What is zooplankton
Introduction to zooplankton
Zooplankton is a type of plankton (a set of aquatic organisms) that is heterotrophic (that is, it is not able to synthesize its own nourishment) that feeds on bacterioplankton, phytoplankton, other zooplankton, nektonic organisms and decomposition residues (detritivorous attitude) .
The word "zooplankton" comes from the Greek "zoon", which means "animal", and "planktos", which means "wandering". Like all plankton, zooplankton also moves continuously in the oceans, seas and internal freshwater courses.
The organisms that structure zooplankton are generally microscopic and only a few - such as jellyfish - have larger dimensions and are visible to the naked eye.
Some elements of zooplankton are fished by humans and used for various purposes. For example, krill (very small crustaceans) is used in aquaculture as a forage for the breeding of some fish. Furthermore, from the krill it is possible to extract an edible oil, generally used as a supplement, very rich in omega 3 (EPA and DHA) and fat-soluble vitamins.
The presence of zooplankton in the seas and in watercourses is fundamental. It is at the base of the food chain as the prey of many creatures and, having an attitude that is also detritivorous, participates in a multipurpose way to support the balance of the ecosystem. However, in some areas of the planet, the increasing level of pollution and professional fishing (of krill) are compromising the density of zooplankton with repercussions, to say the least, of concern.
Nutritional Properties
Nutritional properties of zooplankton
When we talk about the nutritional properties of zooplankton, we mean more precisely the chemical characteristics of krill. Krill is a portion of the zooplankton consisting of animals of the Subphylum Crustacea, Class Malacostraca, Superorder Eucharida and Order Euphausiacea. The numerous families and the various kinds of krill colonize, even if sometimes in a sectorial way, all the oceans and the Mediterranean Sea.
Zooplankton is a nutritional source of high biological value proteins, omega 3 fatty acids and vitamin A; these characteristics would make it a worthy exponent of the first fundamental food group. However, since it is not used for specific gastronomic applications, zooplankton can not be considered a real food. From the zooplankton on the other hand valuable oily derivatives are obtained, rich in polyunsaturated fatty acids docosahexaenoic and eicosapentaenoic, and of vitamin A; they are mainly used as supplements. Furthermore, zooplankton krill is also a food widely used for feeding domestic and farmed fish.
In 2011, the US Food and Drug Administration (FDA) published a non-objection letter to the recognition of krill oil as a safe product for human consumption (GRAS).
Did you know that ...
The most dense area of krill is the Antarctic, in which it is estimated that around 400 million tons of small crustaceans can stand. Fishing is however on the rise, with a + 39% between 2010-2014. The countries that collect the most are: Norway, Korea and China.
Zooplankton: eicosapentaenoic acid and docosahexaenoic acid
Produced in the body starting from alpha linolenic acid (ALA - typical of plant-based foods such as oilseeds, starchy seed germs, vegetables, fruits, etc.), although they are metabolically more active than their precursor, acid eicosapentaenoico and docosahexaenoic (EPA and DHA) are not considered essential.
On the other hand, the metabolic pathway of omega 3 is partially shared by the omega 6 which, being more abundant in the diet, tend to limit the availability of enzymes. For this reason it is advisable to fractionate the food intake of omega 3 by taking not only foods rich in ALA, but also foods with EPA and DHA. When the diet is not sufficiently rich in eicosapentaenoic and docosahexaenoic acid, it may be very useful to use a food supplement such as krill oil, algae oil, phytoplankton powder etc.
EPA and DHA perform many beneficial functions; the main ones are:
- Constituent of cellular membrane
- Precursor of anti-inflammatory eicosanoids, which fight metabolic inflammation
- Anti-caking, blood thinning
- They improve the profile of lipemia, especially by decreasing the triglycerides in the blood
- They modulate blood pressure, reducing it if excessive
- Counteract the severe damage of type 2 diabetes mellitus
- At an early age they support eye and brain development
- Preserve brain activity in old age
- They can improve mood by counteracting certain depressive symptoms
- It is hypothesized that tendons, joints and muscles are positively affected by sports inflammatory patterns.
It is nevertheless necessary to specify that EPA and DHA are perishable nutrients and must not be exposed to: light, heat, oxygen and free radicals. For greater preservation, antioxidant vitamins such as tocopherols (vitamin E) and some retinol equivalents (provitamins A, such as carotenoids, such as beta carotene, astaxanthin, lycopene, etc.) are added . Furthermore, the preservation of omega-3 rich oils should preferably be in the refrigerator, in airtight and dark containers, for limited periods of time.
We conclude by pointing out that the zooplankton oil is qualitatively superior to that of fish (for example salmon) and fish liver (for example cod). Equaled only by algae oil (which is not part of phytoplankton and are instead multicellular), it has an excellent degree of purity and a very low concentration of pollutants (mercury, lead, dioxins, etc.). It is sold mainly in the form of gel capsules.
Zooplankton flavor
Zooplankton has a salty taste and a more intense fish flavor than the usual shrimp. The non-digestible exoskeleton based on chitin must be removed before processing.
Ecology
What is zooplankton made from?
Zooplankton is a category that encompasses a wide range of organisms, with varying sizes, including small protozoa and large metazoans.
It encloses oloplanctonic organisms whose entire life cycle develops inside the plankton, but also meroplanctonic organisms that spend part of their life in plankton before going on to benthic existence.
Although zooplankton is mainly carried by water currents, many organisms are provided with autonomous locomotion, used mainly to avoid predators or to hunt.
Main zooplankton groups
The most important ecologically important groups of protozoan zooplankton are the foraminifera, the radiolarians and the dinoflagellates (some mixotropics).
Among the metazoans, instead, we mention:
- Cnidarians, like jellyfish
- Crustaceans, such as copepods, ostracods, isopods, amphipods, mysids and krill
- Dying (worms)
- Mollusks, like the pteropods
- Cordati, as salpid and juvenile.
Food habits and attitudes of zooplankton
This vast phylogenetic range involves a certain variability in feeding behavior; systems such as filtration, predation and symbiosis with autotrophic phytoplankton (microalgae) coexist.
Zooplankton feeds on: bacterioplankton, phytoplankton, other zooplankton (also cannibalism), debris and even nektonic organisms. Consequently, zooplankton is found mainly, but not only, in surface waters where resources (phytoplankton or other zooplankton) abound.
Displacements and migrations of the zooplankton
Despite moving into vast oceans, zooplankton can simply colonize even a single geographical area. The countless species of zooplankton are not distributed randomly, let alone uniformly, but in patches.
Although above the mesopelagic there are few "physical barriers" to prevent the migration of zooplankton, some species are strictly bound to the parameters of salinity and temperature; others, on the other hand, can withstand much more variable gradients.
The distribution of zooplankton can also be influenced by biological factors, as well as by other physical factors. Biological factors include reproduction, predation, phytoplankton concentration and vertical migration (on the water column). The physical factor that most affects the distribution of zooplankton is the mixing of the water column that influences the availability of nutrients and, in turn, the production of phytoplankton.
The biological role of zooplankton
Zooplankton plays a decisive role in maintaining the aquatic food chain. This is because, through the consumption and processing of phytoplankton, bacterioplankton and organic material, zooplankton grows and takes on the role of a food resource for the highest trophic level organisms (including fish and some cetaceans). Being small in size, as the phytoplankton grows (for example during spring flowering), zooplankton responds by increasing rapidly.
Zooplankton and cholera
Zooplankton can also act as an incubator of certain infectious diseases. It has been discovered, for example, that the zooplankton crustaceans host - or rather carry - the bacterium Vibrio cholerae (cause of cholera). This happens because the vibrios are able to adhere to the chitinous exoskeleton, obtaining carbon and nitrogen, thus improving their survival capacity.
