What Is Microalgae? A Species-by-Species Guide to Algae Supplements

Microalgae is not one supplement. It is a loose commercial category covering microscopic organisms with radically different biology and nutrition. Chlorella is usually sold as whole-cell biomass, Nannochloropsis for EPA, Schizochytrium oil for DHA, and Haematococcus extract for astaxanthin.

To compare two products properly you need three things: the species, the product form, and how many milligrams of the nutrient you are after arrive in a day. A label that gives you none of those is not describing a product. It is describing a category that spans hundreds of thousands of organisms.

Microalgae Species Compared: What Each One Actually Delivers

Chlorella gives you protein and chlorophyll, Nannochloropsis gives you EPA, and Schizochytrium oil gives you DHA. Haematococcus gives you astaxanthin and very little else, while spirulina, sold alongside all of them, is not an alga at all. What each one fails to provide matters as much as what it does, so the table carries that column too.

Why Microalgae Is Not One Biological Category

"Microalgae" is a practical umbrella term, not a taxonomic rank. There is no microalgae kingdom. The organisms it covers sit in several unrelated lineages, and grouping them reflects how they are grown and sold rather than how they are related.

The standard definition is single-celled, photosynthetic and aquatic. That definition fails on the species most vegan DHA supplements depend on. Schizochytrium is a heterotrophic marine protist. It does not photosynthesise at all, and grows in fermentation tanks on organic carbon. It is grouped with microalgae by commercial convention.

Spirulina fails the definition from the other direction. It is a cyanobacterium, a photosynthetic bacterium with no nucleus, sold beside chlorella and discussed in the same breath. Chlorella and spirulina are about as closely related as you and a mushroom.

This is not pedantry, and it is not only a taxonomy problem. If the category label covers organisms that do not share a definition, it cannot tell you anything reliable about what is in the tub.

What Each Microalgae Species Provides Per Serving

Composition is usually quoted as a percentage of dry weight. That number describes the powder in the tub, not the amount you swallow. Your body does not receive percentages. It receives what is in the scoop or the capsule, so the figure to compare is grams or milligrams per daily serving.

Protein From Microalgae, Converted to Grams

Chlorella is roughly 50 to 60 per cent protein by dry weight, which sounds substantial. At a typical 5 g serving that is about 2.5 to 3 g of protein. Useful, but roughly what you would get from a large egg white, at considerably greater cost.

Nannochloropsis is commonly cited at 30 to 40 per cent protein. Servings are smaller, often 1 to 3 g, which puts the protein contribution under a gram. That is why we describe it as an omega-3 source rather than a protein source. Both figures are accurate. The serving size is what reconciles them.

Omega-3 From Microalgae, and the Conversion Problem

Nannochloropsis supplies EPA and Schizochytrium supplies DHA. Most plant foods give you only ALA, which your body converts to EPA and DHA at rates generally estimated below 5 to 10 per cent, and lower again for DHA (Brenna et al., 2009).

That conversion bottleneck is the entire reason algal omega-3 supplements exist. It is also why a flaxseed oil capsule and an algal EPA capsule are not substitutes, whatever the shelf label groups them under.

The authorised claim for EPA and DHA applies at a combined intake of 250 mg per day. When you compare products, compare that number. Not the total oil weight, and not "omega-3" as an undifferentiated figure, which can be mostly ALA.

Whole-Cell Microalgae Biomass Versus Extracted Oil

The same species reaches you in two quite different products, and the evidence for one does not automatically apply to the other. Which form you are holding changes what comes with the fatty acids, what your digestion has to do, and which studies are relevant to the tub in your hand.

A whole-cell powder gives you the cell intact: fatty acids alongside pigments, protein and micronutrients, with a cell wall your digestion has to get through. An extracted oil gives you concentrated fatty acids, no pigments, and no cell wall to negotiate.

Human trials on algal omega-3 have generally used specific extracts at defined doses. Those results describe the material tested. They do not transfer to every product carrying the same species name, because the form, the dose and the processing all differ. If a whole-cell powder cites a trial run on an extract, that citation is doing more work than it should.

What Microalgae Cultivation Changes, and What It Cannot Prove

Cultivation method affects contamination exposure, batch-to-batch consistency and price. It is a genuine differentiator, and it is also routinely oversold, and we oversell it as readily as anyone else with a closed system to talk about.

Closed Photobioreactors and Open Ponds

A photobioreactor is a sealed vessel where light, temperature and nutrients are controlled. Open-pond cultivation uses shallow outdoor pools, which is cheaper and easier to scale but leaves the biomass exposed to dust, competing organisms, weather and whatever the water carries.

Closed systems reduce exposure and make batches more consistent. What they do not do is guarantee low heavy metals, whatever the marketing implies. Purity is decided by the water source, the nutrient inputs and the testing applied to the finished batch. A sealed tube fed contaminated inputs produces contaminated biomass, so what you want from a seller is the certificate rather than the cultivation adjective.

So treat cultivation method as one input to a purity judgement rather than the answer to it. The document that settles the question is a batch certificate of analysis, not a description of the equipment.

A Five-Point Checklist for Reading a Microalgae Label

Every check below can be confirmed from a label, a product page or a document request. None of them asks you to take a brand's word for anything, including ours.

1. The species, in Latin. Chlorella vulgaris or Nannochloropsis gaditana is a species. "Marine algae blend" is not, and cannot be checked against any published composition figure.
2. The product form. Whole-cell biomass or extracted oil. This determines what else comes with the fatty acids, and which evidence applies.
3. The target nutrient per daily serving. Milligrams of EPA, DHA or protein per capsule or scoop, and the number of capsules that constitutes a serving.
4. A batch certificate of analysis, with reporting limits. "Below detectable levels" means little without the detection limit stated. Ask for the figure and the limit together.
5. The cultivation method, treated as context. Useful to know, but read it alongside the certificate rather than instead of it.

If a brand cannot supply points one to four, you do not have enough information to compare the product with anything else. That is a reason to keep looking, and it applies to us as much as anyone.

What Working With Microalgae Taught Us

We source, test and formulate with more than one microalgae species. Three things follow from that which do not appear on any label.

Species selection came down to where the omega-3 sits chemically, not the headline total. The marine strains we screened carried their omega-3 as EPA directly. The freshwater greens carried theirs as ALA, which then depends on your conversion. A large "total omega-3" figure can be mostly the form that helps least.

No single species covers the ground. Nannochloropsis does not deliver meaningful protein at its serving size. Chlorella does not deliver EPA. If one organism did everything we would use it and save ourselves the complexity.

Cultivation method is necessary and not sufficient. We use closed photobioreactors because contamination exposure matters, but the finished-batch test is what we actually rely on. Any manufacturer who leads with the growing system and goes quiet on batch results has the emphasis the wrong way round.

Limits of the Microalgae Evidence

Four different kinds of evidence get blended together in writing about algae: laboratory composition, absorption data, human trials, and legally authorised claims. They are not equivalent, and a claim that holds under one can fail completely under another.

Laboratory composition tells you what is in the biomass. It says nothing about how much you absorb. Absorption data addresses that, and varies with cell wall processing and product form. Human trials test defined doses of defined materials, and their results belong to the material tested. Authorised claims are a legal category: a regulator has accepted a specific wording at a specific intake.

In Great Britain, only claims listed on the GB Nutrition and Health Claims Register may be used, and that register is now maintained separately from the EU list. A claim being permissible is a statement about regulatory acceptance, not a summary of the whole evidence base.

What is not established: that whole-cell microalgae powders reproduce trial results obtained with extracts, that any microalgae species detoxifies anything, or that broad "superfood" benefits follow from nutrient density measured in a laboratory. We do not make those claims, and you should treat them with suspicion wherever you find them.

Microalgae FAQ

If you read nothing else on this page: compare products on milligrams of EPA or DHA per daily serving, and check that the species is named in Latin. Almost every question we get reduces to one of those two habits.

Are microalgae supplements safe to take?

The species used commercially have established safety records, but regulatory status is not blanket. It depends on the species, the strain, the ingredient form, the intended use and the country. Safety in practice depends on cultivation quality and testing, so buy from manufacturers who publish batch results.

If you are pregnant, breastfeeding, or taking anticoagulant medication, speak to your GP before starting. EPA and DHA at higher doses can affect clotting.

Can microalgae supplements replace fish oil?

For EPA and DHA specifically, yes. They are the same molecules, and microalgae are where fish get them. Whether a given algae product matches a given fish oil depends on milligrams per serving, so compare that figure rather than assuming equivalence.

How do I compare two microalgae products fairly?

Convert both to the target nutrient per daily serving. Multiply the amount per capsule by the number of capsules in a serving, then compare like with like. Percentages of dry weight and total oil weight are not comparable figures.

Is spirulina a microalga?

Not strictly. Spirulina is a cyanobacterium, which is a bacterium that photosynthesises. It is high in protein and phycocyanin, gives you no EPA or DHA at all, and its B12 is largely pseudovitamin B12, which is inactive in humans and will not count towards your intake.

What is the difference between microalgae and seaweed?

Microalgae are microscopic and single-celled. Seaweed is multicellular and visible. Seaweed is a useful iodine source; it does not supply meaningful EPA or DHA. They are not interchangeable, despite sharing a shelf.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your GP or a qualified healthcare professional 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 species discussed here, and this article links to our products. It should be read as material connected with the supply of those products.

Taxonomic statements reflect established biology, including the classification of Schizochytrium as a heterotrophic protist and spirulina as a cyanobacterium. Compositional ranges are drawn from the published reviews cited above. Per-serving figures are arithmetic applied to those ranges at stated typical serving sizes, and are illustrative rather than product specifications. ALA conversion figures are from Brenna et al. (2009).

Health claims for EPA and DHA are cited with their intake condition. In Great Britain only claims on the GB Nutrition and Health Claims Register may be used. Descriptions of our own cultivation and species selection reflect our formulation process. Quantified batch and testing data are not published in this article; where we describe our testing, we are describing process rather than results.

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