Marine plankton are not only present in all the oceans, but it is also the basis of the food web of living marine organisms.

When we breed a piece of reef in a closed environment (recifal aquarium), it is interesting to understand how plankton works. Especially if we want to get closer to a maintenance similar to the natural environment.

The origin of the term plankton comes from the Greek "Plankton" resulting in " wander ", He points to theall plants (Phytoplankton) and animals (Zooplankton) that are microscopic or small in size and cannot move against the current.

This article aims to popularize the origin andphytoplankton environment to reproduce it in a closed environment.

Marine phytoplankton are the basis of the aquatic food chain

Phytoplankton refers to the set of structured microscopic algae of unicellular algae.

As with terrestrial plants, phytoplankton or “Plant plankton” makes its substance from carbon dioxide (CO2) and mineral salts contained in seawater, phosphates, potassium, nitrogen, silica ...

These algae are the basis of the diet of certain animals such as filter-feeding bivalves, jellyfish, but also zooplankton including microfauna.

In the oceans we find the phytoplankton mainly on the surface where it uses photosynthesis to develop. This photosynthesis is made possible by the chlorophyll contained in phytoplankton cells.

For a long time, it was rarely mentioned the benefits of phytoplankton in a reef aquarium. However, in recent years, many recifalists have been trying to maintain maintenance close to the natural environment. Note that in the natural environment, many common reef aquarium animals are filter feeders.

These include: gorgonians, flaming scallops, sponges, giant clams and other filtering bivalves, soft corals, LPS corals, etc.

When the aquarist cleans the windows of his reef aquarium, windows on which a thin film of phytoplankton is thus formed, this addition happens naturally without him realizing it, but very often not enough at the risk of malnutrition or even starving them.

The different species of marine phytoplankton

More generally, phytoplankton is made up of thousands of species that are divided into several groups:

• Chrysophyceae and Chlorophyceae (These are often the phytoplankton that we find in culture: Dunaliella Salina – Nannochloropsis Oculata – Nannochloropsis Salina – Tetraslemis Suecica  etc ..)
• Blue algae or cyanobacteria (Natural means to fight against with the addition of marine phytoplankton Synechococcus SP )
• Diatoms,
• Coccoliths,
• Dinoflagellates.

Chrysophyceae and Chlorophyceae

- Chrysophyceae (T-Isochrysis) are yellow to brown unicellular algae, elongated in shape and small in size (2 to 3 microns). Thanks to their two flagella, chrysophyceae can move around without, however, countering currents.

They are particularly interesting for their nutritional qualities. In the natural environment, they are used as food for marine organisms in their larval stage, such as bivalves (mussels, oysters, shellfish), but also for zooplankton.

- Chlorophyceae are green microalgae living isolated or organized in colonies in marine and fresh waters of temperate and warm zones. Unicellular or multicellular, ovoid in shape, they measure from 1 to 10 microns and can, like chrysophyceae, have two flagella which allow them to remain on the surface.

Chlorophyceae are generally green algae, chlorophyll being very abundant. However, some species have some variants going as far as red such as the phytoplankton dunaliella salina in some cases.

Blue algae or cyanobacteria

Cyanobacteria (or cyanophyceae), or formerly called blue algae, are photosynthetic bacteria. They take advantage of solar energy to synthesize their organic molecules. In a reef aquarium they will capture this light to develop.

The colors of cyanobacteria are due to their different pigments: phycocyanins (blue-green in color), chlorophyll (green) or red (phycoerythrins)

In reef aquarium as in nature, cyanobacteria are always present and can become dangerous if they proliferate. Outraged suffocate living stones and corals, they can release cyanotoxins, which are sometimes fatal to animals.

There are natural ways to fight the proliferation of cyanobacteria, such as competing for food with the addition of bacteria. More generally, good management of the aquarium parameters will also limit its proliferation (management of light, water quality, mixing, nutrients by limiting water changes ..)

However, be careful with “miracle” products which eliminate cyanobacteria in a few days, often chemicals which will not only destroy the cyanobacteria but all the diversity of your microfauna with serious repercussions on your reef aquarium.

A natural way: add algae to fight against algae

Algae which are a scourge like cyanobacteria are mainly benthic forms (i.e. those which attach themselves to sand, living rocks, corals, etc.) while beneficial algae are often planktonic forms (i.e. that is, those that live freely in the water column).

When planktonic algae are sufficiently abundant, they can get checked or even totally root out undesirable benthic algae by competing aggressively with them. Thus benthic algae such as cyanobacteria will no longer have nutrients to develop.

the marine phytoplankton  Synechococcus SP is part of the Cyanophyceae family and is also planktonic. It is the ideal ally for competing with cyanobacteria while allowing the microfauna in your aquarium to develop and nourish your living.

Diatoms

Diatoms or Bacillariophyceae are unicellular microscopic algae of about 2 μm To 1 mm distinct by a siliceous envelope external called the frustule.

- The pelagic forms (which live in the aquarium water column) belong to phytoplankton. These diatoms are photosynthetic, meaning that they need light to develop (unlike the diatoms belonging to the microphytobenthos.)

- The benthic forms (at the bottom of the aquarium) belong to the microphytobenthos, that is, organisms that live at the bottom of the ocean.

Note: Most of the time, diatoms in reef tanks appear on the sand, and can be mistaken for cyanobacteria. The origin is often related to reverse osmosis water added to compensate for evaporation from the recifal aquarium and / or the water used for water changes containing excess silicates. The problem will be quickly resolved with the use of an anti-silicate resin at the outlet of your osmosis unit.

Coccoliths

Coccoliths (from the Greek κοκκος " seed ", Λίθος" rock ") Are the calcium carbonate plates one to ten micrometers in diameter in the shape of a seed that protect the coccolithophorids.

Coccolithophorids are pelagic phytoplankton that we find at the bottom of the oceans and that we know more “vulgarly” in the composition of the chalk (created through the accumulation of their fossilized skeleton)

Dinoflagellates

Dinoflagellates are unicellular microalgae of red-orange color and medium or small in size, between 3 and 50 microns.

Their of them flagella allow to perform relative whirling movements (from the Greek "dino": spinning top) and vertical migrations. Like all microalgae, they reproduce by cell division : a mother cell gives two daughter cells every 12 to 36 hours.

Dinoflagellates occupy an important place (after diatoms) in the staple diet of the marine food chain that extends to large fish and large marine mammals.

These algae are often responsible for green or red tides, contamination of oysters and mussels making them unfit for consumption.

Note: Dinoflagellates are very difficult to eliminate in a reef aquarium (populated with corals), and for good reason, because the zooxanthellae in our corals are also dinoflagelleas! Fortunately there are different shapes, carpet shapes (the hardest to remove) and planktonic shapes (often easily killed by a UV lamp) 

Marine phytoplankton for use in a reef aquarium

Many common reef aquarium animals are filter feeders.

In the natural environment, they often eat a lot of it, and therefore as in the natural environment, the addition of phytoplankton will feed them but also promote the development of microfauna, a fundamental basis for the balance of the ecosystem established. in our micro-reefs.

Depending on the coral and microfauna population, we recommend a regular addition of live phytoplankton. The addition should preferably be carried out in the evening for better assimilation by the corals, whether they are soft, LPS or SPS or the sabelles whose lifespan will depend on planktonic food.

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