ZOOPLANKTON

 The zooplankton is the plankton made up mainly of animal species that may be present in freshwater or drink . Taking this definition into account, it is essential to know what plankton is to understand the notion.

It is called plankton to the group of very small organisms that move passively through the water, that is, floating. These organisms remain suspended in the aquatic environment, usually at a depth of up to two hundred meters.

Plankton can be divided into the aforementioned zooplankton (composed of those organisms that, as food, ingest organic matter that is already processed) and phytoplankton (also known as plant plankton, their organisms are autotrophic and carry out photosynthesis ).

From this point two very important concepts arise when defining the different types of plankton:

* Autotrophic organisms : are those whose nutrition is based on the ability to synthesize all the substances that are essential for metabolism starting from inorganic substances. In other words, they do not require living beings to feed themselves ;

* Heterotrophic organisms : unlike autotrophs, they do need other living beings to feed themselves, since they carry out a transformation of their organic matter to obtain energy and essential nutrients for their development .

Therefore, we can say that zooplankton is the part of plankton that is characterized by being heterotrophic, and not autotrophic. In zooplankton we find carnivorous, herbivorous and omnivorous organisms. Also, some are kept in symbiosis with algae, while others are parasites.

Regarding the type of reproduction, in zooplankton there are examples of sexuality with alternation of generations and asexual reproduction by bipartition. The size of the individuals gives rise to a classification according to which we have, on the one hand, the protozooplankton , where a portion of the microplankton is found , and on the other, the metazooplankton , which are included in the megaplankton , the macroplankton and the mesoplankton .

Within protozooplankton, organisms are classified according to their locomotion system:

* Zoomastigines have flagella that they use to move around, and that is why they are also called zooflagellates ;

* the sarcodine group has a locomotion system that is based on pseudopodia, extensions of the cytoplasm that can also serve to capture food;

* Ciliaphores move with the help of cilia, elongated hair-like appendages

In the case of metazooplankton, the classification is based on the time they spend in the plankton:

* holoplankton stay in plankton for their entire life. In this group we find chitinous zooplankton (arthropods, ketognaths and annelids) and also gelatinous (chordates, mollusks, ctenophores and cnidarians);

* Meroplankton only remain in plankton for part of their development.

Among the species that make up zooplankton, there are various protozoa ; small crustaceans; fish in their juvenile stage; and larvae of mollusks, sponges and other types of animals. Zooplankton usually travel between one hundred and four hundred meters per day, moving from above to below in the water. The usual thing is that, at night, it approaches the surface to obtain food. When the sun shines, instead, it dives to avoid the sun's rays.

Members of zooplankton eat phytoplankton, bacteria, and even other members of zooplankton. The food chain, in turn, marks that zooplankton are eaten by fish, crustaceans and echinoderms. Humans, for their part, also consume zooplankton, although they also use it for other commercial purposes.

It is important to mention that certain organisms combine photosynthesis with the consumption of organic matter: in this way, they can be incorporated into phytoplankton and zooplankton. There is also meroplankton: beings that are part of plankton in a vital stage and then join other types of communities.