What is Plankton?
General information on plankton
Plankton is the name of a set of very small organisms and microorganisms (floating or sinking) which is at the base of the aquatic food chain (for example tiny fish, manta rays, whale sharks, cetaceans, etc.), plays a primary role in the biogeochemical cycles of many elements (such as oceanic carbon) and produces oxygen (up to 50% of the total on the planet).
Generally of marine bio- and ecological interest, plankton (or rather, a part of it) is also a livelihood resource for some human activities. We are talking about krill and some microalgae.
Let’s go into more detail.
Did you know that…
The name plankton comes from the Greek adjective “planktos”, meaning wanderer (adrift, wanderer, wanderer), and by extension was coined by Victor Hensen in 1887.
The study of plankton is referred to as “planktology” and a planktonic individual is referred to as a “plankter”.
Krill and Algae
Plankton krill
Krill is a group of creatures, more precisely crustaceans, which are part of the plankton – macroplankton (see below). Fished and used above all as feed for fish farms (especially salmon and trout ), it also represents a substrate for the extraction of fats used as food supplements.
Krill oil is rich in omega 3 fatty acids , in particular:
- Eicosapentaenoic acid – EPA
- Docosahexaenoic acid – DHA.
Plankton algae
In plankton there are various types of algae that make up the so-called phytoplankton. Only one, however, has been assessed as suitable for food consumption: the unicellular Tetraselmis chuii . Very rich from a nutritional point of view, it is considered the last frontier of food supplements – functional foods .
This plankton alga contains above all the fatty acids EPA and DHA , vitamin C , vitamin E and vitamin B12 ( cobalamin ). Cultivated in aquaculture, it is processed and marketed in the form of dehydrated powder, sometimes in capsules or tablets.
The distribution companies do not provide particular recommendations on the conservation of the product even if, as we will see in the next paragraph, it could be very useful to follow some precautions.
Omega 3 from plankton
Produced in the body starting from alpha linolenic acid (ALA – typical of foods of vegetable origin such as oilseeds , the germ of starchy seeds , vegetables , fruits, etc.), although they are metabolically more active than their precursor, EPA and DHA are not considered essential.
On the other hand, the metabolic pathway of omega 3 is partially shared by omega 6 which, being more abundant in the diet, tend to limit the availability of enzymes . For this reason it is recommended to divide the dietary intake of omega 3 by taking not only foods rich in ALA, but also foods with EPA and DHA.
Eicosapentaenoic acid and docosahexaenoic acid perform many beneficial functions; the main ones are:
- Cell membrane constituents
- Precursors of anti-inflammatory eicosanoids , which fight metabolic inflammation
- Antiplatelet agents , thin the blood
- They improve the profile of lipaemia, especially by decreasing triglycerides in the blood
- They modulate blood pressure , reducing it if excessive
- They counteract the serious damage of type 2 diabetes mellitus
- At a young age they support eye and brain development
- They preserve brain activity in old age
- They can improve mood by counteracting certain depressive symptoms
- It is hypothesized that they have a positive effect on the sports inflammatory frameworks of injuries to tendons , joints and muscles .
However, it must be specified that EPA and DHA, therefore also krill oil and presumably also planctic algae powder, are rather perishable and must not be exposed to: light, heat, oxygen and free radicals . For greater conservation, antioxidant vitamins are added such as tocopherols ( vitamin E ) and some equivalent retinols ( provitamins A, such as carotenoids , for example beta carotene , astaxanthin , lycopeneetc). Furthermore, the conservation of krill oil should preferably take place in the refrigerator, in airtight and dark containers, for limited periods of time.
We conclude by emphasizing that plankton oil is qualitatively superior to that of fish (for example salmon ) and fish liver (for example cod ). Equaled only by multicellular algae oil (they are not the same as we mentioned above, which instead belong to the unicellular group), it has an excellent level of purity and a very low concentration of pollutants (mercury, lead , dioxins , etc. ) . It is mainly marketed in the form of gelled capsules.
Other Uses
Role of plankton in fish farming
We have said that krill is widely used as fodder for fish farming, but the importance of plankton in this kind of activity is much wider.
Environmental phytoplankton and zooplankton play a long-recognized and proven role in extensive and semi-intensive fish farming . Decades have passed since breeding management strategies have evolved, based on the detection of planctic trophism, demonstrating the enormous importance of this element not only in open waters, but also in artificial environments created by man.
Damaging the marine ecosystem at the base, harming the planktonic population (for example with pollution, the excessive extraction of krill, etc.), means causing irreparable damage which will inexorably also affect human life.
Biology
Biological notes on plankton
Plankton, being unable to swim effectively, move thanks to currents and waves in the so-called pelagic zone of the oceans, seas and inland waters (lakes, rivers, valleys, etc.).
Given the heterogeneity of the creatures that compose it, plankton cannot be considered all the same. It can be differentiated according to occupation in the water column (necton and benthos), locomotion capacity, stage of development (some creatures are plankton only at a young age, such as fish, sea urchins, starfish , etc.), to the biological kingdom it belongs to (zooplankton, phytoplankton, bacteria and unicellular algae) and to the dimensions.
Below we will propose two of the most important classification systems.
Classification of plankton into functional or trophic groups
Plankton are divided into various functional (or trophic) groups. This criterion differentiates the planctic community into broad groups of producers, consumers and recyclers. However, determining the trophic level of plankton is not straightforward. For example, although most dinoflagellates are photosynthetic producers or heterotrophic consumers, many species fulfill both roles. In this mixed trophic strategy (known as mixotrophy) organisms act as both producers and consumers, switching between ato each other in response to environmental conditions. For example, relying on photosynthesis when nutrients and light are plentiful, then switching to predation when growing conditions become adverse. Recognition of the importance of mixotrophy as an ecological strategy is growing, as is the breadth of the role it can play in marine biogeochemistry.
| Phytoplankton : made up of autotrophic prokaryotic or eukaryotic algae that live near the surface of the water in the presence of light for photosynthesis. Among the most important groups are the diatoms, the cyanobacteria , the dinoflagellates and coccolithophores (the prokaryotic phytoplankton is also the bacterioplankton – see below). |
| Zooplankton : made up of small protozoans or metazoans (for example crustaceans and other animals) that feed on other plankton. Also included are eggs and larvae of larger nektonic animals such as fish, crustaceans and annelids. |
| Bacterioplankton : made up of bacteria and archaea that play an important role in the remineralization of organic material in the water column (prokaryotic phytoplankton is also bacterioplankton). |
| Mycoplankton : made up of fungi and fungiform organisms which, like bacterioplankton, are useful for remineralization and in the metabolism of nutrients. |
Division of plankton by size
Plankton also divide based on size.
| Group | Cut | Example |
| Megaplankton | > 20cm | Jellyfish, cephalopod molluscs, Amphipoda etc |
| Macroplankton | 2-20cm | Jellyfish, cephalopod molluscs, doliolids and pyrosomes, krill (Euphausiacea) etc. |
| Mesoplankton | 0.2-20mm | Jellyfish, metazoans, cladocera etc |
| Microplankton | 20-200 µm | Large eukaryote protists, phytoplankton etc |
| Nanoplankton | 2-20 µm | Small eukaryotic protists, diatoms, etc |
| Picoplankton | 0.2-2 µm | Small eukaryotic protists, bacteria etc |
| Femtoplankton | < 0.2 µm | Marine viruses |
