability to fix nitrogen and convert it to ammonia. Their main habitat is lakes and lagoons, although they can also be found in oceans and other humid environments.

Importance of phytoplankton

Phytoplankton plays a great role in ecological life and its ecosystem balance. The main function of these organisms is to sustain life and the rest of the relationships in the food chain. This means that an excess of marine pollution that causes the disappearance of phytoplankton or its reduction can affect the entire ecosystem as a whole. They are capable of transforming energy from the sun, carbon dioxide, and inorganic nutrients into organic compounds and oxygen. In this way, not only life in the aquatic environment is sustained, but the planet in general.

The entire set of phytoplankton represents about 80% of the organic matter of the entire planet. This organic matter is the food of an immense variety of fish and invertebrates. In addition, it not only helps to sustain life but is responsible for producing more than half of the planet’s oxygen. It is due to its ability to photosynthesize. These organisms are also known to be a critical part of the carbon cycle.

Phytoplankton also have other uses in industrial and clinical settings. Many species of microalgae are used in aquaculture to feed larvae of some species of fish and shrimp in rearing. Numerous studies have been conducted on the potential of microalgae as a biofuel. This can help generate certain types of fuels to alleviate the effects of climate change and global warming.

Another use of phytoplankton is in natural medicine, cosmetics and as biofertilizers in many types of hydroponic agriculture. Finally, the clinical importance of phytoplankton is based on the availability of nutrients that it has in a certain place and that is used by other microorganisms through accelerated cell multiplication. Some species of phytoplankton such as dinoflagellates can produce toxins and their blooms are known by the name of red tides.

Phytoplankton nutrition

Let’s see what the nutrition of phytoplankton. It is quite varied, although photosynthesis is the common factor among all groups. The type of diet that some organisms present are those that are capable of generating their own food. In the case of some organisms that make up phytoplankton, we see that sunlight is used to transform inorganic compounds into organic matter that is used by themselves.

Another autotrophic process is that carried out by cyanobacteria. These are capable of fixing nitrogen and converting it into ammonia.

On the other hand, we have heterotrophy. It is a style of eating in which organisms depend on organic matter that is already made. In this way, with an organic matter already made, they can obtain their food. Among the most basic examples of heterotrophy we have predation, parasitism, and herbivorous feeding. Some organisms belonging to phytoplankton present this type of nutrition. One of them are dinoflagellates. They have some organisms that are capable of preying on other dinoflagellates, diatoms, and even other organisms.

Finally, we are going to analyze the mixitrophy. It is a unique condition that some organisms that are able to obtain their food through both processes. Some species of dinoflagellates are capable of combining obtaining food through photosynthesis with heterotrophy.

Phytoplankton reproduction

These organisms need to reproduce in order to increase their range and habitat. Organisms have a wide variety of reproductive forms. This is mainly due to the fact that there is a diversity of different species and groups. Despite this, if we divide reproduction there are broad features, we see that there are two main types: asexual and sexual reproduction.

Asexual reproduction is one in which the descendants were only the genes of a single parent. The gametes are not involved here. There is also no variation of the chromosomes and it is the one that occurs more commonly in organisms that are unicellular. As we have mentioned before, most of the organisms belonging to phytoplankton are unicellular organisms. Among the centers of sexual reproduction we have binary fission and budding. In the first, the DNA multiplies by the progenitor cell and after a process called cytogenesis, the cytoplasm division occurs. This gives rise to two or more daughter cells.

The second asexual reproduction process is budding. Here there is the formation of a bud that sprouts from the adult and grows on it. It feeds on the nutrients of the parent and when the individual has already reached a certain size, it starts independently.

Now we are going to see what sexual reproduction is like in phytoplankton. An offspring is obtained from the combined genetic material of two sex cells or gametes. They can come from both the same parent and a different parent. Some species of phytoplankton undergo sexual reproduction such as dinoflagellates under certain environmental pressure.

In this type of reproduction, a zygote is formed thanks to the fusion of two individuals. Another example of sexual reproduction is diatoms. This process occurs mitosis and one like daughter cells ends up being smaller than the progenitor cell. As this process actually takes place, the size of the daughter cells decreases to a sustainable natural minimum. From there, the process of sexual reproduction begins to be able to restore the normal size of the cells of the population.

Phytoplankton and zooplankton

We must know that plankton in general is composed of both types of organisms. We have already talked about what phytoplankton is and how important it is to the planet. Now we are going to describe what zooplankton is and what its importance and differences are. These are aquatic animals that are microscopic or macroscopic in size. As with the small plants that make up phytoplankton, they also live suspended in the water column.

They can consist of adult individuals with small larvae and eggs. Among the most abundant organisms within zooplankton we find copepods, cladocerans, rotifers, cnidarians or ketognaths, among others. Also keep in mind that numerous species of fish and mollusks are also planktonic. However, they are only so during their embryonic stage. It has the ability to grow and develop to the point of being able to swim freely. We remember that both phytoplankton and zooplankton cannot resist water currents and are washed away. Their swimming ability is limited.

Water we see the example of jellyfish as part of zooplankton. We take into account that the jellyfish are already larger and, even if they are, they are dragged adrift by the ocean currents. Keep in mind that zooplankton obtain their energy by ingesting other organisms. They can also acquire energy through the consumption of phytoplankton, other smaller zooplankton or bacterioplankton.

Perhaps the main difference between these types of organisms may be that there are no autotrophic organisms in zooplankton. They are animals that are fed in one way or another but in heterotrophy. One of the variables by which the zooplankton present in an area can change and is the phytoplankton itself. We know that, depending on the changes in these plant organisms, the complete composition of the animals that make up the zooplankton can be modified. All this can have consequences on the recruitment of fish and the sedimentation rate of organic matter.

In turn, all this can affect the concentration of oxygen present on the seabed. There are numerous studies of the composition, abundance and distribution of zooplankton that allow describing the trends of this type of community over two years. Thanks to this, a great deal of information can be learned about the evolution of species in the aquatic environment.

I hope that with this information you can learn more about phytoplankton and its importance.

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