Tuesday, June 18, 2024

Magical but poisonous, this is microalgae from the ocean

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Maria Gill
Maria Gill
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The Images of Science format allows you to decode an image of particular interest from a scientific point of view, describe it and understand its challenges.

Since mid-March 2021, the blue waves have stunned California residents Laguna Beach. Although this phenomenon peaked annually in the spring of 2020. Then the Pacific Ocean was streaked with scarlet red during the day, giving way to brilliant waves of bright blue light. By night, Under amazed eyes Observers.

The phenomenon of red tides during the day and incandescent at night is the result of the massive proliferation of red micro-algae. Lingolodinium polydraIt is observed in southern Africa, northwest Spain, on the coasts of Mexico and California. Some of these red tides are real environmental and economic disasters because they cause the death of many marine organisms (fish, molluscs, mammals or birds).

In all regions of the world where these phenomena are present, we are currently witnessing an increase in the frequency and intensity of red tides and red tides. Toxic microalgae Generally. Increases in water temperature and human releases of nitrogen and phosphorous are suspected to be the main causes of these changes.


Not all red tides are energetic. For some types of illuminating microalgae, it is a mechanical stimulus, such as the movement of waves colliding on the shore or the passage of a boat, that triggers the bioluminescence. The light emitted from this microalgae follows a daily rhythm, with strong intensity that can be observed at night and light Not present or neglected during the day. The duration and intensity of the blink varies between species, and may be related to cell size (larger cells emit more light). for example, Polydra L. It transmits an average of 130 to 150 ms but Pyrocystis fusiformis Can emit flashes lasting up to 500ms. The intensity of the flashes is 10 times8 Up to 109 Photons per second, a relatively faint glow to the human eye.

The environmental role of bioluminescence is still poorly understood, but some types of dynamic flagellates use this light as a “theft alarm”. When a predator eats dinoflagellates, the light emission is visible from a distance and attracts a secondary predator (fish for example) that will attack the first predator of the whip, thus saving it from predation. However, this has been brought up recently Polydra L. It emits weaker light than other species and will be less effective at attracting visible predators.

A double cause of poisoning

The mechanism underlying their toxicity depends on the dynamic flagellate species: in some cases, a high abundance of microalgae leads to a lack of harmful oxygen to other organisms, while others create powerful toxins.

Polydra L. It is known to make isotoxins toxins, but in trace amounts. Yet the red tide Polydra L. it causes Many marine creatures die: crabs, bivalves, octopuses, fish and dolphins. These deaths are hardly attributed to isotoxins because this toxin is not very potent and was poorly concentrated in the water – as we showed in a study currently being validated by their peers. On the other hand, it is the concentration of dissolved oxygen in the water and the pH of the water They both fell off During this period, the egg-smelling foul odor emanating from this red bloom, which was perceived several kilometers from the coast, lasted for a week, indicating an intense production of sulfur gases by the bacteria. At present, we are studying methods of hypoxia in the environment and the production of sulfide gases, as possible causes of the observed deaths.

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In humans, yessotoxin can be responsible for various symptoms – itching, sore eyes, sore throat, and nausea. In fact, for the first time, it was detected in aerosols on La Jolla Beach during this red tide. Because our respiratory system is incredibly sensitive, it is not likely that detected levels of yessotoxin were the cause of the reported human pain. The cracking of toxins produced by other toxic flagellates has also been observed in Florida with Karenia Braves (Patents) and in the Mediterranean with Austriopsis See Ovata (Ovatoxin).

A little bit One of the algae species is toxic and bioluminescent. Common ability Polydra L. It emits bioluminescence and toxins It can be related To the mechanism of aposematism, a visual warning of the danger of attacking it.

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