Phytoplankton

The phytoplankton is the subset of aquatic organisms of planktonic communities that are autotrophs (i.e. organisms that produce their own energy reserves with sunlight as the main source of energy). They have photosynthetic capacity and live dispersed in the water. The name comes from the Greek terms, φύτον (phyton, "plant") and πλαγκτος ('plánktos', 'wanderer' or & #39;the one that is tumbling').

General characteristics

Diatoms views through an electronic microscope.

This group includes many beings traditionally considered algae and studied as such (by botany and especially by phycology). Currently, these organisms are classified as bacteria —cyanobacteria (blue-green algae)—, diatoms, dinoflagellates, green algae, and some photosynthetic organisms still classified as Protists.

Although plankton is normally considered to be entirely made up of microscopic organisms, there are some algae, such as certain species of sargassum, that can live freely in the ocean and are also part of the phytoplankton. Many types of phytoplankton, under the right conditions, can form large visible buoyants.

One of the most important groups, due to its abundance and diversity, is that of diatoms, microscopic eukaryotic organisms with yellow-golden pigments and a silica exoskeleton. The nutrition of dinoflagellates is generally autotrophic, but those without pigment ingest the already formed food through their membranes. Several species are parasitic and live at the expense of their host; others live in symbiosis with algae such as zoochlorellae and zooxanthellae, which provide them with food. The cultivation of peridynes is a difficult process, because there is little information regarding their nutritional needs. Another group of socio-ecological and medical importance are cyanobacteria, particularly due to the increase in the frequency and intensity of blooms worldwide that can become toxic.

Ecology

Phytoplankton get their energy through photosynthesis. This is why they live in the part of a body of water as far as sunlight penetrates (the euphotic or photic zone). Worldwide, phytoplankton (marine and non-marine) are responsible for more than half of the photosynthetic activity. In this way, they are organisms responsible for much of the oxygen in our atmosphere; They are good carbon fixers (primary production) and the basis of trophic webs (food webs).

Ecological importance of phytoplankton

Phytoplankton is at the base of the food chain of aquatic ecosystems, since it serves as food for larger organisms; In other words, it carries out the main part of primary production in aquatic environments, especially in marine animals.

But in addition to that, phytoplankton is the original responsible for the presence of oxygen (O₂) in the atmosphere. It is estimated that approximately 50% of atmospheric oxygen has been produced by phytoplankton in the oceans. Oxygenic photosynthesis appeared evolutionarily with cyanobacteria, ancestors other than plastids of eukaryotic algae. For nearly 2 billion years, until the development of land plants, photosynthesis was virtually restricted to the seas. Most of the primary photosynthetic production of the seas, then as now, is attributable to phytoplankton, with a minor part due to benthic organisms.

Flowering or "bloom"

Florecimiento de fitoplancton en las costas argentinas.

Phytoplankton can also be responsible for some ecological problems when they develop too much: in a situation of excess nutrients and favorable temperatures, these organisms can multiply rapidly, forming what is usually called a "bloom" 34;, the most used English word), or also red tides. In this situation, the water turns greenish, but quickly (1-2 days, depending on the temperature) it turns brownish, when the plankton depletes the nutrients and begins to die. At that height, the more or less rapid decomposition of the dead organisms can lead to the depletion of oxygen in the water and, as a consequence, the massive death of fish and other organisms.