Types of Microalgae Explained: Spirulina, Chlorella, Euglena and More

Spirulina and chlorella get most of the attention, but they are two members of an enormous family. Microalgae include an ancient cyanobacterium, green cells wrapped in tough walls, a swimming cell that photosynthesizes, red-orange pigment factories and the organisms behind algae-based omega-3 oil. This guide sorts them out: what each type is, where it sits on the tree of life, what it is used for, and what the research does and does not show.

ENERGYbits® • Algae Education

What counts as a microalga

Algae fall into two broad groups: macroalgae, which are the seaweeds you can see and hold, and microalgae, which are typically single cells or small clusters of cells [5]. Microalgae grow in fresh and salt water, multiply quickly, and build biomass from sunlight, carbon dioxide and nutrients. EUFIC, the European Food Information Council, notes that more than 50,000 microalgal species have been described, although only a small number are used in food [5].

That number matters for one reason: when someone says “microalgae,” they could mean anything from a pond-dwelling cell sold as a protein powder to a marine organism grown in fermentation tanks for oil. The label describes a size and a lifestyle, not a nutrition profile. Spirulina and chlorella are both microalgae, yet they differ as much from each other as a lentil differs from an almond.

Two kingdoms of life: cyanobacteria and eukaryotic algae

The most useful distinction in the whole topic is cell type. A recent review of algae grouped under one heading describes them as mostly autotrophic organisms and notes that they include prokaryotic cyanobacteria alongside many eukaryotic algae [2]. Prokaryotic cells have no nucleus or other membrane-bound organelles; eukaryotic cells have both.

Spirulina is on the cyanobacterial side. Chlorella, Euglena, Haematococcus, Dunaliella and Nannochloropsis are eukaryotic [2]. This is why spirulina is sometimes called a blue-green alga while chlorella is a green alga, and it explains differences in pigments and cell structure that show up later in this article. Strictly speaking, cyanobacteria are bacteria that photosynthesize, but they have been called “algae” for so long that the word stays in common use, including in this article and on our own site. If the algae-versus-seaweed question is what brought you here, our guide Is spirulina a seaweed? covers it in depth.

Spirulina: the cyanobacterium

Spirulina is a filamentous, spiral-shaped cyanobacterium. A 2024 review in Foods by Sinetova and colleagues describes it as an ancient edible cyanobacterium and untangles its naming: the common name “spirulina” has been applied to organisms in three genera, Spirulina, Arthrospira and Limnospira, with Limnospira now referring to the strains used for industrial production [1]. That is why labels may say Arthrospira platensis, Limnospira or simply spirulina. For a species-level comparison of the two best-known strains, see our post on spirulina platensis vs maxima.

What it is known for

Spirulina is valued as a protein-dense whole food. In a comparison table in a 2022 review, Arthrospira platensis protein ranged from 50 to 70 percent of dry matter, the highest range among the species it listed [3]. It also contains phycocyanin, the blue pigment that gives it its color, along with chlorophyll, vitamins and minerals. A calculation based on that range: an ENERGYbits serving of 30 tablets at 250 mg each is 7.5 g, which would carry roughly 3.75 to 5.25 g of protein if the biomass fell within that 50 to 70 percent range. Actual values vary by batch and are best confirmed on the product label.

What human research shows

Randomized-trial evidence for spirulina is comparatively deep. A 2021 meta-analysis of five randomized trials (230 participants, doses from 1 to 8 g a day, 2 to 12 weeks) reported lower systolic and diastolic blood pressure with spirulina, particularly in people with hypertension, while calling for more trials [8]. A 2023 dose-response meta-analysis pooling 20 studies and 1,076 participants concluded that spirulina supplementation improved blood lipid measures, including LDL cholesterol [9].

Chlorella: the green alga with a wall

Chlorella is a spherical, single-celled green alga and a eukaryote. Its defining feature is a rigid, multilayered cell wall. Researchers describe that wall as a dense network of carbohydrates and glycoproteins that makes disruption necessary to reach the contents [12], which is why chlorella is sold with a cracked cell wall. ENERGYbits chlorella is made that way; our explainer on broken cell wall chlorella goes deeper.

Compositionally, chlorella is more variable than spirulina. The same 2022 comparison table lists Chlorella vulgaris protein at 12 to 44 percent of dry matter and lipid at 22 to 46 percent, a wide spread that reflects different strains, growth conditions and sources [3]. It is a reminder that numbers for “chlorella” in general should not be assumed for any specific product.

What human research shows

A meta-analysis of 19 randomized trials with 797 participants found that chlorella supplementation lowered total cholesterol, LDL cholesterol, blood pressure and fasting glucose, and that effects were clearer at doses above 4 g a day and durations of 8 weeks or more [10]. A separate 2022 analysis of 10 trials in 539 adults reported reductions in total and LDL cholesterol [11]. As with spirulina, authors call for more precise trials, and the 2022 analysis noted that only two included studies reported the purity and potency of the chlorella used [11].

Euglena: part plant, part swimmer

Euglena gracilis is a single-celled organism that photosynthesizes like a plant but also swims with a whip-like flagellum. It has no rigid cell wall of the kind chlorella has. Its claim to fame in nutrition is paramylon, a beta-1,3-glucan carbohydrate that the cell stores as an energy reserve [2]. In the comparison table, Euglena gracilis protein ranged from 41 to 47 percent of dry matter, with carbohydrate at 34 to 43 percent, a profile noticeably more carbohydrate-heavy than spirulina [3].

Euglena also has real human-trial data. In a 2025 double-blind, placebo-controlled trial in healthy Japanese adults, eight weeks of daily Euglena gracilis in capsules was associated with significantly fewer cumulative days with cold-like symptoms than placebo [6]. A larger 2026 trial in Nutrition Journal randomized 200 adults to 1,000 mg a day of Euglena or placebo for eight weeks; the Euglena group showed higher CD86 expression on plasmacytoid dendritic cells, an immune-cell activation marker, and a lower incidence of cold-like symptoms in exploratory outcomes, with no adverse events reported [7]. These are early and come from one research group, so replication will matter. On the regulatory side, a Euglena gracilis-derived postbiotic ingredient received European novel food authorization in 2024 following a positive EFSA opinion [13].

Haematococcus and Dunaliella: the pigment specialists

Haematococcus (astaxanthin)

Haematococcus lacustris, long known as Haematococcus pluvialis, is a freshwater green alga recognized as a major natural source of the red carotenoid astaxanthin [2]. Under stress, the cells accumulate astaxanthin and turn red. It is a specialist: its value is a single pigment, typically delivered as an extract or oil in small amounts, rather than a whole-food protein source. If you see astaxanthin on a label, this alga is usually where it came from.

Dunaliella (beta-carotene)

Dunaliella salina is a salt-loving green alga best known for beta-carotene [2]. In the comparison table, beta-carotene levels reported for Dunaliella bardawil were 0.8 to 1.5 mg/g, while protein sat at 29 to 31 percent of dry matter [3]. Like Haematococcus, it is mostly used as a pigment source or ingredient rather than as a daily whole-food staple.

Nannochloropsis and Schizochytrium: the omega-3 makers

Fish get their omega-3 fats from the algae they eat, which is why algae are the original source. Nannochloropsis species are marine microalgae reported to be rich in EPA, an omega-3 fatty acid [2]. Schizochytrium is reported as a source of DHA, the other major marine omega-3, and is widely used to make algal oil [2]. A footnote in the Marine Drugs review notes that classifying Schizochytrium as a microalga is itself debated [2]; it is typically grown in fermentation tanks rather than relying on sunlight like the other algae here. That is a good example of how loose the word “microalgae” can be.

Algal oil is a practical choice for people who avoid fish. In one example, a randomized trial in 160 lactating women found that 200 mg a day of DHA from algal oil for eight weeks raised breast-milk DHA concentrations compared with placebo [14]. Whole spirulina and chlorella are not meaningful DHA or EPA sources, so these oils are a different product for a different purpose.

Microalgae vs macroalgae (seaweed)

Macroalgae are multicellular seaweeds such as kelp, nori and dulse, harvested from coastal waters. Microalgae are cultivated in ponds, tanks or photobioreactors. EUFIC notes that seaweed is a long-standing staple in parts of Asia, while microalgae are less common in diets, and that macroalgae such as kelp can contain high iodine levels that may affect thyroid health [5]. That iodine point is one reason seaweed and microalgae are not interchangeable.

Side by side: composition and uses

The table below uses ranges published in a 2022 review of microalgae in foods. Ranges are wide because strain, growth conditions and processing all change the result, so treat them as orientation rather than as specifications for any product.

A 2025 review in Foods examining spirulina, chlorella, Haematococcus and Nannochloropsis reached a useful conclusion: the authors argue whole microalgal biomass may work better than isolated compounds, and that processing such as cell wall disruption can improve bioavailability, while production cost, taste and regulation remain challenges [4].

Where ENERGYbits spirulina and chlorella fit

ENERGYbits focuses on two microalgae because they are the best-studied edible whole-food types: spirulina, a cyanobacterium, and chlorella, a green alga. That pairing is a sensible way to cover both branches of the tree: the cyanobacterial branch with its protein and phycocyanin, and the eukaryotic branch with chlorophyll and a cracked cell wall for digestibility. Both are single-ingredient whole foods with no fillers or additives, grown in freshwater, gently dried at low temperatures and third-party tested for purity and contaminants.

• ENERGYbits spirulina: the cyanobacterium, in 250 mg tablets. A full serving is 30 tablets, or 7.5 g.
• ENERGYbits chlorella: the green alga, made with a cracked cell wall.
• VITALITYbits spirulina and chlorella blend: both algae in one product, for people who want the two branches together.

Not covered by ENERGYbits are the specialist microalgae above, such as Haematococcus extracts or algal omega-3 oils. They serve different purposes, and we would rather say so plainly than blur the categories. For a related read on species, see our guide to the best algae to eat, and for amounts, our spirulina dosage guide.

Safety and sourcing, briefly

Spirulina and chlorella are generally well tolerated, and some people notice mild stomach upset when starting. Check with your healthcare provider first if you are pregnant or nursing, have phenylketonuria, have an autoimmune condition, have a bleeding disorder or take blood thinners or immunosuppressants, or have thyroid or iodine concerns (relevant to chlorella). Sourcing matters for any microalga: because they are grown in water, quality depends on where and how they are cultivated and tested, which is why ENERGYbits products are third-party tested for purity and contaminants.

Also note that new or unusual microalgae sold as supplements may not have the long record of use that spirulina and chlorella do. Regulators assess each new species separately [5].

Conclusion

Microalgae are not one food but a family with distinct branches, each with its own strengths. Spirulina is a protein-dense cyanobacterium; chlorella is a green alga whose wall is cracked to open it up; Euglena is a swimming cell with a distinctive beta-glucan; Haematococcus and Dunaliella are pigment specialists; and Nannochloropsis and Schizochytrium make the omega-3 oils that plant-based eaters rely on. Knowing which is which makes labels easier to read and claims easier to question.

If you would like to start with the two best-studied whole-food microalgae, read about ENERGYbits spirulina or the VITALITYbits spirulina and chlorella blend, which brings both together. They are single-ingredient products with no fillers or additives, freshwater-grown, gently dried at low temperatures and third-party tested for purity and contaminants.

Frequently asked questions

What is the difference between microalgae and macroalgae? +

Microalgae are single cells or small clusters of cells, while macroalgae are multicellular seaweeds such as kelp. Microalgae are grown in ponds, tanks or photobioreactors, and seaweed is typically farmed or harvested in coastal waters [5].

Is spirulina an alga or a bacterium? +

Spirulina is a cyanobacterium, a photosynthetic bacterium, though it is commonly called blue-green algae. It differs from chlorella, which is a eukaryotic green alga [1][2].

Is chlorella a cyanobacterium? +

No. Chlorella is a eukaryotic green alga with a nucleus and a rigid cell wall. Spirulina is the cyanobacterium [2][12].

What is Euglena? +

Euglena is a single-celled organism that photosynthesizes and swims. Euglena gracilis contains paramylon, a beta-1,3-glucan, and has been studied in human trials for cold-like symptoms and immune markers [2][6][7].

What is astaxanthin and which alga makes it? +

Astaxanthin is a red carotenoid. Haematococcus lacustris (formerly H. pluvialis) is recognized as a major natural source and accumulates it under stress [2].

Which microalgae are highest in protein? +

In a 2022 comparison of species, Arthrospira platensis (spirulina) had the highest range at 50 to 70 percent of dry matter, while chlorella ranged from 12 to 44 percent [3]. Ranges vary by strain and conditions.

Do spirulina and chlorella contain omega-3 like algal oil? +

Not in meaningful amounts for omega-3 purposes. Algal omega-3 oils come from species such as Nannochloropsis (EPA) and Schizochytrium (DHA) [2]. Spirulina and chlorella are valued for protein and chlorophyll.

Is Schizochytrium really an alga? +

It is debated. A review footnote notes that classifying Schizochytrium as a microalga is controversial [2]. It is typically grown in fermentation rather than with sunlight.

How many species of microalgae are there? +

EUFIC reports more than 50,000 microalgal species in fresh and salt water, though only a handful are authorized or widely used as food [5].

Is microalgae the same as seaweed? +

No. Seaweed is macroalgae, while microalgae are microscopic. Kelp can contain high iodine, which EUFIC notes may affect thyroid health, while microalgae generally contain less [5]. See our guide on whether spirulina is a seaweed.

What does human research say about spirulina and chlorella? +

Meta-analyses of randomized trials report lower blood pressure and improved lipids with spirulina [8][9], and lower cholesterol, blood pressure and fasting glucose with chlorella [10][11]. Authors call for larger, better-controlled trials.

How many ENERGYbits tablets are a serving? +

Each ENERGYbits tablet is 250 mg and a full serving is 30 tablets, or 7.5 g. Trial doses of spirulina and chlorella have varied, and these figures are not a dose recommendation [8][10].

Who should check with a provider before taking algae? +

People who are pregnant or nursing, or who have phenylketonuria, an autoimmune condition, a bleeding disorder, or thyroid or iodine concerns, and anyone taking blood thinners or immunosuppressants, should consult their healthcare provider first.

This article is for educational purposes only and is not medical advice. These statements have not been evaluated by the FDA. ENERGYbits® products are whole-food supplements and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your doctor before starting any supplement, especially if you are pregnant, nursing, taking medication, or managing a medical condition.

References

1. Sinetova MA, Kupriyanova EV, Los DA. Spirulina/Arthrospira/Limnospira: three names of the single organism. Foods. 2024;13(17):2762. https://doi.org/10.3390/foods13172762
2. Perkovic L, Djedovic E, Vujovic T, Bakovic M, Paradzik T, Coz-Rakovac R. Biotechnological enhancement of probiotics through co-cultivation with algae: future or a trend? Mar Drugs. 2022;20(2):142. https://doi.org/10.3390/md20020142
3. Hernandez H, Nunes MC, Prista C, Raymundo A. Innovative and healthier dairy products through the addition of microalgae: a review. Foods. 2022;11(5):755 (Table 1). https://doi.org/10.3390/foods11050755
4. Guil-Guerrero JL, Prates JAM. Microalgae bioactives for functional food innovation and health promotion. Foods. 2025;14(12):2122. https://doi.org/10.3390/foods14122122
5. EUFIC. Microalgae: what are they and how to grow and use them. Updated 2 February 2023. https://eufic.org/en/food-production/article/microalgae-what-are-they-and-how-to-grow-and-use-them
6. Nakashima A, Suzuki K, Nagata M, Takara T. Euglena gracilis suppresses cold symptoms in healthy individuals: a double-blind, randomized, placebo-controlled trial. Food Sci Nutr. 2025;13:e70935. https://doi.org/10.1002/fsn3.70935
7. Nakashima A, Okamoto W, Marukawa-Hashimoto Y, Takara T. Incorporating Euglena gracilis into the habitual diet modulates immune function and reduces common cold-like symptoms: a randomized controlled trial. Nutr J. 2026;25:90. https://doi.org/10.1186/s12937-026-01350-6
8. Machowiec P, Reka G, Maksymowicz M, Piecewicz-Szczesna H, Smolen A. Effect of spirulina supplementation on systolic and diastolic blood pressure: systematic review and meta-analysis of randomized controlled trials. Nutrients. 2021;13(9):3054. https://doi.org/10.3390/nu13093054
9. Rahnama I, Arabi SM, Chambari M, et al. The effect of spirulina supplementation on lipid profile: GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials. Pharmacol Res. 2023;193:106802. https://doi.org/10.1016/j.phrs.2023.106802
10. Fallah AA, Sarmast E, Habibian Dehkordi S, et al. Effect of Chlorella supplementation on cardiovascular risk factors: a meta-analysis of randomized controlled trials. Clin Nutr. 2018;37:1892-1901. https://doi.org/10.1016/j.clnu.2017.09.019
11. Sherafati N, Bideshki MV, Behzadi M, et al. Effect of supplementation with Chlorella vulgaris on lipid profile in adults: a systematic review and dose-response meta-analysis of randomized controlled trials. Complement Ther Med. 2022;66:102822. https://doi.org/10.1016/j.ctim.2022.102822
12. Lopes PA, Coelho D, Prates JAM. Testimony on a successful lab protocol to disrupt Chlorella vulgaris microalga cell wall. PLoS One. 2022. https://doi.org/10.1371/journal.pone.0268565
13. FoodNavigator. Kemin receives novel food authorization for BetaVia Pure. 19 April 2024 (trade press report of EU authorization of a Euglena gracilis-derived ingredient). https://www.foodnavigator.com/Article/2024/04/19/Kemin-receives-novel-food-authorization-for-BetaVia-Pure
14. Yang Y, Li G, Li F, et al. Impact of DHA from algal oil on the breast milk DHA levels of lactating women: a randomized controlled trial in China. Nutrients. 2022;14(16):3410. https://doi.org/10.3390/nu14163410