The study, led by Dishti Dabeedass of the University of Mauritius together with colleagues at Hokkaido University in Japan and Jeju National University in the Republic of Korea, focused on the floating-cage facility at Pointe-aux-Feuilles, operational since 2002 and producing roughly 3,000 tons of fish annually. Fish farming releases feed residues and metabolic waste into the surrounding water, creating a nutrient-enriched micro-ecosystem in the lagoon. These conditions frequently trigger substantial proliferation of opportunistic macroalgae that cling naturally to aquaculture cages, ropes and nets. Rather than treating this growth as a nuisance, the research team asked a different question: what are these seaweeds made of, and could they be worth something?

To find out, the divers hand-collected approximately one kilogram of fresh biomass from each of seven seaweed taxa at depths of no more than two metres, carefully picking from multiple individuals to ensure representative sampling while minimising environmental disturbance. The samples, spanning green, brown and red macroalgal functional groups, were sealed in sterile bags, transported on ice and stored at minus 80 degrees Celsius to preserve their biochemical integrity. Because many tropical macroalgal genera are notoriously plastic in form and include cryptic species that defy visual identification, the team went beyond morphology, extracting genomic DNA and sequencing chloroplast and mitochondrial marker genes, including tufA, psbA, cox3 and rbcL, confirming species identities through nucleotide BLAST searches and depositing the sequences in GenBank.

The molecular work resolved the seven colonisers into a taxonomically diverse line-up: the green seaweeds Ulva torta in its tubular form, Ulva lactuca in its blade form and Caulerpa racemosa; the brown alga Padina sanctae-crucis lineage number two; and the red seaweeds Dasya corymbifera, Hypnea cornuta lineage number three and Gracilaria rangiferina. Each pooled sample was then subjected to a battery of validated Association of Official Analytical Chemists protocols and spectrophotometric assays, quantifying ascorbic acid, total phenolics, total flavonoids, beta-carotene, chlorophyll a and monomeric anthocyanins, with every measurement performed in triplicate.

The headline result came from the green seaweeds. Ulva torta exhibited the highest ascorbic acid concentration at 640 plus or minus 25.6 milligrams per kilogram of fresh weight, with Ulva lactuca and Hypnea cornuta close behind. Green macroalgae, with their chlorophyll-dominated photosynthetic machinery and rapid growth dynamics, are physiologically primed for ascorbate biosynthesis, which serves photoprotection and redox regulation. The authors note that these vitamin C levels are nutritionally significant and comparable to values reported in selected terrestrial plant sources, although direct comparisons warrant caution because of methodological differences. What makes the finding striking is that the biomass was growing passively within a fish farm, without targeted fertilisation or controlled cultivation, demonstrating that nutritionally valuable seaweed can occur naturally within lagoonal environments suited to Integrated Multi-Trophic Aquaculture, or IMTA.

The brown and red algae told a different chemical story. Padina sanctae-crucis dominated the secondary-metabolite league tables, posting the highest total phenolic content at 22.25 plus or minus 5.74 milligrams per kilogram fresh weight and the highest flavonoid content at 398.8 plus or minus 14.6 milligrams per kilogram. Brown algae synthesise phlorotannins, a unique class of polyphenols produced via the acetate-malonate pathway and absent from other algal lineages, compounds that serve antioxidant defence, ultraviolet screening and anti-herbivore protection in shallow, high-irradiance lagoons. The red seaweeds, meanwhile, excelled at carotenoid and pigment chemistry: Dasya corymbifera recorded the highest beta-carotene concentration at 28.18 plus or minus 2.22 milligrams per kilogram fresh weight and the highest chlorophyll a content at 24.00 plus or minus 0.05 milligrams per kilogram, while Dasya corymbifera and Gracilaria rangiferina were the only species with detectable monomeric anthocyanins, at 0.301 and 0.167 milligrams per kilogram respectively.

Statistical analysis confirmed that these differences were far from random. Analysis of variance revealed highly significant species effects across every antioxidant and pigment parameter measured, with effect sizes approaching the theoretical maximum; for chlorophyll a and anthocyanins, species identity explained essentially all of the observed variation. The authors stress an important interpretive caveat, however. Each species was represented by a single composite sample pooled from multiple individuals, so the triplicate assays reflect analytical precision rather than natural within-species variability, and the statistical comparisons describe differences among composite samples rather than estimates of biological variation across populations.

The team is equally candid about the environmental dimension of the work. Although fish farms are commonly associated with localised nutrient enrichment, dissolved nutrient concentrations were not measured during sampling, and no reference populations from non-aquaculture sites were included. The study therefore cannot establish a direct causal link between aquaculture-derived nutrients and the observed antioxidant profiles. Seaweed biochemistry is known to be strongly governed by nutrient availability: under nutrient-replete conditions, macroalgae tend to prioritise growth and accumulate proteins, chlorophylls and water-soluble vitamins such as ascorbic acid, whereas nutrient limitation shifts metabolism toward carbon-rich secondary metabolites like phenolics and flavonoids. Disentangling these nutrient-driven responses will require seasonal sampling, water-quality monitoring and comparative studies across aquaculture and non-aquaculture habitats, priorities the authors lay out for future research.

Even with those caveats, the implications for Mauritius and similar small island developing states are considerable. The global seaweed sector is worth more than eight billion US dollars annually, dominated by Asian producers, yet Mauritius, despite documenting 435 seaweed species and commanding sovereign rights over an Exclusive Economic Zone of nearly 1.9 million square kilometres, harvests seaweed only at limited artisanal scale. In an IMTA framework, seaweeds act as extractive organisms that assimilate dissolved nutrients and improve water quality while generating marketable biomass, and the new biochemical profiles provide a baseline for choosing which species to pair with finfish. Fast-growing green species such as Ulva could supply vitamin C-rich functional food ingredients, brown species like Padina could feed nutraceutical and cosmeceutical pipelines with phlorotannin-rich extracts, and red species such as Dasya corymbifera could serve as marine sources of carotenoids prized for their stability and bioactivity. The research aligns with Sustainable Development Goals 12 and 14 on responsible consumption and marine stewardship, and the authors argue that further work on seasonal variability, nutrient flux dynamics and bioavailability will be needed to translate baseline chemistry into commercial opportunity. For now, the message from the Mauritian lagoon is clear: the structures built to farm fish are also quietly growing some of the ocean’s most biochemically interesting food, and nobody is harvesting it.

Subject of Research: Antioxidant profiles of edible seaweeds colonising lagoonal aquaculture structures in Mauritius

Article Title: Lagoonal aquaculture structures support antioxidant rich edible seaweeds with potential for integrated multitrophic aquaculture in Mauritius

Article References: Dabeedass, D., Akita, S., Vieira, C., Tojo, N., Yao, F., & Nazurally, N. (2026). Lagoonal aquaculture structures support antioxidant rich edible seaweeds with potential for integrated multitrophic aquaculture in Mauritius. Discover Oceans, 3(1), Article 45. https://doi.org/10.1007/s44289-026-00157-x

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00157-x

Keywords: seaweed, aquaculture, Mauritius, antioxidants, vitamin C, IMTA, phlorotannins, beta-carotene, Ulva, blue economy, lagoon, nutraceuticals

The chemical arsenal on display is remarkable in its diversity. Brown algae of the class Phaeophyceae are dominated by phlorotannins, polyphenolic polymers built from phloroglucinol units and linked through ether, phenyl and dibenzodioxin bonds. The degree of polymerisation governs both solubility and bioactivity, and roughly 220 phlorotannin entries are catalogued in the Seaweed Metabolite Database. Red algae, which show the highest fingerprint diversity in that database with 645 recorded metabolites, specialise in sulfated galactans such as carrageenans and in an extraordinary array of halogenated terpenes and acetogenins, exemplified by compounds like elatol and isolaurinterol from the genus Laurencia. Laurencia dendroidea alone has yielded more than 40 unique terpenoids, supported by 21 identified terpene synthase genes. Green algae contribute sulfated polysaccharides known as ulvans, alongside specialised peptides with emerging biomedical relevance.

The antimicrobial mechanisms underlying these compounds are mechanistically distinct from those of classical antibiotics, which is precisely what makes them attractive in an era of multidrug resistance. Phlorotannins act through a combination of membrane disruption, chelation of essential metal ions and the generation of oxidative stress, while simultaneously interfering with quorum sensing—the chemical communication system bacteria use to coordinate virulence factor production and biofilm formation. Studies of phlorotannins from Hizikia fusiforme, for example, demonstrated both antimicrobial and anti-quorum-sensing activity. Halogenated terpenoids from Laurencia species show potent activity against Staphylococcus aureus and Vibrio species, an effect attributed to their lipophilic and electrophilic chemical character. Sulfated polysaccharides such as carrageenan and fucoidan take a different tack, interfering with bacterial adhesion and colonisation by altering electrostatic interactions at the microbial cell surface. Because these molecules hit multiple cellular targets at once, the risk of resistance emergence may be inherently lower than for single-target drugs.

The antiviral and antifungal records of these metabolites are equally striking. Sulfated polysaccharides including carrageenans and agars can mimic host cell receptors, preventing enveloped viruses from attaching to and entering target cells, while phlorotannins inhibit viral proteases and polymerases by binding to key viral proteins; a phlorotannin-rich extract of Ascophyllum nodosum has been shown to inhibit influenza infection. Against fungi, phlorotannins compromise cell wall integrity and block ergosterol biosynthesis—pathways reminiscent of synthetic antifungals but potentially less prone to resistance—while elatol exerts fungicidal effects through membrane disruption and oxidative stress. Antiparasitic activity has been traced to fatty acid derivatives and phenolic compounds that interfere with parasite metabolism and membrane stability. The review notes, however, that most of this evidence remains in vitro, and that in vivo validation in relevant animal models is urgently needed before clinical deployment.

Beyond direct pathogen killing, the most transformative dimension of the review concerns microbiome engineering. Seaweed-derived polysaccharides such as fucoidans, laminarins and ulvans act as selective prebiotics, enriching beneficial taxa such as Bifidobacterium, Lactobacillus and Akkermansia while suppressing opportunistic members of the Bacteroidetes and Proteobacteria. In broiler chickens, dietary inclusion of 5 to 10 grams per kilogram of seaweed polysaccharides improved intestinal architecture, microbial balance and weight gain in a dose-dependent manner. In pre-weaning Holstein calves, seaweed polysaccharide supplementation increased the abundance of Prevotella and Succiniclasticum, reduced diarrhoea incidence, lowered systemic inflammatory markers including IL-18, TNF-α and IFN-γ, and elevated immune effectors such as complement C3 and IgM. These effects were linked to increased abundance of gut microbes involved in alkaloid and glucocorticoid biosynthesis, suggesting a coordinated immunometabolic mechanism.

The ecological sophistication of these interactions extends to the seaweeds themselves, which the authors describe as holobionts—integrated units of alga plus microbiota. Macroalgae such as Agarophyton vermiculophyllum engage in what researchers call chemically mediated microbial gardening, dynamically attracting symbiotic microbes and excluding pathogens depending on environmental conditions like salinity. Exometabolomic analyses show that macroalgae release distinctive nitrogenous and lipid-rich compounds that support microbial colonisation and nutrient cycling, and genomic surveys have identified more than 4,400 polysaccharide utilisation loci and roughly 8,800 biosynthetic gene clusters in algae-associated bacteria—clear evidence of co-evolutionary adaptation for metabolising algal substrates. Many metabolites previously credited to seaweeds are in fact synthesised or chemically modified by their associated microbiota, a realisation that reshapes how such compounds should be discovered, sourced and standardised.

Biotechnology is now converging to solve the longstanding problems that have kept these compounds out of the clinic. On the extraction side, green technologies—ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction and enzymatic hydrolysis—are replacing crude solvent methods, improving yield, selectivity and sustainability. Natural deep eutectic solvents optimised for Fucus vesiculosus have delivered high-purity phlorotannins validated by HPLC-MS profiling. Nanotechnology offers solutions to the chronic bioavailability problem: red seaweed-derived nanoparticles provide biocompatibility and controlled release, while silver-based metal–organic frameworks embedded in κ-carrageenan hydrogels combine antibacterial action with the mechanical properties needed for wound dressings. One carrageenan–silver hydrogel composite has already entered commercial wound-healing use, and fucoidan–chitosan nanoparticles are in Phase I trials for targeted colorectal delivery of curcumin.

Synthetic biology is arguably the most ambitious frontier. Metagenomic mining of seaweed microbiota has illuminated vast biosynthetic potential in genera such as Pseudoalteromonas and Vibrio, and CRISPR-based editing combined with heterologous expression in fast-growing chassis like Vibrio natriegens is enabling high-yield biosynthesis of halogenated meroterpenes. The red algal lectin Griffithsin, produced by expression in Nicotiana benthamiana plants, has achieved preclinical validation as a topical antiviral microbicide, demonstrating industrial scalability. Bioinformatic platforms such as antiSMASH and BiG-SCAPE are accelerating the annotation of novel gene clusters encoding alkaloids, terpenoids and glycosides. On the regulatory side, the strongest proof of concept remains sodium oligomannate (GV-971), an oligosaccharide derived from marine algae that received conditional approval in China for Alzheimer’s disease following a 36-week Phase 3 trial—although the review stresses that broader global endorsement awaits more extensive chronic toxicity data.

The authors are candid about the obstacles that remain. Metabolite composition varies with season, geography, salinity, light and harvest conditions; the antimicrobial activity of Ulva lactuca extracts, remarkably, fluctuates with lunar phase at harvest. Poor oral bioavailability, low gastrointestinal stability, first-pass hepatic metabolism and batch-to-batch inconsistency in crude extracts complicate pharmacokinetic modelling and regulatory approval. Structural heterogeneity in fucoidans—where sulfation patterns and molecular weight determine bioactivity—means that harmonised analytical standards are lacking. The review calls for omics-guided bioactivity mapping, standardised extraction and assay protocols, microbiome-informed therapeutic design, and sustainable cultivation systems including land-based aquaculture and integrated multi-trophic approaches that recycle nutrients by pairing seaweed farming with fish or shellfish production. Photobioreactors and controlled tank cultures, in which salinity, light and nutrient stress can be tuned to boost production of phlorotannins, fucoidan and terpenoids, offer a path to reproducible, quality-controlled biomass.

Taken together, the evidence assembled in this review paints seaweed-derived secondary metabolites as far more than a curiosity of marine natural product chemistry. They are multimodal antimicrobials capable of attacking pathogens through mechanisms that bypass existing resistance determinants; they are prebiotic scaffolds that can rebuild dysbiotic microbial communities and dampen inflammation; and they are scaffolds for nanocarriers and synthetic biology platforms that are already reaching commercial and clinical milestones. What is needed now, the authors conclude, is interdisciplinary alignment—marine biotechnologists, pharmacologists, microbial ecologists and clinicians working within shared analytical frameworks—to convert a chemically extraordinary ocean resource into dependable, evidence-based medicines for the microbiome-centred era of healthcare.

The timing of this review reflects a broader shift in how antimicrobial research is conceptualised. Rather than seeking single molecules that sterilise microbial communities, the microecological approach emphasises selective modulation—suppressing pathogens while preserving or even enriching commensal taxa. Seaweed metabolites are unusually well suited to this paradigm because their activities span both direct antimicrobial action and substrate-level nutrition of beneficial bacteria, a dual function rarely seen in conventional small-molecule antibiotics.

The taxonomic partitioning of metabolite classes among algal phyla is itself scientifically informative. The distinct biosynthetic capabilities of Phaeophyceae, Rhodophyta and Chlorophyta mean that sourcing decisions can be guided by target compound class: phlorotannins from brown algae for antioxidant and anti-quorum-sensing applications, carrageenans and halogenated terpenoids from red algae for antiviral and antibacterial purposes, and ulvans from green algae for prebiotic formulations. This phylum-specific specialisation, catalogued in resources such as the Seaweed Metabolite Database, provides a rational framework for bioprospecting programmes.

The open-access status of the review, published as volume 3, article number 7 of Discover Biotechnology, makes the full catalogue of compound classes, mechanisms and translational case studies freely available to researchers in regions where seaweed cultivation is already an established industry. The authors’ citation record, with the article already accumulating citations and thousands of accesses within weeks of publication, suggests substantial interest in microbiome-centred alternatives to conventional antibiotics. As regulatory agencies increasingly grapple with how to evaluate complex, heterogeneous natural products, the standardisation agenda outlined by Annamalai and Kolandhasamy may prove as consequential as the molecules themselves.

Subject of Research: Bioactive secondary metabolites from marine macroalgae for antimicrobial action and microbiome modulation

Article Title: Marine macroalgal metabolites in microbial modulation for next-generation microecological therapeutics

Article References: Annamalai, A., & Kolandhasamy, P. (2026). Marine macroalgal metabolites in microbial modulation for next-generation microecological therapeutics. Discover Biotechnology, 3(1), Article 7. https://doi.org/10.1007/s44340-025-00047-6

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00047-6

Keywords: marine macroalgae, seaweed metabolites, antimicrobial resistance, phlorotannins, sulfated polysaccharides, fucoidan, carrageenan, microbiome modulation, prebiotics, synthetic biology, nanocarriers, microecological therapeutics