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2 Algae
Classification by size: microalgae and macroalgae
Ur rummatadur dre vent : mikrobezhinoù ha makrobezhinoù
Algae can be divided into two quite distinct groups:
- Microalgae are microscopic and often made up of a single cell. We only sense their presence when they multiply in great numbers and turn the water green or brown.
- Macroalgae are visible to the naked eye, as they are made of many cells held together within a membrane. These are the ones we can see on the rocks.
Their shapes and sizes vary greatly from one species to another.
Diatoms, microalgae found everywhere
Diatoms are single-celled microalgae present in every aquatic environment, with a preference for cold waters. They are enclosed in an external silica skeleton called a frustule.
They are found as deep as the mesopelagic zone, the twilight layer lying between 200 and 400 metres down, between the sunlit surface and total darkness. Hard to reach — it often takes hours of sailing to get there — it remains little known. In Europe, Villefranche-sur-Mer is the only place where a depth of 200 metres can be reached within a quarter of an hour from the shore.