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6 Algae
The physiological needs of algae
Ezhommoù fiziologel ar bezhin
How do algae feed themselves?
All algae contain chlorophyll, just like land plants. To feed themselves they use photosynthesis, and for that they need:
- light — indeed, no seaweed grows where there is too little light to supply the energy photosynthesis requires;
- water — which is everywhere… except at low tide;
- CO₂ — present in dissolved form in seawater;
- mineral salts — also present in seawater.
Algae also feed by osmosis: through their semi-permeable membrane, their thalli absorb the nutrients found in seawater — nitrogen and phosphorus in large quantities, along with trace elements.
What is photosynthesis?
Using light energy and the pigments they contain, algae carry out photosynthesis. They capture the carbon dioxide exchanged in dissolved form between the atmosphere and the ocean. This allows them to produce the sugars they need for food, and to release oxygen.