Algae? What is that?

We take off - and it is also my first time in an aeroplane! Anne-Gaëlle asks me if I am ready with my questions for the Algonauts. I do have some - like, for example, what is an algae?

Well… guess what: the word algae is not even a scientific term! Rather a “descriptive convenience”… As I understand it, this word is handy to group together in the same bag organisms which are actually very different.

Yet, looking at them from the beach, seaweeds all seem the same, don’t you think so? Apparently not! A green alga and a tree could be closer cousins than two species of algae1.

So, what are their common points?

Algae are aquatic plants. They perform photosynthesis. If there is light, carbon dioxide, nutrients and water, even transiently, they can grow and they can be observed in almost all environmental conditions of the planet.

But not all aquatic plants are algae!

The algal diversity is characterized by their differences in:

  • Size : from a few micrometers to several tens of meters, there are two main groups: microalgae, invisible to the naked eye, also part of a group called plankton2 and seaweeds / macroalgae, that we can observe at the beach.
  • Reproduction mode: asexual reproduction, sexual reproduction performed in one, two or three steps… Gosh, I would have never suspected that algae could be so creative in their sexuality!
  • Habitat: freshwater, marine, brackish waters, terrestrial habitat, bear furs3, etc! Some of them even live in symbiosis with other organisms as it is the case for corals, giant clams or lichens4.
  • Color: green, red, brown, golden, blue…

Pardon?! From this point, I stopped listening to Anne-Gaëlle who was telling nonsense. Blue-green algae?! Be careful, here comes Gargamel! Whatever! Nonetheless, I wonder what determines the color of algae5…

Anne-Gaëlle sulked till London. When we arrived at Heathrow airport, I told her I believed in her stories about smurf algae, but it was mostly because I did not want her to leave me alone for getting the connecting flight. I wonder if I still have a way-out to cross the Channel and go back to Brittany…

Learn more

  1. The study of these “cousin relationship” between living organisms is called phylogeny. ↩

  2. The word plankton refers to all the living organims, plants and animals, suspended in the water mass, moving with the currents, which for the majority of them are invisible to the naked eye. Learn more about the plankton through the Plankton chronicles ↩

  3. Yes, really! Green polar bears exist! This phenomenon has been observed in zoos. When humidity and temperature conditions are favorable for their growth, microscopic algae develop in the fur of mammals and lead to that color change! ↩

  4. A symbiosis is a mandatory association between two species (symbiont organisms), which can not live without the other one. For example, a coral is a combination of an animal organism, the polyp, with an unicellular alga, a zooxanthella. The polyp provides a shelter, some stable environmental conditions, CO2 and nutrients (such as its nitrogen and phosphate waste) to the zooxanthella. In exchange, the zooxanthella provides oxygen and additional food (organic matter produced by photosynthesis) to the polyp. In the case of the lichen, the association is a combination of a fungus and an alga. ↩

  5. Don’t worry Jacqueline! We will have the opportunity to talk again about pigments, chloroplasts or carotenoids! ↩