How are toxic microalgae monitored?

Phytoplankton is a plant made up of unicellular microscopic algae (microorganisms) that grow in seawater or estuarine water.

In particular, it produces half of the oxygen we breathe and “receptors” CO through the process of photosynthesis. It is the first primary producer in the marine environment, which puts it at the beginning of the seafood chain.

To date, more than 5,000 species have been identified worldwide, some of which (about 200 species) may be harmful or poisonous during an event called “Blooms” (or). Blooming)

When conditions are favorable, plankton expands in a very important way, thus causing the formation of colored water (red, green, brown), foam at sea and on the coast, and even the production of toxins accumulated in the food chain. Became dangerous for humans.

These flowers thus degrade marine ecosystems, alter their quality and pose a risk to human health.

Phytoplankton requires careful monitoring for many reasons.

Phytoplankton and its response to environmental change

Phytoplankton respond very quickly to changes in their environment and play an important role in coastal ecosystems. This makes it an excellent indicator of environmental change and so it is often used as an indicator to contribute to the assessment of the quality of marine ecosystems.

Algal flowers can indicate imbalance in their environment. Here, a flower Mesodinium rubrum Color the waters of the Mediterranean.
Pierre Garnez / ISOmer / Nantes University, Contributed by the author

Several studies have thus focused on the analysis of the main features of phytoplankton, from the point of view of overall abundance, the ratio of the main taxonomic groups (examples of dinoflagellate / diatom ratios, often relating to the possible toxic part of phytoplankton, phytoplankton). Its dynamics between time and space (beginning, end, and amplitude of blossoming).

These changes in phytoplankton biomass, abundance, and motility are often related to environmental factors: temperature, salinity, light, and nutrient availability (nitrogen, phosphorus, and silica).

Natural or ethnographic sources make it possible to better identify these changes by understanding phytoplankton’s response to changes in environmental conditions.

For example, phytoplankton analysis provides information on vulnerabilities in coastal regions. When the nutrient supply (especially nitrogen, phosphorus) is excessive and the conditions are optimal (light, water clarity, currents), the development of phytoplankton will be favorable to a point where it will cause defects in the frozen ecosystem. This coincides with the eutrophication process.

The depletion of nutrient input from reservoirs to the sea will thus encourage the depletion of flowers of certain species, which in general will lead to depletion of the total organic matter of phytoplankton, as recently shown in the English Channel and the North Sea.

However, the response of phytoplankton to this improvement in environmental quality may not be direct, and it may take years or even decades to see the effects on the environment. Moreover, it is the balance between different nutrients (nitrogen to phosphorus ratio) that can be critical in limiting the spread of a given microorganism.

The study of phytoplankton dynamics involves observing the date and end of algae flowers as well as their amplitude and duration.

Thus, for some dinoflagellates, flowers have been seen earlier in the North Sea.

One of the most important possible consequences on ecosystem function is the development of phytoplankton and the time interval between its consumers, which limits the exchange of food between the various links in the food chain.

This can lead to major changes in the phytoplankton (animal plankton, fish, shellfish) species fed directly or indirectly. This can lead to a limitation of marine resources, an essential source of protein for human nutrition.

A better understanding of the relationship between phytoplankton and its environment based on old and new data makes it possible to better understand the functionality of this complex biological component. This will then make it possible to interpret and predict new phenomena, such as the distribution of species in response to the evolution of biodiversity and climate change.

Phytoplankton, a health hazard

In phytoplankton, some species produce toxins. This is especially true of sex Dynophysis (Producers of diarrhea toxins), Pseudo-nitzschia (Producers of amniotic toxins) and Alexandrium (Producers of paralytic toxins)

Bivalve mollusks filter a few liters of water per hour and feed the phytoplankton. When it comes to poison-producing species, they accumulate in the shellfish, which, in turn, puts the human consumer at risk of contamination.

Other tropical species of the genus Gambiardiskas (Producer of siguetoxin), origin of siguetra, a food poisoning present in the Pacific Ocean, Indian Ocean and West Indies, among others …

Read more: In the Caribbean, microalgae that cause food poisoning

Outside of the poison-producing species, other species are found to be harmful to the ecosystem.

Thus, during strong flowering, phytoplankton eventually dies. Its degradation then consumes large amounts of oxygen, which harms other living creatures in the vicinity, especially among the Benthic species who cannot “escape” from the area and die of suffocation. In this case, for example, in the case of shellfish raised for human consumption.

Some species, when they bloom, produce mucus, which makes seawater more “dense” and viscous, trapping fish gills (which leads to their death), or may cause swelling. Accumulated at beaches or ports, affected use (e.g. Fiocystis globosa In the English Channel and the North Sea.

Observe phytoplankton

For all these reasons, it is necessary to have a view of the evolution of phytoplankton in space and time. For this, the EFRMER rely on REPHY, an observation and observation network.

Dynophysis acuta Under a scanning electron microscope.
Veronica Sechet / Ifremer / Phytox / Fisalog and Nicholas Chomerat / Ifremer / LERBO, Contributed by the author

It involves taking sea water from a defined frequency, usually monthly to weekly, from a defined location. Depending on the location, the sample is taken from the boat or from the pontoon or dyke.

These seawater samples are analyzed (manually) under a microscope to detect and count phytoplankton.

When poisonous-producing species are present above the warning threshold, shellfish sampling begins in nearby absorbed areas. If the concentration of toxins in the shellfish is above the regulatory threshold, the affected areas may be closed by state services to protect the shellfish consumers.

Contribute to new technology

Recent electronic and computer advances have made it possible to observe phytoplankton with less conventional methods, automating samples and increasing the number of analyzes and / or measurements in time and space.

Thus, it is now possible to study phytoplankton with:

  • Image Analysis System: An Algorithm Allows Automatic Recognition Of Phytoplankton Cells Passed In Front Of The Camera Lens

  • Genetic Studies: We’re talking about metabarcoding, metatranscriptmics, and metagenomics techniques.

  • Sensors installed on boats or boats: We can measure the biomass of phytoplankton directly in the environment, and it is even possible to divide these global organisms into different phytoplankton groups according to their photosynthetic pigment structure.

  • Modeling: The creation of a digital marine ecosystem makes it possible to examine evolutionary conditions by changing the parameters of the model according to past, present or future changes in the environment.

  • Products obtained from water color observation: This involves observing phytoplankton using satellite images.

S-3 EUROHAB project

This last point can be illustrated by the S-3 EUROHAB project, which uses data from the European Corponicus Sentinel 3 satellite to track harmful and toxic algal blooms on the English Channel.

Satellite image centered on the steps, the blooms are shown in blue-green
The risk of blooming from satellite images of April 24, 2020 is high Fiocystis In the Eastern Channel.
S3-Eurohab, Contributed by the author

Satellite data has been used to create an online warning system, the first of its kind in Europe, to warn marine managers and the fishing industry about potentially harmful algae blooms.

Alerts are freely accessible through the EUROHAB portal.

Finally, outside of the risk of algal bloom, the online alert tool provides indicators of water quality or physical or climatic properties (turbidity, surface temperature, etc.) that can help professionals and users manage their activities and improve their practices.

The challenge for scientists now is to combine all this knowledge to better observe, better understand and therefore better predict evolution and therefore better manage this phytoplankton compartment essential for life on Earth.

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