On a recent fossil collecting trip a friend asked, “What do you think is the most important organism on the Earth?” She knew full well I would answer, “Humans!” since we are the masters of our domain and without rival in the animal world (are we good or what?).

She was a bit surprised, and gave me the “Are you nuts?” look, when, without hesitation, I answered, “No doubt about it… hands down the most important organism on this planet is marine algae.”

blue-green algea
Phytoplankton are tiny microscopic plants – algae – that form the base of the marine food chain. Phytoplankton is most abundant in colder waters where there is an abundance of nutrients. Image: California EPA.

“Algae?!?,” she said.

“Yes, Algae,” I answered. “Do you want an explanation or are you going to take my word on this?” I asked.

“Let me think about it and I’ll get back to you on that one,” she said. As we continued our hunt for shark’s teeth, whale bones and anything else we could find, she finally broke down. “I don’t get it. We can change the world in so many ways…..what has algae done?

“Very simple,” I said. “Algae allow us and almost every other organism you can think of, living or dead, to be here.”

Suddenly, she got that look. You know, the one you get when that light bulb in your head clicks on…bing, there it is! “Ah, oxygen, right?”

“Correctomundo!” was my very scientific reply.


Seaweed are not plants, but are algae. Not only do algae provide much of the Earth’s oxygen, they are also the base for almost all marine life. Green algae get their color from chlorophyll and exist on or near the surface where there is plenty of sunlight. Green algae are not as common in the ocean as brown and red seaweed. It is also more closely related to land plants than any other type of algae. Photo: Fred Hsu, CC Wikimedia

It is estimated that marine plants produce between 70 and 80 percent of the oxygen in the atmosphere. Nearly all marine plants are single celled, photosynthetic algae. Yup, that’s right, good ol’ scum on the pond…green gak…..slip slimein’ away. Even marine seaweed is many times colonial algae. They are a bunch of single cells trying to look like a big plant (see seaweed photo), but they are really individuals.

We need marine algae a whole lot more than they need us. Think about it, 70 percent to 80 percent of all the oxygen we breathe comes from algae! Without them we would really be sucking wind, but not for long! At this point, you may be saying, “Yo! What about the trees and other land plants?” Trees and other land plants are very important, no doubt about it. But for pure survival, we couldn’t make it without algae.

Why does so much of our oxygen come from algae? First of all, remember that the oceans cover about 71 percent of this planet and land is only about 29 percent. If we assume that every square mile of the ocean produces as much oxygen as every square mile of land, then this makes sense. The oceans would produce about 71 percent and the land 29 percent of the oxygen we breathe. Looks like we are in the ballpark, don’t you think?


Now the question is, “Are the oceans, indeed, as productive as the land?” At first you might not think so, after all when you look at the land there are trees, bushes and grass and all kinds of plants growing. They must crank out oxygen to beat the band! They do, but also remember that there are many places on land that don’t have much in the way of plants. How about Antarctica or the Sahara Desert along with many others? These are good-sized chunks of real estate where plants are rare. How much oxygen is being pumped out in these areas? Some areas on land have an abundance of plants and produce a large quantity of oxygen, while others have very few plants and produce very little.

rainforest, jungle, photo: Lucas Pezeta
Rainforests are the oldest living ecosystems on the planet. They cover 2 percent of the Earth’s surface or 6 percent of land, and are an important source of oxygen. They also are home to many of the Earth’s plant and animal species, but they also play a vital role in sustaining life beyond their ecosystems as they help regulate global climate and water cycle. Pictured above is a small section of the Brazilian rainforest, the Earth’s largest. 
Photo: Lucas Pezeta, Pexels

The same can be said for the oceans. There are some areas that have an abundance of algae living in the waters and other areas that don’t. In the ocean, there are areas of upwelling where cold, nutrient rich bottom water moves toward the surface. These upwelling waters mix with the surface water and produce an area that is like liquid fertilizer for plants. They go ballistic and there are billions of the little critters in the water just pumping out oxygen left and right. Other areas of the oceans don’t have much in the way of nutrients in the water and they are like the deserts on land with very few plants.

Overall, the production of oxygen in the oceans is at least equal to the production on land, if not a bit more. Plants on land are easy to spot. Plants in the ocean are a bit more difficult to see since they are single cells floating in the water. Even though you may not see them, they are there. Remember, these little cells go down to over 300 feet below the surface so they have lots of room to spread out.

Kelp is a type of marine algae, or seaweed. Seaweeds come in three different color varieties, red, green and brown. Kelp is a kind of brown seaweed that grows to be very large. Although kelp resembles a kind of weed or tree, it is quite different from plants that grow on land. Photo: NOAA

Plants on land and in the ocean are extremely important to us and we wouldn’t be here without them. Land plants provide us (and other critters) with food, raw materials like wood and fiber to make cloth and paper. They protect the land from erosion with their roots, provide beauty and shade on a hot day and produce oxygen as an added bonus although we could probably survive with the oxygen.

Marine plants are also used as food, but we tend to forget about them because they are so small and difficult to see. But remember, the next time you wake up in the morning, stretch and open wide with that big morning yawn, that breath of fresh air you are getting is due for the most part to our friend, the algae. If we kill them by polluting the oceans, we are also killing our vital lifeline.


There are more than 7,000 different species of algae. Most live in the oceans, but they also live in fresh water and even on land. Also, algae produce about 330 billion tons of oxygen each year.

There are three types of algae: red, green and brown. Some algae in the ocean are very small and drift in the ocean water. Those algae are phytoplankton. The most abundant type of algae is brown algae, with over 5,000 species (not all are totally brown). Red algae has over 2,000 species, and lives where light is dim, in deeper waters, mostly in temperate and tropical waters. Green algae are more common on land and in fresh water systems, but are the least common in the ocean where about 800 are known to exist.