The review integrates perspectives from Earth system ecology, biogeochemistry, and spatial analysis to evaluate three interdependent dimensions: the saturation of habitable terrestrial space, the relative openness yet ecological constraint of marine environments, and the dynamic coupling between atmospheric CO2 and ocean chemistry. What emerges is a fundamental asymmetry between land and ocean systems. Terrestrial ecosystems are undergoing direct structural transformation through land-use change, resulting in a measurable contraction of ecologically functional space and increasing transgression of planetary boundaries. Marine systems, by contrast, retain substantial geometric space but are subject to diffuse, cumulative stressors, particularly in productive coastal zones where macroalgal communities are most viable.

The quantitative evidence for terrestrial saturation is stark. Global human modification and Human Footprint datasets show that approximately 75 percent of the planet’s land surface experiences measurable human pressure, with only roughly 43 percent of terrestrial lands in 2022 remaining at very low modification and 10 percent already highly modified. Between 1990 and 2020, 24 percent of terrestrial ecosystems, spanning 31 million square kilometres, increased in modification. From 2000 to 2018, more than 2 million square kilometres of wilderness were lost, with mangrove-dominated biomes suffering over 5 percent wilderness loss, illustrating strong coastal pressure zones. These pressures translate into substantial local biodiversity impacts, with land-use conversion and degradation having already reduced local terrestrial species richness by 13.6 percent on average and total abundance by 10.7 percent.

The worst-affected habitats show even more dramatic declines, with 76.5 percent reductions in local richness and 39.5 percent reductions in abundance. When community completeness is considered, highly impacted regions retain on average less than 20 percent of their regionally suitable plant species locally, compared with about 35 percent in areas with minimal human footprint. Human consumption patterns further externalize terrestrial biodiversity loss, with food consumption alone accounting for about 40 percent of global biodiversity loss and more than half of the biodiversity loss driven by consumption in developed economies occurring outside their borders. The terrestrial signal is one of pervasive, spatially extensive, and often chronic proximity between plants and intense anthropogenic modification.

Marine macroalgae, commonly referred to as seaweeds, occupy an environment that differs markedly in its exposure to these constraints. The marine realm, while not exempt from human impact, offers vast spatial continuity, distinct carbon dynamics, and in certain contexts reduced direct exploitation compared to terrestrial systems. However, macroalgal communities are strongly impacted by climate-driven extremes and local coastal stressors. Anthropogenic stressors affecting them include ocean warming and marine heatwaves, overfishing of herbivore predators, eutrophication, pollution, and marine litter. Climate change-related warming and heatwaves stand out as pervasive threats for marine foundation species including kelps, often acting synergistically with other stressors such as overfishing and coastal development.

The consequences of these episodic but intense marine impacts are vividly illustrated by specific case studies. Bull kelp forests in northern California lost more than 90 percent of canopy along more than 350 kilometres of coastline following a marine heatwave and sea star mass mortality, leading to persistent urchin barrens and approximately 80 percent abalone mortality. Another study documented a 95 percent reduction in giant kelp canopy and a 2,485 percent increase in herbivore densities in a subregion of Baja California after extreme heatwaves, with shifts to urchin barrens as alternative stable states. In Tasmania, early warning incipient barrens expanded along 500 kilometres of coast, with projections that about 50 percent of kelp beds in the range extension region may collapse by 2030. These changes are often abrupt, spatially contagious, and strongly linked to warming interacting with predator overfishing and herbivore release.

Not all macroalgal responses are negative, however. Warming and eutrophication can also drive blooms and spatial expansion of some macroalgae. Biomass of the brown alga Sargassum horneri in the East China and Yellow Seas increased from 2000 to 2021, primarily linked to ocean warming, while green alga Ulva prolifera increases appear to reflect combined warming and coastal human activities such as aquaculture. Tropical macroalgal reefs can be natural and productive components of tropical seascapes, and high macroalgal cover is not always an anthropogenic symptom and may support fisheries and productivity where herbivore communities and connectivity remain intact. Yet these localized increases in productivity do not translate into the kind of long-term carbon sequestration and ecosystem stability that terrestrial vegetation provides.

The biogeochemical role of macroalgae differs fundamentally from that of terrestrial plants. While macroalgal communities can exhibit high rates of primary production, a substantial proportion of this biomass is rapidly remineralized within the marine environment. Only a fraction is exported to deep ocean sinks where long-term sequestration can occur. Consequently, the capacity of macroalgae to offset atmospheric CO2 increases is constrained by ocean circulation, decomposition processes, and ecological feedbacks, limiting their effectiveness as a global carbon sink despite high local productivity. This distinction is critical, as compensation for terrestrial loss would require not only equivalent production but also comparable contributions to long-term carbon storage and ecosystem stability. Terrestrial plants contribute significantly to long-term carbon storage through biomass accumulation and soil formation, whereas a substantial fraction of macroalgal production is rapidly remineralized, with only limited transfer to long-term oceanic carbon sinks.

The temporal dimension of these processes reveals a critical mismatch between terrestrial degradation and marine response. Land-use change operates on relatively rapid timescales, leading to immediate and often irreversible loss of plant communities. In contrast, marine responses to elevated CO2 and associated environmental changes unfold more gradually due to the lag in oceanic carbon uptake. This creates a period of systemic disequilibrium in which terrestrial primary production is declining or becoming spatially constrained, while marine productivity may be temporarily enhanced but remains unstable and subject to increasing stress. Such a mismatch precludes a synchronous or balanced compensation between the two domains. The susceptibility of macroalgal systems to abrupt regime shifts introduces an additional layer of uncertainty, as climate-driven disturbances and trophic imbalances can rapidly transform productive ecosystems into low-functioning states.

Taken together, these findings indicate that the Earth system is not undergoing a balanced redistribution of primary producers from land to sea, but rather a transition toward a new configuration characterized by reduced terrestrial complexity and increasingly stressed marine systems. The rise in atmospheric CO2 may transiently enhance certain aspects of marine productivity, but this effect is tightly coupled to processes that ultimately constrain and destabilize marine ecosystems. The decline of terrestrial phytosociological systems represents not a shift in location of primary production, but a net reduction in the resilience and integrity of the biosphere as a whole. The authors conclude that the notion of marine macroalgae as a compensatory mechanism for terrestrial vegetation loss is not supported under current understanding of Earth system constraints, and they underscore the urgency of conserving remaining terrestrial ecosystems while simultaneously mitigating cumulative impacts on marine environments, recognizing that neither domain can substitute for the ecological functions of the other.

Subject of Research: Functional saturation of terrestrial and marine ecosystems under anthropogenic pressure

Article Title: Functional saturation of Earth’s habitable domains: constraints on land systems and potential in marine environments

Article References: Petrescu-Mag, I. V., Oroian, I. G., Păsărin, B., Safirescu, O. C., Burduhos, P., Braşovean, I., Bordea, D., Moldovan, B., Pojar, T. N., Bănățean-Dunea, I., Oroian, F. C., & Pandey, P. (2026). Functional saturation of Earth’s habitable domains: constraints on land systems and potential in marine environments. Frontiers in Systems Biology, 6, Article 1941138. https://doi.org/10.3389/fsysb.2026.1941138

Image Credits: AI Generated

DOI: 10.3389/fsysb.2026.1941138

Keywords: functional saturation, terrestrial ecosystems, marine macroalgae, planetary boundaries, ocean acidification, biodiversity loss, carbon sequestration, regime shifts, land-use change, biosphere resilience, primary productivity, Earth system ecology

MAAs occupy a unique niche in biology. To date, only cyanobacteria, phytoplankton, and algae are known to synthesize them, and more than 570 species of marine macroalgae are thought to harbor the compounds. Their chemical structures are diverse, their light and thermal stability is excellent, and they are considered non-toxic, qualities that have long made them attractive candidates for cosmetics and pharmaceuticals. Yet their antioxidant behavior has remained surprisingly understudied, particularly in comparison with the polysaccharides, phenols, and pigments that dominate the seaweed antioxidant literature. The Jiangsu team, led by Yingying Sun, set out to close that gap by focusing on six species that are common in Chinese waters and cuisine: Bangia fuscopurpurea, Gelidium amansii, Sargassum fusiforme, Palmaria palmata, Sargassum sp., and Undaria pinnatifida.

The first hurdle was cosmetic in the most literal sense. In the researchers’ earlier work, MAA extracts from several of these algae came out stained black-red or black-green by co-extracted pigments, which muddied subsequent activity assays and complicated any practical application. Their solution was elegantly simple: wash the dried, powdered algae with anhydrous ethanol before the real extraction begins, discarding the pigment-laden supernatant. Spectrophotometric scans confirmed the wash was pulling out chlorophyll, phycobiliproteins, and beta-carotene, the compounds responsible for the unwanted color. Only then did the team extract the MAAs themselves using 25 percent methanol at 45 degrees Celsius, followed by repeated rounds of cold ethanol precipitation to strip away remaining non-target material.

The results of this pretreatment were striking. The purified extracts emerged a transparent reddish hue rather than an opaque dark sludge, and for two species the yield actually improved rather than suffered. Bangia fuscopurpurea delivered 1.5 times its previous MAA output, reaching a yield of 23.62 percent of the dried algal powder, while Gelidium amansii improved by a factor of 1.1. For the brown algae, the trade-off was less favorable: yields of Sargassum fusiforme, Sargassum sp., and Undaria pinnatifida declined significantly, suggesting that some MAAs were lost during the extra purification steps and that the protocol will need species-specific refinement. High-performance liquid chromatography coupled with mass spectrometry showed that the cleanup did not alter the underlying chemistry. The extracts were dominated by four familiar MAAs: palythine, palythenic acid, shinorine, and porphyra-334. Notably, the team reports the first detection of palythenic acid in Palmaria palmata, a compound previously known mainly from phytoplankton and a handful of other macroalgal species.

With clean extracts in hand, the antioxidant testing began. Using a Trolox-based assay, the researchers found that the total antioxidant capacity of the extracts from Bangia fuscopurpurea and Sargassum fusiforme towered over the rest, running 1.8 to 5.1 times higher than the other four species. The superoxide anion scavenging assay told a similar story. At a concentration of 50 milligrams per milliliter, the extracts from Sargassum fusiforme, Bangia fuscopurpurea, and Sargassum sp. neutralized more than 93 percent of the superoxide radicals in solution, while the remaining three species still managed above 64 percent. The half-maximal effective concentrations for the two standouts hovered around 30 milligrams per milliliter. Vitamin C, it should be said, remains the benchmark, achieving over 96 percent scavenging at a mere 0.035 milligrams per milliliter, so the MAAs are not about to displace ascorbic acid on potency alone.

But potency is not the whole story, and the authors point to a mechanistic nuance that could change the calculus. Earlier studies have shown that although porphyra-334 and shinorine score modestly in DPPH radical assays, they are remarkably effective at quenching free radicals through hydrogen atom transfer, a different chemical pathway. The relatively low concentration of active MAAs within the crude extracts may also be masking their true capability, and the researchers anticipate that further purification could substantially boost performance. There is even suggestive evidence that MAA antioxidant activity contributes to inhibiting cancer cell activity, though that frontier remains exploratory.

Perhaps the most immediately practical finding concerns browning, the enzymatic discoloration that turns a sliced apple or yam an unappetizing brown within hours and drives consumer rejection of fresh-cut produce. When the team soaked yam slices and red Fuji apple slices in dilute MAA solutions and tracked them over three days, the untreated controls browned dramatically while the treated slices stayed visibly fresh. The extracts from Bangia fuscopurpurea and Sargassum fusiforme performed best, and a component isolated from the Bangia extract via silica gel chromatography outdid them all, suppressing browning in more than 52 percent of yam and apple slices after 48 hours. That performance exceeded what has been reported for green tea extract, a standard natural anti-browning agent. The researchers speculate the effect may be linked to the impressive moisture-absorption and retention properties previously documented for Bangia MAAs, though the precise mechanism awaits further study.

Safety and formulation matter just as much as activity for any food additive, and here the mineral analysis delivered reassuring news. Inductively coupled plasma optical emission spectrometry revealed that the extracts are rich in essential macro-elements such as calcium, potassium, magnesium, sodium, and phosphorus, along with beneficial trace elements including iron, zinc, copper, and molybdenum. Critically, no harmful heavy metals, lead, cadmium, arsenic, or mercury, were detected, and copper levels sat far below the limits set by the Chinese Pharmacopoeia. The team then stress-tested the two star extracts against five common food additives over 40 days at both 25 and 48 degrees Celsius. Citric acid proved destructive, cutting absorbance by more than 23 percent for the Bangia extract and over 40 percent for the Sargassum extract by the experiment’s end, while sodium glutamate also destabilized the Bangia extract. Agar and carrageenan, by contrast, actually enhanced stability, making them natural formulation partners.

The convergence of these findings, cleaner and higher-yielding extraction, demonstrated antioxidant and anti-browning activity, a benign mineral profile, and compatibility with common food hydrocolloids, sketches a credible path from laboratory bench to grocery shelf. The authors are careful to note the limitations: yields for the brown algae need improvement, antioxidant potency trails vitamin C, and the anti-browning mechanism remains unexplained. Future work will expand the evaluation to weight loss, texture, color, and visual quality of treated produce, and will probe the health-food applications of the Sargassum fusiforme and Bangia fuscopurpurea extracts in greater depth. Still, the study marks a first on several fronts, from the mineral content analysis to the food-additive stability data, and it strengthens the case that the ocean’s humble seaweeds, already hailed as biorefineries and super plants of sustainable development, hold molecules capable of keeping our food fresher and perhaps our bodies healthier.

Subject of Research: Optimized extraction and antioxidant application of mycosporine-like amino acids from marine macroalgae

Article Title: Research on the optimization of preparation and the application analysis of antioxidant activity of mycosporine-like amino acids derived from marine macroalgae

Article References: Li, Y., Wang, J., Wang, S., Jiang, X., Shi, S., & Sun, Y. (2025). Research on the optimization of preparation and the application analysis of antioxidant activity of mycosporine-like amino acids derived from marine macroalgae. Blue Biotechnology, 2(1), Article 2. https://doi.org/10.1186/s44315-025-00023-z

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00023-z

Keywords: mycosporine-like amino acids, marine macroalgae, antioxidant activity, seaweed, food preservation, anti-browning, palythine, shinorine, porphyra-334, extraction optimization, food additives, blue biotechnology

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