Most people think that the air we breathe comes from plants on land, but actually at least half of it comes from seaweed. Just like land plants, seaweeds convert sunlight, carbon dioxide and water into oxygen and energy through a process called photosynthesis. The process is basically the same on land and in the ocean, except seaweeds have slightly different strategies for capturing sunlight. Land plants absorb sunlight through photosynthetic pigments called “chlorophyll”. But different kinds of seaweeds have different pigment cells optimized for absorbing different wavelengths of light. This is because as sunlight hits the water and goes deeper, red light gets absorbed while blue and green wavelengths reach deeper (this is why the oceans look blue and green!).

Seaweeds have adapted different ways to take advantage of these different wavelengths of light. Different types of species (e.g., green algae, brown algae and red algae) contain different pigments that are responsible for creating their different colors. Like land plants, green algae primarily use chlorophyll pigments. Chlorophyll absorb mostly shorter, red wavelengths of light that have a tough time penetrating deeper waters. Brown algae have some chlorophyll, but the main photosynthetic pigment they use is called “fucoxanthin” and it reflects yellow light. Red algae have chlorophyll as well, but they also use bluish “phycocyanin” and reddish “phycoerythrin”. These pigments absorb longer, bluish wavelengths of light. These different types of seaweeds live at different depths so that they can optimize how much sunlight they absorb at the wavelength they’re adapted to use. Once seaweeds absorb sunlight through these pigments, they undergo photosynthesis. A byproduct of this reaction is oxygen, which is released into the atmosphere for us to breathe!

Seaweed gives us oxygen the same way that green plants on land give us oxygen.r and other foods, using the energy from light [photons]. Plants make sugar and other foods from Carbon Dioxide and Water.

Plants use 6 molecules each of CO₂ + H₂O to make 1 molecule of sugar [C₆H₁₂O₆] and 6 molecules of water [H₂O]. Can you add up the atoms on each side to see if the equation is balanced?

Wow - this website says 70% of the oxygen in our atmosphere comes from plants in the ocean, and only 28% comes from plants on land:
save the plankton

"Save the Plankton, Breathe Freely - National Geographic Society"

Here's a link about seaweed:
"What is seaweed? - NOAA's National Ocean Service" seaweed

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