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