Microalgae vs Algae: What Is the Difference?
"Algae" and "microalgae" are used interchangeably on supplement labels, in marketing copy, and across wellness content. They are not the same thing. Algae is a broad, informal category that includes everything from microscopic single-celled organisms to giant kelp forests.
Microalgae are the microscopic subset: single-celled, photosynthetic, and typically measured in micrometres. If you are buying an algae supplement, knowing which level of the category you are dealing with helps you evaluate what you are actually getting.
What "Algae" Covers
The word "algae" has no precise taxonomic definition. It is a convenience term used in everyday language and in supplement marketing to describe a wide range of photosynthetic organisms that live in water. This includes:
- Microalgae: Single-celled organisms like marine phytoplankton (Nannochloropsis), chlorella, and Schizochytrium
- Macroalgae (seaweed): Multicellular organisms like kelp, nori, dulse, and wakame
- Cyanobacteria: Prokaryotic organisms like spirulina that are photosynthetic but technically bacteria, not true algae
When a supplement says "algae-derived omega-3," it almost always means microalgae. When a food product says "seaweed," it means macroalgae. When a label says "blue-green algae," it usually means spirulina, which is a cyanobacterium. The umbrella term hides these distinctions, which is why we specify species names on our products.
Category labels are not dishonest. They are easier to navigate at the till, and some well-made products use them. But they do not tell you which organism is in the capsule.
Why the Distinction Matters for Supplements
The nutrient profiles of microalgae and macroalgae are fundamentally different. Macroalgae (seaweed) are valued for iodine, minerals, and dietary fibre. They do not contain meaningful amounts of EPA or DHA. Microalgae are the organisms that produce these long-chain omega-3 fatty acids, which is why they are the basis of plant-based omega-3 supplements.
If you see "algae" on a product without further specification, you cannot determine whether it contains microalgae (potentially providing EPA or DHA), macroalgae (providing iodine and minerals), or a cyanobacterium (providing protein and phycocyanin).
We set species-level disclosure as our standard when we first formulated to an EPA target. Without a named species, a fatty acid specification has nothing to anchor to. Species names like Nannochloropsis gaditana are not easy to recognise without background reading, and that learning curve explains why category terms still dominate on shelves. But a species name gives you something to verify. A category label gives you nothing to check.
The Cyanobacteria Complication
Spirulina (Arthrospira platensis) is sold as an algae supplement on most health shop shelves, but it is not an alga. It is a cyanobacterium: prokaryotic, no defined nucleus, different cell architecture from every true microalgae species in your supplement aisle. The nutrient differences follow from that. We cover them in detail in our chlorella vs spirulina comparison.
This is not a reason to avoid spirulina. It is a reason to be precise about what you are buying. "Algae supplement" that turns out to be spirulina is a different product from "algae supplement" that turns out to be Nannochloropsis. The category label tells you almost nothing. The species tells you almost everything.
What our research found
The scale difference is staggering. Roughly 50,000 microalgae species have been described, with estimates up to 200,000 total. Macroalgae number about 10,500 species. Yet only five to seven microalgae species are commercially cultivated for supplements. The term "algae" on a label could refer to any organism across this entire range.
The iodine gap is a hundred-fold. Published data puts macroalgae iodine content at 1,925 mg/kg on average, compared to 17.6 mg/kg for microalgae. If you are concerned about thyroid-affecting iodine from an algae supplement, the relevant question is whether it contains seaweed or microalgae. Chlorella and Nannochloropsis present no meaningful iodine risk at standard doses.
Species-level naming became non-negotiable when we set our EPA specification. When we established the EPA target for our phytoplankton, the species declaration had to come first. You cannot set a fatty acid specification without anchoring it to a named organism. If a product carries no species name, there is nothing for a CoA to verify against. That is why we wrote species disclosure into our product specification from the start.
Sources
- Watanabe F et al. Pseudovitamin B12 is the predominant cobamide of an algal health food, spirulina tablets. J Agric Food Chem. 1999;47(11):4736-4741. PubMed
- Khan MI et al. Microalgae: A multifunctional dietary supplement with diverse medicinal properties. Front Biosci. 2016;21(7):1389-1407. PubMed
- Barkia I et al. Microalgae for High-Value Products Towards Human Health and Nutrition. Mar Drugs. 2019;17(5):304. PubMed
Cara Hayes, MSc Nutrition and Dietetics (University of Sydney), writes all content in the Phytality Knowledge Centre. Read our editorial policy.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your healthcare provider before starting any supplement.
Methodology and Disclosure
Phytality manufactures supplements from microalgae species. We have a commercial interest in the microalgae category being distinguished from broader "algae" marketing. Taxonomic distinctions reflect established biology and phycology. No EFSA-authorised health claims are cited in this article. Our position on species-level labelling derives from our formulation and testing practice, not editorial preference.
Last reviewed: March 2026
