The Ocean's Unsung Heroes

Big or small, slimy and sometimes leafy, algae are found in almost every aquatic environment and are at the base of the food chain, making them a crucial food source. Thousands of different species fall under the umbrella term "algae." Algae can be broken into two groups: microalgae (phytoplankton) and macroalgae (seaweed). Phytoplankton are tiny, single-celled organisms seen with a microscope, while seaweed (brown, red or green) are larger and multi-celled organisms.

Algae are massively important to the production of oxygen. Along with a tiny plant-like marine bacteria called Prochlorococcus, algae help produce about half of the oxygen on Earth! While algae are key to maintaining life-sustaining oxygen levels, they technically aren't even plants but protists. Algae absorb nutrients directly from the water and don't have stems or leaves, produce fruits or seeds, or have the same kind of roots as plants, even though both plants and algae photosynthesize. But algae's hidden talents don't stop there. Let's take a closer look at three kinds of algae to see what makes them the ocean's unsung heroes.

Sargassum: Floating Through Life

Unlike most seaweed, two species of sargassum live free-floating in large masses on the ocean's surface. This brown macroalgae is kept afloat by pneumatocysts, which are small and round structures mostly filled with oxygen. Pneumatocysts keep sargassum buoyant in bright ocean surface sunlight, helping with photosynthesis. Eventually, pneumatocysts lose their gas, and the sargassum sinks to the ocean floor and breaks down, providing food for deep sea creatures.

Despite its tranquil appearance from above, sargassum conceals a lively underwater habitat. One dominant sargassum species primarily grows on the surface of the Sargasso Sea—a portion of the Atlantic Ocean surrounded by four ocean currents, including the Gulf Stream. Known for its calm waters and abundance of sargassum, the Sargasso Sea is like a sargassum factory where mats of this brown algae are pulled into the surrounding currents and carted off into the wider ocean. Masses of sargassum can stretch for miles and miles, making it a floating hub of fish activity. Creatures like the sargassum fish, sargassum swimming crab and sargassum shrimp live in the brown seaweed their whole lives, while temporary visitors like seabirds, dolphins and large predatory fish like tuna and mahi-mahi forage for prey hiding in sargassum's cover. In the past 10 years, scientists have also learned that another animal spends the first years of its life in sargassum—baby sea turtles.

A Baby Sea Turtle's Haven

Out in the Sargasso Sea, scientists have recently discovered baby sea turtles seeking refuge in the brown seaweed. These first couple years of a sea turtle's life remained a mystery until scientists successfully tracked some hatchlings. After breaking out of their eggs in places like Florida beaches, species like the loggerhead and green sea turtle enter the Gulf Stream current to journey to the Sargasso Sea. Here, baby sea turtles spend years hiding from predators among sargassum and learning to find food before leaving their floating refuge for the open ocean.

Protecting Baby Sea Turtles

Excessive growth of sargassum can prove dangerous for sea turtles, however. Due to human-caused climate change and pollution, an overgrowth of sargassum is smothering Florida beaches. Warming waters and polluted stormwater runoff are increasing the amount of nitrogen and phosphorous in the ocean, causing sargassum to grow at an alarming rate and wash up on shores in huge mats. In addition to smelling terrible, these mats block baby sea turtles' paths to the ocean, making them easy meals for predators. Reducing our carbon footprint and pollution levels will help keep baby sea turtles safe and give them a fighting chance out in the ocean, stowed away in miles of sargassum.

Kelp: A Helpful Macroalgae

Diving beneath the waves, we find kelp, another brown seaweed. Kelp is made up of large, flexible leaves called blades attached to stems called stipes. Bulbous air bladders where the blades and stipes meet keep kelp afloat, and root-like holdfasts affix kelp to rocks on the sea bottom. As a result, kelp fronds grow vertically, creating large kelp forests, an essential habitat in cool coastal waters off the west coast of North America.

Species like giant kelp grow exceptionally fast—up to two feet a day—with some reaching 150 feet. Kelp grows toward the water's surface, forming a canopy with other kelp to create their underwater forest. Like clumps of sargassum, these kelp forests offer food and shelter for many aquatic animals, such as sharks, lobsters, squids and more. At the National Aquarium, guests can visit a recreated kelp forest in the North Atlantic to the Pacific exhibit to see animals that live in kelp habitat, like striking California moray eels and bright orange garibaldi.

There's Kelp in Toothpaste?

From frozen treats to toiletries to pharmaceuticals, kelp is in more products than you think! Kelp contains an agent called algin, which keeps different liquids mixed, binds materials together, thickens mixtures and more, making it a versatile ingredient in edible and inedible products.

Kelp is also rich in vitamins and nutrients, like calcium and magnesium, and tastes delicious, making it an excellent addition to any balanced diet. Species like giant kelp can be eaten whole, either cooked or raw, making it a great contender for the star of a meal. Its distinct umami taste gives it a meaty flavor, and its saltiness pairs well with seafood. Kelp is also easy to farm because it doesn't require much maintenance and grows quickly, opening the door for sustainable farming.

Kelp-ing It Cool

Because it thrives in cold water, rising ocean temperatures due to climate change are deadly for kelp. The warming ocean, combined with pollution and commercial harvesting, has also increased kelp-hungry purple sea urchin populations. In recent years, a population explosion of purple sea urchins has decimated large areas of kelp forest habitat. Urchins' natural predators, sunflower sea stars and otters, have declined in number because of disease exacerbated by climate change and hunting, respectively. As a result, urchins run rampant, feasting on all kelp in sight, with each spikey creature living and eating for decades.

Coccolithophore: Tiny and Mighty

Grab your microscopes, and let's investigate the microalgae coccolithophore! Coccolithophores are microscopic phytoplankton known for hard outer layers that form a sphere. The layers are made of calcium carbonate scales, or plates, known as coccoliths. Like other algae, they contribute a significant amount of oxygen through photosynthesis. And chances are good you've interacted with them before! Coccoliths are found in ordinary blackboard chalk used in classrooms because chalk is made of fossilized protists, like coccolithophores.

Influencing Ocean Temperature One Microscopic Organism at a Time

Great power is stored in these influential microscopic organisms, especially when in a big group. Although coccolithophores can be difficult to study, scientists know quite a bit about species that are easy to grow in a lab. These species can grow massive blooms in temperate and freezing water, affecting ocean chemistry and global climate.

When coccolithophores form, they absorb dissolved carbon dioxide from the water—some of it produced by decomposing animals—to create their calcium carbonate coccoliths. In other words, coccolithophores act like a carbon sink, naturally storing carbon. At the end of their life cycle, coccolithophores also minimize the amount of carbon dioxide in the ocean that reenters the atmosphere—an important element of combatting climate change.

Minimizing Ocean Acidification

Coccolithophores are also negatively impacted by climate change. Ocean acidification, caused by atmospheric carbon dioxide gas dissolving into the ocean, makes the ocean more corrosive. The acidity can make it difficult for coccolithophore populations to grow because of the extra energy needed to grow their calcite shells, which limits their ability to grow or reproduce.

Climate change also affects other kinds of phytoplankton by fostering algal blooms. While blooms of coccolithophores positively impact the environment, most algal blooms are caused by warming waters and excess nutrients that make algae grow quickly. Algal blooms can change the color of the water, release toxins and dangerous gases when they die, block sunlight and use up too much oxygen, killing other aquatic creatures. Harmful algal blooms are often caused by phytoplankton like dinoflagellates and diatoms that feed on excess nutrients in the water, such as phosphorus and nitrogen. A primary source of these excess nutrients is polluted stormwater runoff draining off the land into rivers that flow into the ocean. Actions like planting winter cover crops in agricultural fields, upgrading water treatment plants and planting trees help reduce the nutrients that fuel harmful algal blooms. Mitigating out-of-control blooms and protecting coccolithophores may be crucial due to their effect on ocean chemistry and temperature.

Doing Our Part

The benefits of algae can be found everywhere, from absorbing carbon to protecting tiny baby sea turtles to forming products we use in our everyday lives. However, too much algae can hurt the environment. By reducing our pollution, we can combat climate change to mitigate harmful algal blooms and overproduction of seaweed like sargassum. Minimizing our footprint will keep phytoplankton and seaweed healthy and hospitable for other ocean creatures for years to come.