What Is Microalgae?

Microalgae are microscopic, single-celled organisms that photosynthesise in water. They sit at the base of aquatic food chains, produce an estimated 50-80% of the planet's oxygen, and they are the original source of the long-chain omega-3 fatty acids that fish accumulate through their diet. If you have picked up a supplement labelled "microalgae" in a health shop and wondered what exactly you were holding, this is the subject.

The term covers an enormous range of biology. Some estimates put the species count between 200,000 and 800,000, of which roughly 50,000 have been formally described. Fewer than ten are cultivated for food supplements. We work with two of those species daily.

The gap between the broad category name and what actually ends up in your capsule is worth understanding. The nutritional profile, safety record, and practical value differ substantially from one species to another.

What Microalgae Are and Why They Matter Nutritionally

Why Most Microalgae Species Are Irrelevant to Supplements

The microalgae kingdom includes diatoms, green algae, dinoflagellates, and several other phyla. They are found in oceans, lakes, rivers, and damp soil. Most are ecologically important but nutritionally irrelevant to you as a supplement buyer. When we evaluate raw biomass from different species, the compositional range is vast: some are almost entirely lipid, others are protein-dense, and many are neither in useful concentrations.

Of the tens of thousands of described species, fewer than ten have any commercial use in food supplements. The rest remain research subjects or ecological curiosities. This ratio alone should make you sceptical of any product that trades on the broad category rather than naming its species.

That matters because a product labelled "microalgae blend" without naming species is asking you to trust a category that spans hundreds of thousands of organisms. It is a bit like buying "fish" without knowing whether you are getting salmon or sardine. The biology is interesting. The mythology built around the category name is often less useful than the species-level facts.

What Distinguishes Microalgae from Macroalgae

Microalgae are single-celled and microscopic. Macroalgae (seaweed) are multicellular and visible: kelp, nori, dulse, sea lettuce. You can hold a sheet of nori; you cannot see a single microalga without a microscope. They are different organisms with different nutritional profiles. Microalgae are cultivated for omega-3 fatty acids, concentrated protein, and specific pigments. Seaweed is harvested primarily for iodine, trace minerals, and culinary use.

If you are looking for EPA or DHA from a plant source, microalgae is what you need. If you are looking for iodine, seaweed is the better fit. They are not interchangeable in a supplement context, despite both being called "algae" on shop shelves.

Types of Microalgae Used in Supplements

When a supplement label says "microalgae," the species determines what you are actually getting. Plenty of products use the category name as if it were a selling point in itself. It is not. We have tested biomass from multiple species side by side, and the nutrient profiles are so different that grouping them under one name obscures more than it reveals.

Chlorella: The Protein and Chlorophyll Source

Chlorella is a freshwater green microalga, most commonly Chlorella vulgaris or Chlorella pyrenoidosa. Open a tub of chlorella powder and the colour hits you first — a deep, almost startling green, which is the chlorophyll. It is one of the most protein-dense whole foods available, at roughly 50-60% protein by dry weight with a complete amino acid profile.

You will find chlorella sold as tablets, powder, or added to greens blends. If your goal is concentrated plant protein or chlorophyll rather than omega-3, chlorella has a stronger case than most other microalgae species. Our guide to what chlorella is covers it in detail.

Nannochloropsis: The Marine Phytoplankton EPA Source

Nannochloropsis gaditana is a marine microalga and the species most people mean when they say "marine phytoplankton." Its distinguishing characteristic is an unusually high concentration of EPA (eicosapentaenoic acid) relative to total fatty acids.

It also delivers chlorophyll, carotenoids, and amino acids as part of the whole-cell composition. We chose Nannochloropsis gaditana for our marine phytoplankton product specifically because of that EPA concentration. The fatty acid profile stood out when we screened candidate species. Unlike chlorella, it is valued primarily as an omega-3 source rather than a protein supplement.

You can read more in our guide to what marine phytoplankton is and our species profile of Nannochloropsis gaditana.

Schizochytrium: The Algae-Derived DHA Source

Schizochytrium is a heterotrophic microalga. It does not photosynthesise but grows by consuming organic carbon sources in fermentation tanks. It is the primary source of algae-derived DHA (docosahexaenoic acid) in supplements. Most vegan DHA capsules on the market use Schizochytrium oil.

If you see "algae oil" or "algal DHA" on a label, this is almost certainly the species behind it. DHA contributes to the maintenance of normal brain function and normal vision at 250 mg per day (EFSA-authorised health claim under Regulation EU 432/2012). For the differences between EPA and DHA, see our guides to EPA and DHA.

Haematococcus and Dunaliella: Single-Nutrient Microalgae Extracts

Haematococcus pluvialis is grown commercially for astaxanthin, a carotenoid pigment with antioxidant properties. Dunaliella salina is a source of natural beta-carotene. Both are used in supplements but are less common than chlorella or Schizochytrium. You will typically encounter them as single-nutrient extracts rather than whole-food powders.

We considered both during product development and chose not to include them. Astaxanthin and beta-carotene are valuable compounds, but they serve a narrower purpose than the broad-spectrum nutrition you get from whole-cell chlorella or Nannochloropsis. If you are looking specifically for antioxidant supplementation, these species are worth investigating. If you want a nutritional foundation, they are not the starting point.

What Microalgae Contain Nutritionally

What you get from a microalgae supplement depends heavily on the species, the growing conditions, and how the biomass is processed. We see this in our own production: even batch-to-batch variation in light exposure changes the lipid profile.

Broad claims about "microalgae nutrition" are often misleading because they blur the differences between species with very different compositions. If you are comparing products, the species name and the milligrams on the label matter more than any marketing copy about "superfood algae."

Protein and Amino Acids in Microalgae

Chlorella leads the field at 50-60% protein by dry weight, with all essential amino acids present. Nannochloropsis typically contains 30-40% protein. Schizochytrium is lower in protein but is not cultivated for that purpose.

If concentrated plant protein is your priority, chlorella is the relevant species. The category term "microalgae" tells you nothing about protein content without a species name attached.

Omega-3 Fatty Acids from Microalgae

Nannochloropsis produces EPA. Schizochytrium produces DHA. These are the two long-chain omega-3 fatty acids that contribute to the normal function of the heart at a combined daily intake of 250 mg (EFSA-authorised health claim under Regulation EU 432/2012).

Most plant foods provide only ALA (alpha-linolenic acid), which your body converts to EPA and DHA at rates generally estimated below 5-10% (Brenna et al., 2009). That conversion bottleneck is the reason microalgae-derived omega-3 supplements exist.

Fish are not the origin of these fatty acids. They are the middleman. The omega-3 you find in a salmon fillet originates in the microalgae the fish consumed. That is why we regard microalgae as the primary source, not the alternative.

Chlorophyll, Carotenoids, and Pigments in Microalgae

Chlorella is one of the densest known food sources of chlorophyll. Haematococcus produces astaxanthin. Dunaliella produces beta-carotene. Nannochloropsis contains violaxanthin and other xanthophyll pigments. These are part of the microalgae's photosynthetic machinery and carry over into supplements made from whole-cell biomass.

If your supplement is an extracted oil (typical for DHA products), you get primarily the fatty acids. If it is a whole-cell powder, you get the broader spectrum of pigments and micronutrients alongside the lipids. You can usually tell the difference at a glance: an extracted oil is pale gold, while a whole-cell powder carries the deep colour of whatever pigments the species produces.

How Microalgae Are Grown for Supplements

The cultivation method affects purity, nutrient consistency, and price. If you are comparing two microalgae products and one costs noticeably less, the growing system is often the reason.

Closed Photobioreactors for Microalgae Cultivation

Photobioreactors are enclosed glass or plastic tubes where microalgae grow under controlled light, temperature, and nutrient conditions. Because the system is sealed, there is minimal risk of contamination from airborne bacteria, heavy metals, or competing organisms. The biomass that comes out is cleaner and more consistent batch to batch.

The trade-off is cost. Closed systems are substantially more expensive to build and operate than open ponds. That cost shows up at the till, but so does the purity. We accept the higher production cost because the contamination control is not a marketing line; it is the difference between biomass we would use and biomass we would not.

Open-Pond Microalgae Cultivation

Open-pond cultivation is cheaper and easier to scale. The algae grow in large, shallow outdoor pools exposed to sunlight. The trade-off is that the biomass is exposed to whatever is in the surrounding environment: dust, competing microorganisms, variable weather, and heavy metals from the water source.

Many chlorella and spirulina products are grown this way. The cost saving is real, but if purity matters to you, ask the manufacturer about their cultivation method. Silence on this point is itself informative. Our article on how microalgae are grown for supplements covers this in more depth.

How to Read a Microalgae Supplement Label

When you pick up a product that says "microalgae" or "algae," three things are worth checking before you spend your money.

Species name. A label that says "microalgae blend" without naming the species is not giving you enough information to evaluate what is inside. Look for specific names: Chlorella vulgaris, Nannochloropsis gaditana, Schizochytrium sp. The species tells you which nutrients you are actually getting. Without it, you are buying a category, not a product.

Cultivation method. Closed photobioreactor or open pond? If the product page does not say, ask. We state our method on every product page because we consider it a genuine differentiator, not a marketing flourish. Most reputable producers do the same. Silence on this point is worth noticing.

Quantified nutrients per serving. Check the nutritional information panel for milligrams of the active nutrient per capsule or per scoop. Your body does not respond to adjectives like "omega-3 rich" or "nutrient dense." It responds to milligrams.

If a product does not declare its EPA, DHA, or protein content per dose, you cannot meaningfully compare it to anything else on the shelf. Our guide to reading algae supplement labels covers this in detail.

Common Confusions About Microalgae

Microalgae vs Seaweed: Why the Distinction Matters

We hear this confusion constantly: people use "algae" to mean both microalgae and seaweed. If you have ever stood in a health shop wondering whether a kelp tablet and a chlorella tablet do the same thing, the answer is no. Microalgae are single-celled and grown in controlled systems for specific nutrient targets. Seaweed is multicellular and harvested from the ocean or farmed in coastal waters.

Kelp provides iodine that many UK diets lack. Nori is a culinary staple. But seaweed does not provide meaningful amounts of EPA or DHA, and its protein content is far lower than chlorella's. If you bought a seaweed supplement expecting omega-3, you bought the wrong type of algae.

If someone recommends "algae" for omega-3, they mean microalgae. If they recommend it for iodine, they probably mean seaweed. The supplement shelf groups them together, but your body will notice the difference. For a deeper look, see our article on microalgae vs algae.

Is Spirulina a Microalga?

Spirulina (Arthrospira platensis) is technically a cyanobacterium, not a eukaryotic microalga. It photosynthesises and is cultivated similarly, but its cell structure and biology are different. It is high in protein and phycocyanin (a blue pigment with antioxidant properties) but does not provide EPA or DHA.

The supplement industry markets spirulina alongside chlorella and Nannochloropsis under the broad "algae" umbrella. The nutritional discussion overlaps, but if you have been adding spirulina to your morning porridge thinking it covers your omega-3 intake, it does not. Our guide to the most important types of nutritional algae covers where each one fits.

What Working With Microalgae Commercially Taught Us

We have spent years sourcing, testing, and formulating with multiple microalgae species. Some of what we learned does not appear on product labels or in competitor articles, but it shapes how we think about every product decision we make.

The word "microalgae" on a label tells you almost nothing useful. Species determines your nutrient profile entirely. Chlorella gives you protein and chlorophyll. Nannochloropsis gives you EPA. Schizochytrium gives you DHA. A product labelled "microalgae blend" without naming species is asking you to trust a category that spans hundreds of thousands of organisms.

Marine and freshwater microalgae serve fundamentally different nutritional roles. We work with both. Our marine phytoplankton (Nannochloropsis) is an omega-3 source. Our chlorella is a protein and chlorophyll source grown in freshwater. Treating them as interchangeable would be like treating olive oil and whey protein as the same product because both come from food.

The supplement shelf groups organisms from different biological kingdoms under one label. Spirulina is a cyanobacterium. Chlorella is a eukaryotic green alga. They are as biologically distant as a mushroom and a fern. Yet you will find them side by side in the same aisle, marketed with the same language. When we evaluate raw materials, that taxonomic difference matters for cell structure, digestibility, and nutrient access.

Cultivation method matters more than species marketing. Two chlorella products from different growing systems can differ more in purity than chlorella and Nannochloropsis from the same photobioreactor facility. We learned this by comparing batch test results across suppliers. The growing system is the variable most buyers overlook and most manufacturers understate.

No single microalgae species covers all nutritional bases, which is why multi-species formulations exist. We formulate with more than one species because the gaps are real. Nannochloropsis does not deliver meaningful protein. Chlorella does not deliver meaningful EPA. If a single species did everything, we would use it. The biology does not work that way.

Microalgae FAQ

Are microalgae supplements safe to take?

The microalgae species used in commercial supplements (chlorella, Nannochloropsis, Schizochytrium, Haematococcus, Dunaliella) have established safety records and are approved for sale as food supplements in the UK and EU. Safety depends on cultivation quality and dosage. Buy from manufacturers who publish third-party test results.

If you are pregnant, breastfeeding, or taking anticoagulant medication, check with your GP before starting any microalgae supplement. EPA-containing products in particular may interact with blood-thinning drugs at higher doses.

Can microalgae supplements replace fish oil?

For EPA and DHA specifically, yes. Microalgae are the original source of these omega-3 fatty acids. Algae-derived EPA (from Nannochloropsis) and DHA (from Schizochytrium) deliver the same fatty acids without the fish. Whether a specific algae supplement matches a specific fish oil product depends on the dose per serving, so check the milligrams on the label rather than assuming equivalence.

What is the difference between microalgae and seaweed?

Microalgae are microscopic single-celled organisms. Seaweed (macroalgae) is multicellular and visible. They offer different nutrients: microalgae for omega-3 and concentrated protein, seaweed for iodine and trace minerals. They are not interchangeable in a supplement context.

Why do some labels say "microalgae" without naming the species?

Usually because the product uses a proprietary blend or the manufacturer does not want to disclose the exact composition. This makes it difficult for you to evaluate the product's nutritional value, because different microalgae species contain very different nutrients. A label that names the species is more transparent than one that does not.

Do you need both EPA and DHA from microalgae?

EPA and DHA serve different biological functions. EPA contributes to normal heart function. DHA contributes to normal brain function and normal vision. The EFSA-authorised health claim applies at a combined 250 mg daily.

No single microalgae species provides both in high concentrations. If you want a complete plant-based omega-3 profile, you would typically combine a Nannochloropsis-based product (EPA) with a Schizochytrium-based product (DHA). Our plant-based omega-3 guide covers the options.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your GP before starting any supplement.

Methodology and Disclosure

Phytality manufactures microalgae supplements including marine phytoplankton from Nannochloropsis gaditana (grown in closed photobioreactors) and fermented chlorella. We have a direct commercial interest in several of the species discussed in this article. Taxonomic descriptions reflect established biology. Species-level nutritional claims are drawn from published literature cited above.

The EFSA-authorised health claims for EPA, DHA, and their combined intake are cited under Regulation EU 432/2012 with intake conditions stated. ALA conversion rates are drawn from Brenna et al. (2009). Compositional comparisons between species reflect established differences documented in published reviews (Barkia et al., 2019; Levasseur et al., 2020).

Where we describe our own cultivation method and heavy metal comparisons, this reflects our actual production and formulation process. Label-reading guidance draws on our experience as a manufacturer evaluating ingredient sourcing.

Last reviewed: March 2026. Next review due: March 2027.