What is phytoplankton? Most phytoplankton are too small to be seen with the naked eye. However, in fairly high quantities, some species may be visible as colored spots on the surface of the water, due to the content of chlorophyll inside their cells and auxiliary pigments such as phycobiliproteins or xanthophylls.
What is phytoplankton
Phytoplankton is a photosynthetic microscopic biotic organism that lives in the upper water layer of almost all the oceans and lakes on Earth. They are the creators of organic compounds of carbon dioxide dissolved in water - that is, the initiators of the process that supports the aquatic food web.
Photosynthesis
Phytoplankton receives energy through photosynthesis and therefore must live in a well-lit surface layer (called the euphotic zone) of the ocean, sea, lake or other body of water. Phytoplankton accounts for about half of all photosynthetic activity on Earth. Its cumulative energy fixation in carbon compounds (primary production) is the basis for the vast majority of oceanic and many freshwater food chains (a notable exception is chemosynthesis).
Unique views
Although almost all phytoplankton species are exceptional photoautotrophs, there are some of them - mitotrophs. Usually these are unpigmented species that are actually heterotrophic (the latter are often considered as zooplankton). Dinoflagellar genera, such as Noctiluca and Dinophysis, which produce organic carbon by ingesting other organisms or detrital material, are best known.
Value
Phytoplankton absorbs the energy of the sun and nutrients from water to produce its own food. During photosynthesis, molecular oxygen (O2) is released into the water. It is estimated that around 50% or 85% of the world's oxygen is produced during phytoplankton photosynthesis. The rest is produced by photosynthesis by land plants. To understand what phytoplankton is, it is necessary to realize its great importance for nature.
Mineral Bond
Phytoplankton is critically dependent on minerals. First of all, these are macroelements, such as nitrate, phosphate or silicic acid, the availability of which is determined by the balance between the so-called biological pump and the rise of deep, nutrient-rich waters. However, in large areas of the World Ocean, such as the Southern Ocean, phytoplankton is also limited by the absence of micronutrient iron. This has led some scientists to advocate fertilization of iron as a means of counteracting the accumulation of carbon dioxide (CO2) produced by humans in the atmosphere.
Scientists have experimented with adding iron to water (usually in the form of salts such as iron sulfate) to promote the growth of phytoplankton and bring atmospheric CO2 to the ocean. However, disputes about ecosystem management and the effectiveness of fertilizer application in iron slowed down such experiments.
Diversity
The term phytoplankton encompasses all photoautotrophic microorganisms in aquatic food chains. However, unlike terrestrial communities, where most autotrophs are plants, phytoplankton is a diverse group including the simplest eukaryotes, such as eubacterial and archaebacterial prokaryotes. There are about 5,000 known species of marine phytoplankton. How this diversity has developed, despite limited food resources, is still unclear.
The most important phytoplankton groups include diatoms, cyanobacteria and dinoflagellates, although many other algae groups are also represented in this extremely diverse group. One group, coccolithophorids, is (partially) responsible for releasing significant amounts of dimethyl sulfide (DMS) into the atmosphere. DMS oxidizes to form sulfate, which in areas with a low concentration of aerosol particles can contribute to the formation of special areas of air condensation, which mainly leads to an increase in cloudiness and fog above water. This property is also characteristic of phytoplankton of lakes.
All types of phytoplankton support different trophic (i.e., food) levels in different ecosystems. In oligotrophic oceanic areas such as the Sargasso Sea or the South Pacific Ocean, small-sized unicellular organisms, called picoplankton and nanoplankton (also called picoflagellates and nanoflagellates), are most often found among phytoplankton. Basically, phytoplankton is understood to mean cyanobacteria (Prochlorococcus, Synechococcus) and pico-eukaryotes, such as Micromonas. In more productive ecosystems, large dinoflagellates are the basis of phytoplankton biomass.
Effect on the chemical composition of water
At the beginning of the twentieth century, Alfred C. Redfield found a similarity in the elemental composition of phytoplankton with the main dissolved nutrients in the deep ocean. Redfield suggested that the ratio of carbon to nitrogen to phosphorus (106: 16: 1) in the ocean is controlled by the needs of phytoplankton, since phytoplankton subsequently releases nitrogen and phosphorus as they remineralize. This so-called “Redfield ratio” in describing the stoichiometry of phytoplankton and sea water has become a fundamental principle for understanding the evolution of marine ecology, biogeochemistry, and also what phytoplankton is. However, the Redfield coefficient is not a universal value and may diverge due to changes in the composition of exogenous nutrients and microbes in the ocean. The production of phytoplankton, as it should already be, the reader realized, affects not only the level of oxygen, but also the chemical composition of ocean water.
Biological features
The dynamic stoichiometry inherent in unicellular algae reflects their ability to store nutrients in the internal reservoir and alter the composition of the osmolyte. Different cellular components have their own unique stoichiometric characteristics, for example, resource (light or nutrient) data collection devices, such as proteins and chlorophyll, contain a high concentration of nitrogen, but with a low phosphorus content. Meanwhile, genetic growth mechanisms, such as ribosomal RNA, contain high concentrations of nitrogen and phosphorus (N and P, respectively). The food chain phytoplankton-zooplankton, despite the difference between these two types of creatures, is the basis of the ecology of water spaces throughout the planet.
Life cycles
Based on the distribution of resources, phytoplankton is divided into three stages of life: survival, flowering and consolidation. The surviving phytoplankton has a high N: P ratio (nitrogen and phosphorus) (> 30) and contains many resource collection mechanisms to support growth with scarce resources. Flowering phytoplankton has a low N: P ratio (<10) and is adapted to exponential growth. Consolidated phytoplankton has a similar N: P to Redfield coefficient and contains a relatively equal ratio of growth mechanisms and resource accumulation.
Present and future
A study published in Nature in 2010 showed that marine phytoplankton has declined significantly in the oceans over the past century. It is estimated that phytoplankton concentrations in surface waters have decreased by about 40% since 1950 at a rate of about 1% per year, possibly in response to ocean warming. The study sparked controversy among scientists and led to heated debate. In a subsequent study in 2014, the authors used a large measurement database and revised their analysis methods to take into account several published criticisms, but in the end came to similarly disturbing conclusions: the number of phytoplankton algae is rapidly declining.