Algae 101

The first step toward recognizing the commercial, societal, and environmental value of algae is understanding what algae are in the first place. Most people have a sense of what they are, but defining them clearly, and understanding how many different kinds are out there, is trickier. So we put together this brief primer to help our friends, partners, customers, and anyone who is interested get up to speed. We hope you enjoy it, and if you have any questions, don’t hesitate to reach out to us!

What is Algae?

Algae are plant-like organisms that live mostly in water and make their own food through photosynthesis. They can be microscopic or large like seaweed. However, unlike regular plants, algae do not have roots, stems, or leaves.

Microalgae

Microalgae are invisible-to-the-eye, photosynthetic organisms that you can find in freshwater, brackish, and marine environments, or even in the pond in your backyard or your fish tank. They are incredibly diverse and come in different shapes, sizes, and colors (see below). They are important because they form the base of aquatic food webs and can be used to make eco-friendly versions of many of the products we rely on every day.

Macroalgae

Macroalgae are larger, multicellular algae — commonly known as seaweeds — that thrive along the continuum from freshwater to the ocean and are often used in food, fertilizers, and industrial products.

Types of Algae

Diatoms (Bacillariophyta)

These are unicellular eukaryotic (cells with a true nucleus) microalgae that have beautiful distinctive silica shells called frustules that contribute significantly to global oxygen production (approximately 20% to 30%)¹. They are golden brown in color because of the production of the pigment fucoxanthin and chlorophyll c. They’re found in both freshwater and marine environments, and some of them are known to produce toxins².

Green algae (Chlorophyta)

These include both unicellular eukaryotic microalgae and multicellular macroalgae that are commonly found in both freshwater and marine environments. They are close relatives of land plants and bright green due to the production of the pigments chlorophyll a and b. Some of the unicellular species have flagella that allow them to swim. One of the types of microalgae (Chlorella) is a trending food supplement that you might even find in the health section of your grocery store. Green macroalgae is also commonly consumed by humans; for example “sea lettuce” (Ulva) is often eaten fresh or dried in soups and salads in Asian cuisine.

Blue-green algae (Cyanobacteria)

These are prokaryotic (simple cells without a true nucleus) microalgae found in both freshwater and marine environments. They are technically bacteria but photosynthetic. In fact, they were the first organism to perform oxygenic photosynthesis. Some of them (e.g., diazotrophs) are capable of fixing atmospheric nitrogen gas³, while others can produce toxins⁴. They are collectively called “blue-green algae” because the first ones discovered produce chlorophyll a (green) while others produce phycocyanin (blue pigment). However, depending upon the pigments they produce, cyanobacteria can also be pink or the color of Mountain Dew^®. You can also find at least one type (Spirulina) in the health section of your grocery store.

Dinophyta (Dinoflagellates)

These are unicellular eukaryotic microalgae with flagella that allow them to swim with a spiraling motion. Depending on the species of dinoflagellates, they can be photosynthetic or not. Their morphology varies depending on the species and lifecycle of a given species, with some of them have an armored, cell covering structure called a theca. Dinoflagellates possess the green pigment chlorophyll a, as well as golden brown pigments such as fucoxanthin and peridinin. While some of them have a bad reputation for causing harmful algal blooms, such as the red tides⁵, some of them are known for their beauty, like those that are magnificently bioluminescent (glow in the dark)⁶.

Rhodophyta (Red algae)

These are often multicellular eukaryotic macroalgae; however, there are some unicellular microalgae as well. While green chlorophyll a is their main photosynthetic pigment, they also possess phycoerythrin, which gives them their distinct deep red color. Unlike dinoflagellates and some green algae, unicellular members of red algae do not possess flagella and hence lack the ability to swim. While they are predominantly found in marine environments, some of them also inhabit freshwater systems. Some macroalgae members are also consumed as food in the form of Nori for sushi or in soups and salads in Asian cuisine.

Chrysophyta (Golden algae)

These are unicellular eukaryotic microalgae found in freshwater and marine environments. They contain the green pigment chlorophyll a, but also the golden brown pigment fucoxanthin and other carotenoids that gives them their characteristic color. They are close relatives to diatoms and can cause “golden tides” in lakes. One of them, Prymnesium parvum), also produces toxins that are linked to fish kills⁷.

Brown macroalgae (Phaeophyceae)

These are some of the largest multicellular macroalgae commonly found in marine and rocky coastlines. Their characteristic brown color comes from the pigment fuoxanthin (also found in Diatoms, dinoflagellates, and chrysophyta). They form underwater “forests” that are home for many marine organisms. They have been already used as fertilizers⁸ and soil amendments⁹. And similar to the green and red forms of macroalgae, they have been consumed fresh or dried in soups, salads in Asian cuisine.

History

Cyanobacteria (commonly called blue-green algae) have been on Earth for over 3.4 billion years, and played a key role in transforming the planet’s atmosphere⁸. Before cyanobacteria evolved, Earth’s atmosphere was dominated by nitrogen, carbon dioxide, methane, and other volcanic gases with almost no oxygen. Through photosynthesis, ancient cyanobacteria produced and released oxygen, leading to the Great Oxygenation Event, which paved the way for the evolution of life as we know it now, including microalgae and, later, macroalgae. Microalgae are also essential to the base of aquatic food webs. As the chefs of the ocean, they are the major drivers of carbon and nutrient cycling in oceans and freshwater systems.

In addition to supporting life, microalgae has literally fueled economic prosperity throughout human civilization. For example, the sedimented organic remains of microalgae that proliferated in ancient oceans and lakes transformed under high pressure and heat over millions of years into fossil fuels (notably petroleum, natural gas, and oil shale)^9,10,11,12. Thus, much of the world's crude oil is, in fact, derived from ancient algal deposits.

The idea of microalgae and macroalgae as food and health supplements is far from modern. Ancient civilizations like the Aztecs harvested Spirulina from Lake Texcoco as a high-protein food source^12,13. The Kanembu people collected Spirulina from Lake Chad and dried it into flat cakes called “dihe”¹⁴. Another cyanobacterium Nostoc, called “fa cai” in Mandarin and “fat choy” in Cantonese, were wild-harvested and used in soups in arid regions of western China¹⁵. Similarly, there is evidence of red, green, and brown seaweed consumption in the Mesolithic and Neolithic periods across Europe¹⁶. Archaeological evidence has also been found in Monte Verde in southern Chile for 20 different species of seaweed being consumed approximately 14,000 years ago¹⁷.

From ancient diets and rituals to today’s health supplements and bioindustries, the role of microalgae and macroalgae has only grown. Now algae are being harnessed for everything from:

• superfoods^18,19,20,21
• nutraceuticals^22,23
• biofertilizer^{24,25,26,27,28}
• aquaculture feed^29,30,31
• biofuels^32,33,34
• biomaterials^{35,36,37,38,39}
• wastewater treatment^40,41,42,49
• cosmetics^{43,44,45,46,47}
• cutting-edge pharmaceuticals^48,49,50
• space life support systems^51,52,53

Potential

Today, microalgae are at the forefront of green technology, offering scalable solutions for food, energy, and environmental challenges.

All of this potential has so far been realized using only a handful of species — even though there are thousands of microalgal strains in culture collections that remain unexplored for their biochemical and commercial potential.

Research at Bigelow Laboratory is playing a key role in unlocking the full potential of algae. We invite researchers, students, businesses, innovators, entrepreneurs, and enthusiasts alike to join us in unlocking this untapped diversity. Reach out and be part of the next wave of microalgae discovery!

Looking to get engaged with algae? Click here to learn more about the Maine Algal Research Infrastructure and Accelerator project at Bigelow Laboratory.

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