Have you ever felt the tangle of seaweed around your ankle when wading in the water? For many beachgoers, it’s enough to send them scrambling for shore. For them, the most common words used to describe seaweed are “slimy” and “disgusting.”
If you’re one of those people, over the next three minutes, I hope to change your mind—for seaweeds, in addition to being the most common plant forms on earth, are both beautiful and necessary for life.
“Seaweed" is a common name for marine plants and algae, but marine scientists use the word macroscopic algae. Macroscopic, multicellular, benthic marine algae, to be precise.
Some algae are microscopic, like the phytoplankton. Some are huge, like giant kelp. Most, however, fall somewhere in between, in saturated hues of green, red and brown.
In all of its various forms, seaweed is the cornerstone of life on Earth.
Did you know that three of your next five breaths come to you courtesy of phytoplankton, the tiny marine algae that produce most of the planet's oxygen? In fact, it’s because of phytoplankton's production of oxygen that air-breathing life exists. That means us!
California's giant kelp, is arguably the classic example of seaweed. It grows in undersea forests and appears to have roots, a trunk and even leaves. But in fact, macro algae have none of these things.
For roots, they have what marine scientists call holdfasts. Their branches are called stipes, and their leaves are fronds. Many function in very similar ways to their terrestrial analogs, with one key difference: The holdfast is the plant’s anchor—it has no role in taking up nutrients the like the roots of a land plant. That process occurs throughout the kelp stalk.
Many macro algae also have the addition of special structures called floats or air bladders. They’re the plant's little life jackets, keeping it buoyed up and near the surface of the water, near the sunlight that it needs to grow.
And grow they do. Giant kelp can grow up to 2 feet per day, faster even than bamboo.
But, macro algae can live only as deep as sunlight can penetrate. Where the water is clear, such as in Hawaii or the Caribbean, algae can grow at depths of up to 800 feet.
Red algae grows best in the deep and can appear almost black due to a high concentration of a red pigment in its cells that helps the plant absorb blue light.
You’ve likely eaten algae. Nori, which holds together sushi rolls, is from the genus porphyra. Carageenen, derived from red algae, is added to ice cream, sauces and even beer, to which it adds a smoother, more viscous texture.
And your car is probably burning old algae. That’s right; much of the oil we use comes mostly from cretaceous deposits of marine algae.
In the future, you might also refuel on algae. Researchers have "cooked" algae in water to produce a kind of light sweet crude biofuel. Produced on a large scale, algal biofuel could bring the price of gas down, reduce our carbon footprint and hugely raise algae's stature.
Artist Josie Iselin recently released a book titled “An Ocean Garden: The Secret Life of Seaweed,” which shows the myriad forms and brilliant colors of algae she found simply by beachcombing near her home. She’s allowed us to post some of these stunning photos on our website, aqua.org/ablueview. Give it a look. I guarantee you’ll never look at seaweed the same way again.
This is John Racanelli of the National Aquarium for WYPR, your NPR news station.