Common eelgrass

Common Eelgrass (Zostera marina L.): A Comprehensive Reference

1. Identity, Taxonomy, and Natural Source

Botanical name: Zostera marina L. (Linnaeus, 1753). The accepted family is Zosteraceae. Zostera marina, or common eelgrass, belongs to the family Zosteraceae, one of the four Alismatales families (basal monocots) that make up the seagrasses. Common synonyms include Zostera maritima Gaertn. and Zostera stenophylla Raf.

Common names: Zostera marina is a species of seagrass known by the common names common eelgrass and seawrack. The name "seawrack" refers specifically to detached plants carried ashore by ocean currents.

Taxonomic and evolutionary context: The common eelgrass Zostera marina is a marine flowering plant which, similar to all seagrasses, evolved from land plants but returned to the sea about 140 million years ago.

Distribution and habitat: This species is known primarily by the English name of eelgrass and is a saline soft-sediment submerged plant native to marine environments on the coastlines of northern latitudes from subtropical to subpolar regions of North America and Eurasia. It is the most wide-ranging marine flowering plant in the Northern Hemisphere. It lives in cooler ocean waters in the North Atlantic and North Pacific, and in the warmer southern parts of its range it dies off during warmer seasons. It grows in the Arctic region and endures several months of ice cover per year. Today, eelgrass meadows dominate the soft sediment shorelines of the temperate northern hemisphere, including Atlantic and Pacific Oceans. Due to its high tolerance to low and variable salinity levels, Z. marina represents the most common seagrass in the brackish Baltic Sea.

Morphology: Zostera marina is a perennial plant growing from a thick, creeping underground stem (rhizome), 2 to 5 cm long, with many roots and nodes spaced 10 to 35 mm apart. Alternate ribbon-like leaves with rounded tips arise from these nodes. The plant is monoecious, with an individual bearing both male and female flowers in separate alternating clusters. The inflorescence is about 10 cm long. The fruit is a nutlet with a transparent coat containing the seed.

Commercial and supplement forms: As a natural ingredient and dietary supplement, Z. marina is sourced in several forms:

• Dried whole plant or leaf powder: Produced from dried leaves, stems, and/or rhizomes, ground for use in encapsulated supplements or bulk powders.
• Isolated pectin (zosterin): Zosterin, from a chemical point of view, is a polysaccharide of pectin nature. It is a highly active polyanionic adsorbent.
• Standardized extracts: Studies on the components of Z. marina extracts have led to the isolation and identification of various metabolites with significant bioactive properties. An interesting study using supercritical CO₂ extraction followed by mass spectrometric characterization showed the presence of 77 different biologically active components in Z. marina, 53 of which were polyphenols.
• Topical/cosmetic extracts: Used in serums, creams, and masks for skin-care applications.
• Whole-grain/flour food preparation: The eelgrass grain is harvested in spring and has historically been processed into flour, described further in the Traditional Use section below.

2. Traditional and Historical Use

2.1 The Seri (Comcaac) People of Mexico — Food Use

Zostera marina occurs in the northern Gulf of California. The grain of eelgrass is harvested in the spring and formed an important part of traditional Seri diet and culture. This is the only known case of a grain from the sea being used as a human food source.

Since ancient times, the Seri people of present-day Mexico have known the nutritional quality of the seeds of Z. marina, which they used to bake their daily bread. The native Seri or Comcaac people named the month of April "moon, when the seeds of marine wheat ripen." The sandmen, who lived near the Cortés coast and in the eastern foothills of the Sonora desert, dried out the plants and shook them to harvest the grain. Memoirs written by the explorer Álvar Núñez Cabeza de Vaca in the 16th century confirm that flour acquired from the fruit of this aquatic plant played an important role in the traditional diet of the indigenous tribe. It was used for making cakes and hot drinks (atoles).

Known as xnois, this grain from the Zostera marina seagrass was once a vital ingredient in Comcaac food, and was sustainably harvested without harming seagrass meadows. Current generations of Comcaac hope to revive the ancient traditions while preserving the seagrass meadows off the coast of their territory. Through a recent cultural festival, they showcase the versatility of xnois in both traditional and modern cuisine, from tortillas to energy bars.

The Seri hunter-gatherers of Mexico eat eelgrass grains after toasting them and grinding into a paste. As reported by Felger and Moser in a landmark 1973 article in Science, this grinding and toasting of the grain is unique in the ethnobotanical record as the sole instance of a maritime grass grain forming a dietary staple.

2.2 Northwest Coast Indigenous Peoples of Canada — Food Use

Eelgrass (Zostera marina, L.; Zosteraceae) was one of the species managed by Indigenous Peoples of the Northwest Coast Cultural Area of North America. The Kwakwaka'wakw harvested its sweet rhizomes in the springtime. The Seri Indians harvested Z. marina to produce flour from seeds or in the southwest coast of Canada where the Kwakwaka'wakw harvested rhizomes of Zostera marina in spring for food. The Kwak'wala word for Zostera marina (eelgrass) is ts'áts'ayem (pronounced ts'AH-ts'AH-yem).

2.3 Scandinavia and Northern Europe — Agricultural, Domestic, and Industrial Use

People have long used this plant species as roof thatching in some areas. On Læsø in Denmark, a tradition of using eelgrass as roof material is recognised by being included on the Tentative List of World Heritage Sites since 2023. It has been used as fertilizer and cattle fodder in Norway for centuries. It has also been dried and used as stuffing for mattresses and furniture.

Wild gathering of the leaves of the submerged marine monocotyledon Zostera marina L. once formed the basis of a vigorous insulation industry in North America. Since European colonization, fishing communities used detached leaves, deposited on the beach by tide and wind, as green manure and domestic insulation, but beginning in the late 1800s, these leaves were utilized in a commercial insulating product. Two companies manufactured seagrass "quilts" that were installed in many buildings of the period including some of the first skyscrapers.

2.4 Modern Culinary Revival

Ángel León, a Spanish chef, has planted meadows of Z. marina (described as "sea rice") in the Bay of Cádiz in order to harvest the grains. This modern culinary project draws explicitly on the nutritional tradition documented in the Seri ethnobotanical record.

3. Key Constituents and Active Compounds

Zostera marina produces a diverse and chemically distinctive array of bioactive molecules, shaped by its adaptation to marine environments. The main compound classes documented in peer-reviewed literature are summarized below.

3.1 Zosterin (Apiogalacturonan Pectin)

The plant produces a special pectin which has no analogues in other plants. It was first isolated in 1940 by the Russian scientist V.I. Miroshnikov, who named it zosterin. Zosterin, from a chemical point of view, is a polysaccharide of pectin nature.

The pectin from Zostera marina has unique features that distinguish it from the glycans of other land plants. Numerous studies have shown that zosterin has a more complex structure than land plant pectins. Although it, like other pectins, has a linear backbone of rhamnogalacturonan and a branched region, however, the latter is a much more complex configuration. Another "block" is attached to it — xylogalacturonan (chains consisting of rings of galacturonic acid and xylose).

Zosterin, an apiose-rich pectic polysaccharide, was extracted and purified from the sea grass Zostera marina. Structural studies by gas chromatography and NMR spectroscopy on a purified zosterin fraction revealed a typical apiogalacturonan structure comprising an alpha-1,4-D-galactopyranosyluronan backbone substituted by 1,2-linked apiofuranose oligosaccharides and single apiose residues. The average molecular mass was estimated to be about 4,100 Da with a low polydispersity.

As a highly active polyanionic adsorbent, zosterin passes through the gastrointestinal tract, binds and removes heavy metal ions, bile acids, pathogenic microorganisms, and similar substances from the body. Research has shown that these pectins are among the most complex in structure of objects of natural origin, and this unique feature gives them a high adsorption capacity. Because of this, a pectin called zosterin has found extensive use in medicine.

3.2 Zosteric Acid

Zosteric acid, a sulfated phenolic acid, has been uniquely associated with Zostera species. Zosteric acid (ZA), a sulfated phenolic acid only seen in Zostera species, has been found to prevent the settlement of marine bacteria, algae, barnacles and tubeworms. Zosteric acid is reported not only to be effective in combating biofouling but also to be environmentally safe. Zosteric acid occurs naturally in eelgrass Zostera marina.

3.3 Rosmarinic Acid and Phenolic Acids

A prominent component within Zostera species is rosmarinic acid, characterized as a bioactive dimeric phenylpropanoic acid. Rosmarinic acid (RA), widely known for its biological activities, including antioxidant and antifouling action, has been identified as one of the major compounds in Z. marina.

Among simple phenolic acids, gallic, caffeic, p-coumaric, protocatechuic, and ferulic acids have been identified in Zostera species. They also contain large quantities of phenolic acids such as p-coumaric acid, vanillin, ferulic acid, gentisic acid, and chicoric acid, along with significant concentrations of catechins.

3.4 Flavonoids

Flavonoids, constituting the second major class of phenolics in the genus Zostera, exhibit sulfate moieties commonly found in marine-derived flavonoids. Three compounds isolated from an ethyl acetate-soluble fraction of Z. marina were identified as apigenin-7-O-beta-D-glucoside, chrysoeriol, and luteolin.

A 2024 phytochemical study (Fitoterapia) of Z. marina MeOH extract isolated and identified ten compounds: caffeic acid (1), 3,4-dihydroxybenzoic acid (protocatechuic acid) (2), luteolin (3), diosmetin (4), 4-coumaroyl-4′-hydroxyl phenyllactic acid (5), rosmarinic acid (6), caffeoyl-4′-hydroxy-phenyllactic acid (isorinic acid) (7), apigenin 7-O-β-D-glucopyranoside (8), luteolin 7-O-β-D-glucopyranoside (9), and luteolin 7-sulfate (10).

Studies on the components of Z. marina extracts have led to the isolation and identification of various metabolites with significant bioactive properties, highlighting unsaturated fatty acids, phenolic compounds such as rosmarinic acid, luteolin, sagerinic acid, umbelliferone and pectins, particularly zosterin.

3.5 Sulfated Polyphenols and Other Compounds

Z. marina contains various phenolic compounds and sulfated polyphenols with valuable biological activity. The phenolic metabolites detected in Z. marina that have been implicated in its defense include flavonoids in sulfated and unsulfated form, as well as acids like caffeic, p-coumaric, ferulic, and zosteric, and rosmarinic acids, all of which are hydroxy, sulfoxy, or ester forms of cinnamic acid.

Tandem mass-spectrometry (HPLC-ESI-ion trap) was applied to detect target analytes, and 77 different biologically active components have been identified in Z. marina supercritical CO₂-extracts.

4. Mechanisms of Action

4.1 Adsorption and Heavy Metal Chelation (Zosterin)

As a highly active polyanionic adsorbent, zosterin passes through the gastrointestinal tract and binds and removes heavy metal ions, bile acids, and pathogenic microorganisms from the body. The leaves of Z. marina synthesize the polysaccharide zosterin, which is a natural ligand for heavy metals. The high adsorption capacity derives from zosterin's unique branched apiogalacturonan structure, which provides abundant carboxylate and hydroxyl groups capable of forming coordination complexes with divalent and trivalent metal ions.

4.2 Free Radical Scavenging and Antioxidant Activity

The isolated flavonoids apigenin-7-O-beta-D-glucoside, chrysoeriol, and luteolin were found to scavenge radicals and reactive oxygen species (ROS), measured with SC₅₀ values of 0.18 mM, 0.68 mM, and 0.01 mM against the DPPH radical and 0.04 mM, 0.03 mM, and 0.01 mM against the superoxide radical in the xanthine/xanthine oxidase system, respectively.

Eelgrass has a robust defense system which includes surface-associated metabolites like fatty acids and phenolics, p-coumaric acid, rosmarinic acid, and zosteric acid. These compounds play wide-ranging roles including signaling, antioxidant activity, free radical scavenging activity, and regulation of auxin transport.

4.3 Inhibition of Matrix Metalloproteinases and Pro-inflammatory Cytokines

Luteolin suppressed the expression of MMP-1 by up to 44% at 4.0 μM and inhibited the production of interleukin 6 (IL-6), which is known as a cytokine that induces MMP-1 expression. Matrix metalloproteinase-1 (MMP-1) is a key mediator of collagen degradation in skin photoaging, making MMP-1 inhibition a mechanistically important activity for anti-aging applications.

4.4 Immunomodulation

There is a wide array of potential activities reported for zosterin fractions, such as stimulation of protein production in hepatocytes, inhibition of neutrophil adhesion, gastroprotective effects, and a general immunomodulatory effect.

4.5 Gastroprotection

Data obtained from preclinical studies demonstrate that zosterin enhances resistance of the stomach tissue to various ulcerogenic factors (emotional stress, indomethacin, pesticide 2,4-D). It was shown to possess a gastroprotective effect, which is accompanied by diminution of the number and sizes of destructive regions in the gastric mucosa during ulcer affection, as well as reduction of ATP and glycogen deficit, decrease of lactate excess, and normalization of the energy balance in the gastric mucosa.

4.6 Antifouling Activity of Zosteric Acid

Zosteric acid prevents the attachment of organisms to a surface without necessarily being toxic towards the organism. For example, in a barnacle attachment assay, barnacles stopped swimming when exposed to the active agent but quickly recovered when transferred to clean seawater, suggesting that attachment was prevented by a mechanism other than acute toxicity.

5. Scientific Evidence by Area of Use

5.1 Antioxidant and Photoprotective Activity

Several in vitro studies have characterized the antioxidant potential of Z. marina extracts and isolated compounds.

Methanol crude extract of Z. marina and organic solvent fractions (n-hexane, chloroform, ethyl acetate, n-butanol, and water) were screened for antioxidant activity, including total phenolic contents, DPPH scavenging activity, and reducing power. Total phenolic contents and DPPH scavenging activity were highest in the ethyl acetate fraction, with approximately 95% scavenging activity on DPPH radicals at 10 mg/mL.

A study published in Fitoterapia (2024) examined anti-photoaging potential: A methanolic extract of Z. marina showed anti-phototoxicity and anti-melanogenesis activity with an IC₅₀ of 17.5 μM. The isolated compounds were found to exhibit good anti-phototoxicity and anti-melanogenesis activities by increasing the viability of UVB-irradiated HaCaT cells by 6% to 34% and by inhibiting melanin synthesis in B16 melanoma cells by 44% to 65%.

A PubMed-indexed study (2004) on anti-photoaging specifically isolated luteolin and two other flavonoids: In order to develop new anti-photoaging agents, researchers examined the antioxidative activity and the inhibition effect of matrix metalloproteinase-1 (MMP-1) on extracts of Zostera marina L. Three compounds were isolated from an ethyl acetate-soluble fraction, identified as apigenin-7-O-beta-D-glucoside, chrysoeriol, and luteolin.

Evidence strength: All antioxidant and photoprotective evidence is currently limited to in vitro (cell culture) and bench-chemistry studies. No human clinical trials have been published on these endpoints for Z. marina specifically.

5.2 Antimicrobial Activity

In antimicrobial activity tests, minimum inhibitory concentrations (MICs) of each Zostera marina extract fraction ranged from 1 mg to 8 mg (extract/10% DMSO) against all three human skin pathogens tested: Staphylococcus aureus, Staphylococcus epidermidis, and Candida albicans.

Antibacterial bioassay showed that the n-butanol fraction was effective only for Staphylococcus aureus, the petroleum ether fraction was effective for S. aureus and Bacillus anthracis, and the ethyl acetate fraction was effective for S. aureus, B. anthracis, Diphtheroid bacilli, and Staphylococcus epidermidis, while the water fraction had no effect.

Rosmarinic acid isolated from eelgrass has also been documented as nematicidal and antibacterial: Rosmarinic acid from eelgrass shows nematicidal and antibacterial activities against pine wood nematode and its carrying bacteria. Extracts of Zostera marina showed a high nematicidal activity against pine wood nematode (PWN) and some of the bacteria that it carries.

Evidence strength: All antimicrobial data are from in vitro bioassay experiments. No clinical trials in humans have evaluated antimicrobial efficacy of Z. marina preparations.

5.3 Anti-inflammatory Activity

A 2025 review published in Marine Drugs (MDPI, PMC-indexed) examined Mediterranean seagrasses including Z. marina: This review provides current knowledge of the potential benefits of native Mediterranean seagrasses for human health, specifically focusing on their anti-inflammatory and antioxidant properties. The four main species examined — Posidonia oceanica, Cymodocea nodosa, Zostera marina, and Zostera noltii — are integral components of marine ecosystems, providing essential habitats and supporting biodiversity. Recent studies highlight their rich bioactive compounds that show significant therapeutic potential against oxidative stress and chronic inflammation, which are prevalent in various health disorders.

Compounds such as polysaccharides or secondary metabolites such as polyphenols and flavonoids produced by marine plants exhibit a broad range of beneficial properties, including anti-inflammatory, antibacterial, antioxidant, and antidiabetic qualities.

Luteolin, one of the primary flavonoids in Z. marina, suppressed IL-6 production in vitro, as described in the Mechanisms section above. IL-6 is a key pro-inflammatory cytokine; its inhibition is considered a relevant mechanistic indicator of anti-inflammatory potential.

Evidence strength: Evidence is in vitro and review-level; no controlled human clinical trials have been conducted on anti-inflammatory outcomes from Z. marina supplementation.

5.4 Heavy Metal Adsorption and Toxin Binding (Zosterin)

Zosterin's role as a heavy metal chelator has been investigated primarily through Russian biochemical research originating with Ovodov and colleagues, and subsequently in applied chemistry studies.

The use of zosterin as a dietary supplement has an antiulcer effect, normalizes the function of the gastrointestinal tract, enhances the feeling of satiety, thereby facilitating the tolerance of low-calorie diets.

Zosterin, bioactive pectin from the eelgrass Z. asiatica, decreases the toxicity of antitumor drugs and purges heavy metals from human organisms. This claim, attributed to preclinical and early clinical-stage work originating in Russia and the former Soviet Union, has been referenced in peer-reviewed chemical literature but lacks large-scale, independently replicated randomized controlled trial data.

Antioxidant, antitumor, and chelating effects were discovered, and biological properties of pectins — in particular, their binding activity — are strictly dependent on the degree of esterification.

Evidence strength: Heavy metal chelation by zosterin has been investigated in preclinical models and in early-stage human work from Russian research groups. The body of evidence lacks large, independently replicated human trials and has not been evaluated by major regulatory bodies such as the NIH Office of Dietary Supplements or EFSA in formal safety/efficacy assessments. The mechanistic plausibility (polyanionic adsorption of cationic metals) is chemically sound.

5.5 Gastroprotective Effects (Zosterin)

Preclinical rat studies evaluated zosterin's gastric protective properties: Zosterin was given to rats intragastrically once 1 hour before emotional stress or injection of indomethacin, or administration of 2,4-D solution daily for seven days at a dose of 100 mg/kg. The data obtained demonstrate that zosterin enhances resistance of the stomach tissue to various ulcerogenic factors. It was shown to possess a gastroprotective effect, accompanied by diminution of the number and sizes of destructive regions in the gastric mucosa during ulcer affection, as well as reduction of ATP and glycogen deficit, decrease of lactate excess, and normalization of the energy balance in the gastric mucosa.

Evidence strength: Preclinical (animal, rodent) only. No human gastroenterological clinical trials have been identified for zosterin specifically derived from Z. marina.

5.6 Potential Antitumor and Antiproliferative Activity

Of exceptional interest are experimental data on the antitumor properties of zosterin and its ability to prolong life, i.e., act as a potential geroprotector.

A structural characterization study reported that a purified zosterin fraction (AGU): inhibited proliferation of A431 human epidermoid carcinoma cells with an approximate IC₅₀ value of 3 μg/mL (0.7 μM). In addition, AGU inhibited A431 cell migration and invasion.

A related finding was reported for a phenolic compound zosterabisphenone B: Z. marina showed selective cytotoxic effects on HCT116 tumour cells with IC₅₀ of 3.6 μM at 48 h. Zosterabisphenone B induced apoptosis in HCT116 colon cancer cells, increasing the levels of cleaved caspases, PARP, and BH3 Interacting Domain Death Agonist.

Evidence strength: Entirely in vitro (cell culture). No human oncology trials have been performed. These findings are preliminary and cannot be extrapolated to clinical efficacy claims.

5.7 Metabolic (Antidiabetic and Lipid) Effects

The therapeutic effect of rosmarinic acid, luteolin and its sulfated derivatives — among the most active components of Z. marina — are considered in detail in experimental studies in diseases associated with impaired carbohydrate and lipid metabolism. The properties of zosterin's pectins allow the use of zosterin in diabetes mellitus as an auxiliary antidiabetic agent.

Evidence strength: Preliminary and experimental. The mechanistic basis involves pectins' known capacity to slow glucose absorption and modulate bile acid recirculation — mechanisms shared with dietary fiber generally. No clinical trials specific to Z. marina and glycemic control have been identified in the peer-reviewed literature.

5.8 Algicidal (Anti-HAB) Activity

The inhibitory effects of crude extracts of Zostera marina L. and Zostera noltii on the growth of the toxic red tide dinoflagellate Alexandrium catenella were investigated through bioassays. Methanolic and aqueous extracts were prepared from fresh and detrital leaves collected in the Thau lagoon and Arcachon bay (France). All the extracts exhibited significant inhibition of A. catenella growth. The effective concentrations (EC₅₀) varied in the range 0.036–0.239 g/L for Z. marina. Results showed the predominance of flavonoids and phenolic acids. Total phenolic concentrations correlated negatively with the EC₅₀ values, suggesting that these secondary metabolites might be responsible for the observed algicidal effects.

Evidence strength: In vitro bioassay data, ecologically relevant but not directly applicable to human supplementation.

6. Body Systems and Health Areas Associated with Common Eelgrass

• Gastrointestinal system: Zosterin acts as a dietary fiber-type adsorbent in the GI tract, with documented preclinical gastroprotective, anti-ulcer, and satiety-enhancing properties.
• Detoxification/excretion: Zosterin's polyanionic structure enables binding and facilitated fecal excretion of heavy metal ions, bile acids, and potentially pathogenic microorganisms in preclinical models.
• Skin and integument: Phenolic compounds (luteolin, rosmarinic acid, caffeic acid) have demonstrated in vitro antioxidant, MMP-1 inhibitory, anti-phototoxic, and melanogenesis-inhibiting activities relevant to photoaging and pigmentation.
• Immune system: Zosterin fractions have shown immunomodulatory effects in experimental models, including stimulation of hepatocyte protein production and inhibition of neutrophil adhesion.
• Metabolic system: Pectin-type dietary fiber constituents are associated in preliminary research with auxiliary antidiabetic and lipid-modulating roles.
• Oncology (experimental only): In vitro antiproliferative and pro-apoptotic activities have been reported for zosterin fractions and phenolic isolates against human carcinoma cell lines.

7. Dosage Forms and Dosages Reported in Studies

Dosage information for Z. marina-derived preparations is sparse, largely preclinical, and not standardized. The following represents dosages as reported in the specific sources identified:

• Gastroprotection (animal, zosterin): Zosterin was given to rats intragastrically once 1 hour before the ulcerogenic challenge at a dose of 100 mg/kg body weight.
• In vitro antioxidant (DPPH assay): DPPH scavenging activity was highest in the ethyl acetate fraction, with approximately 95% scavenging activity at 10 mg/mL.
• In vitro anti-melanogenesis (whole extract): A methanolic extract of Z. marina showed anti-melanogenesis activity with an IC₅₀ of 17.5 μM.
• In vitro antiproliferative (cancer cells, zosterin fraction AGU): AGU inhibited proliferation of A431 human epidermoid carcinoma cells with an approximate IC₅₀ value of 3 μg/mL (0.7 μM).
• In vitro MMP-1 inhibition (luteolin): Luteolin suppressed the expression of MMP-1 by up to 44% at 4.0 μM.

No standardized human clinical dosage for Z. marina dietary supplementation has been established or endorsed by any government body, pharmacopoeia, or major evidence synthesis organization as of the most recent available literature. Zosterin is referenced in Russian medical literature as a pharmaceutical-grade dietary supplement, but specific validated human dosing regimens for Z. marina-derived zosterin are not confirmed by independently replicated large trials.

8. Safety Considerations

8.1 Environmental Contamination Risk

Zostera marina shoots were transplanted in two polluted bay systems on Korean coasts to evaluate heavy metal contaminations in sediments and the possibility of using Z. marina transplants as a bioindicator and phytoremediation agent. Although seagrasses can incorporate heavy metals from the marine environment, few studies have been conducted on heavy metal uptake and phytoremediation potential by seagrass transplants in heavy metal-contaminated sediments. The major concentrated metals in sediments were As, Cu, Fe, and Pb in Jaran Bay, and Cd, Co, Zn, and Hg in Onsan Bay. The Co, Zn, Pb, and Hg concentrations in Z. marina tissues reflected the sediment heavy metal concentrations, and the tissue heavy metal concentrations may be used as bio-indicators of metal contamination. Since Z. marina transplants accumulated a great amount of heavy metals in their tissues, they may have phytoremediation potential for heavy metal-contaminated sediments.

This capacity for heavy metal bioaccumulation in tissues represents a direct and source-specific safety concern for any Z. marina intended for dietary use: plant material harvested from contaminated coastal environments could carry elevated concentrations of arsenic, lead, cadmium, mercury, or other metals. Quality sourcing and testing of raw material origin are therefore critical considerations for supplement production.

8.2 Zosterin and Gastrointestinal Tolerance

The use of zosterin as a dietary supplement has an antiulcer effect and normalizes the function of the gastrointestinal tract. As a soluble fiber-type pectin, zosterin is generally expected to be tolerated similarly to other dietary pectins, though high-dose GI effects (such as flatulence or loose stools) common to soluble fibers cannot be excluded. No formal human safety trial for Z. marina-derived zosterin has been identified in the databases reviewed.

8.3 Anticoagulant Activity — Methodological Note

A described anticoagulant activity should be seen as artificial, because the experiments were performed with sulfated pectic fractions. Researchers reviewing the zosterin literature have flagged that anticoagulant findings may reflect the properties of experimentally sulfated pectin derivatives rather than native zosterin; this distinction is important for interpreting safety-relevant data.

8.4 Absence of Regulatory Classification

Zostera marina and its derived fractions (zosterin, whole-plant extract) do not appear in current monographs of the WHO, ESCOP, European Pharmacopoeia, German Commission E, or the USP. The NIH Office of Dietary Supplements and NCCIH have not issued formal evidence-based monographs or position statements on Z. marina as a dietary supplement ingredient. It therefore lacks the regulatory validation associated with more established botanicals.

8.5 Potential for Seasonal Chemical Variability

Phenolic chemistry in Zostera marina samples was analyzed against latitude, sea depth, sample position within a seagrass meadow, and wave exposure. Multivariate data analysis showed that rosmarinic acid correlated moderately positively with depth, while the flavonoids had an overall strong negative correlation with increasing depth. A higher flavonoid/rosmarinic acid ratio was seen in the periphery of a seagrass meadow, while the contrary ratio was seen in the center. This documented environmental variation in phytochemical composition means that the bioactive profile of supplement material can vary substantially depending on harvest location, season, and depth — a significant quality-control challenge with no resolved standardization protocol in the published literature.

9. Summary Assessment of Evidence Quality

The scientific literature on Zostera marina as a bioactive supplement ingredient is characterized by a strong foundation in phytochemical characterization, a growing body of in vitro bioassay evidence for antioxidant, antimicrobial, anti-inflammatory, gastroprotective, and heavy-metal-chelating activities, and a near-total absence of published human clinical trials. The most developed area — zosterin's use as a dietary supplement for heavy metal detoxification and gastrointestinal normalization — draws on Russian preclinical and early applied medical research that has not been fully replicated in large, placebo-controlled, independently conducted human trials or reviewed by major Western regulatory bodies. All claims of clinical benefit for Z. marina supplement preparations should be understood as preliminary and currently unsupported by high-quality clinical evidence per standard evidence-grading frameworks (e.g., GRADE).

References

• Zhukova et al. (2022). Zostera marina L.: Supercritical CO₂-Extraction and Mass Spectrometric Characterization of Chemical Constituents Recovered from Seagrass. Separations, 9(7), 182. MDPI.
• Wikipedia: Zostera marina — Taxonomy, Distribution, Traditional Uses.
• Seo et al. (2024). Anti-phototoxicity and anti-melanogenesis activities of eelgrass Zostera marina and its phenolic constituents. Fitoterapia. ScienceDirect.
• Overy et al. (2019). Rapid Metabolome and Bioactivity Profiling of Fungi Associated with the Leaf and Rhizosphere of the Baltic Seagrass Zostera marina. PMC/MDPI.
• Vasarri et al. (2025). Potential Use of Marine Plants as a Source of Bioactive Compounds. Molecules, 30(3), 485.
• Felger, R.S. & Moser, M.B. (1973). Eelgrass (Zostera marina L.) in the Gulf of California: Discovery of Its Nutritional Value by the Seri Indians. Science, 181(4097), 355–356. (ResearchGate abstract)
• Felger, R.S. & Moser, M.B. (1973). Eelgrass in the Gulf of California. Science, 181(4097), 355–356.
• Cullis-Suzuki et al. (2015). Tending the meadows of the sea: A disturbance experiment based on traditional indigenous harvesting of Zostera marina L. (Zosteraceae) the southern region of Canada's west coast. Aquatic Botany. ScienceDirect.
• Burdick & Kendrick (2001). The seagrass (Zostera marina) industry of Nova Scotia (1907–1960). Economic Botany. Springer.
• Tae-Hyun, et al. (2004). Antioxidants and inhibitor of matrix metalloproteinase-1 expression from leaves of Zostera marina L. PubMed.
• Mæhre et al. (2021). Variation in Phenolic Chemistry in Zostera marina Seagrass along Environmental Gradients. PMC.
• Khasina et al. (2004). Gastroprotective effect of zosterin, a pectin from seagrass Zostera marina L. ResearchGate.
• Khozhaenko et al. Metal binding activity of pectin isolated from seagrass Zostera marina and its derivatives. ResearchGate.
• Accoroni et al. (2013). Algicidal effects of Zostera marina L. and Zostera noltii extracts on Alexandrium catenella. Aquatic Botany. ScienceDirect.
• Papazian et al. (2019). Surface chemical defence of the eelgrass Zostera marina against microbial foulers. Scientific Reports.
• Lee et al. (2019). Heavy metal accumulation and phytoremediation potential by transplants of the seagrass Zostera marina in the polluted bay systems. PubMed.
• Vasarri et al. (2025). Antioxidant and Anti-Inflammatory Properties of Four Native Mediterranean Seagrasses: A Review. PMC/MDPI Marine Drugs.
• Mongabay (2023). Indigenous Comcaac serve up an oceanic grain to preserve seagrass meadows.
• Frontiers in Marine Science (2023). Characterizing host-pathogen interactions between Zostera marina and Labyrinthula zosterae.
• Isolation and development of rosmarinic acid derivatives from Zostera marina L. and evaluating their hypopigmentation activity. Journal of Biologically Active Products from Nature (2024).