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The effect of UV radiation on the accumulation of mycosporine-like amino acids (MAAs) and pigments was investigated on red macroalga Palmaria palmata cultivated for 21 days. The data were combined with the effect of NaNO3 to further investigate the synthesis of these nitrogenous compounds. A progressive decrease in both total MAA and pigment contents was observed, with a positive effect of nitrate supply. Usujirene was the only MAA exhibiting a significantly increasing content when exposed to UV radiation, changing from 9% to 24% of the total MAA’s contribution, with no variation observed with NaNO3. This suggests a specific induction or synthesis pathway of usujirene for photoprotection, while the synthesis of other MAAs could have been limited by an insufficient amount of UV radiation and/or irradiance. The photoprotective ability of some MAAs could have been impacted by nitrogen starvation over time, resulting in a limited synthesis and/or potential use of MAAs as a nitrogen source for red macroalgae. The data confirmed the multiple effects of environmental factors on the synthesis of MAAs while providing new insights into the specific synthesis of usujirene, which could find an application in the cosmetics sector as natural sunscreen or an anti-ageing agent.

Brown seaweeds are attracting attention due to their richness in bioactive compounds, in particular, their phlorotannins. We present here a case study of two Fucales, Ascophyllum nodosum and Halidrys siliquosa, sustainably collected, to produce active polyphenols for the cosmetics sector. Phenolic contents of crude extracts, obtained by Accelerated Solvent Extraction (ASE), were more elevated in H. siliquosa at 100.05 mg/g dry weight (DW) than in A. nodosum (29.51 mg/g DW), considering 3 cycles with cell inversion. The temperature of extraction for a high phenolic content and high associated antioxidant activities close to positive controls was 150 °C for both algae and the use of only one cycle was enough. A semi-purification process using Solid-phase Extraction (SPE) was carried out on both ASE crude extracts (one per species). The majority of phlorotannins were found in the ethanolic SPE fraction for A. nodosum and the hydroethanolic one for H. siliquosa. The SPE process allowed us to obtain more concentrated fractions of active phenolic compounds (×1.8 and 2 in A. nodosum and H. siliquosa, respectively). Results are discussed in regard to the exploitation of seaweeds in Brittany and to the research of sustainable processes to produce active natural ingredients for cosmetics.

Since 2011, massive new strandings of holopelagic Sargassum have been reported on the coasts of the Caribbean, northern Brazil, Guiana, and West Africa, causing severe economic and ecological damage. Three common morphotypes (S. fluitans III, S. natans I, and S. natans VIII) were identified as responsible for these catastrophic events, with dominance shifts between them over time. However, the taxonomic status of these holopelagic Sargassum morphotypes remains unclear. Using an integrative taxonomy framework, combining a morphological study and molecular analyses, this study aimed to clarify their taxonomic status. Morphological analyses of 54 characters revealed no intermediate form between the three morphotypes, with the overall shape, nature of the axis, and size and shape of blades and vesicles being the most discriminating. An analysis of mitochondrial (IGS, cox2, cox3, mt16S rRNA, and nad6) and plastid (rbcL) markers confirmed the genetic divergence among the three morphotypes, with a lower level of divergence between the two S. natans morphotypes. Without additional molecular characterization, these morphotypes cannot be classified as three distinct species. However, due to their distinct morphological characteristics and sympatry within drifting aggregations, a revision of holopelagic species names is proposed, with Sargassum fluitans var. fluitans (for S. fluitans III), Sargassum natans var. natans (for S. natans I), and S. natans var. wingei (for S. natans VIII). This revision provides necessary clarity on the species involved in inundations of the tropical Atlantic.

The worldwide growing food demand and the excessive use of synthetic and chemical inputs compel the agricultural sector to find innovative and sustainable solutions to enhance or at least maintain crop yields in times of increased abiotic stresses levels linked to global change. Currently, great research efforts are carried out on brown seaweeds as their environment lead them to produce a broad range of compounds, with osmoregulatory, antioxidant, pro-bacterial, and plant-growth promoting activities. Indeed, numerous studies are looking at different combinations of algal species, extraction processes, plant species and environments of plant culture to highlight the various effects of algal extracts on plant growth and development, and resistance to abiotic stresses. Consequently, a wide variety of novel commercial products are emerging, presenting diversified chemical compositions, formulations and means of application. Such products allow the biostimulation of plants and soil by alleviating abiotic stresses such as drought, frost, and salt. The action of brown macroalgal extracts on plant and soil health has been repeatedly demonstrated, yet the precise relation between the extract chemical composition and its subsequent effect is still to be elucidated, as molecular synergy is suspected to play an important role. In this review, we present the interest of using brown macroalgal extracts to produce biostimulants with beneficial action on soil health, plant growth and development, as well as resistance against abiotic stresses, in relation to the molecular changes occurring.

Effective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are

Holopelagic Sargassum blooms in the tropical North Atlantic since 2011 are composed of two species, Sargassum natans and S. fluitans, and three morphotypes: S. natans VIII, S. natans I and S. fluitans III. The distinct morphology and the variations in space and time of the proportion of these three morphotypes suggest that they may have different physiology. For the first time, we have quantified the growth rates of these three morphotypes through in situ 9-day experiments on the coast of Martinique Island (French West Indies). Despite the non-optimal conditions for growth for these pelagic species and the short time of the experiment, we have observed that Sargassum fluitans III was growing faster (approximately twice as fast) than S. natans VIII and S. natans I. Sargassum natans I exhibited the slowest growth. The differences in tissue composition (CNP and CN natural isotopes) of morphotypes point to a greater benefit for S. fluitans III from the coastal localization of our experiment than for the two S. natans morphotypes, and suggest that S. natans I had achieved its last growth further offshore before our experiment. These contrasting growth performances are consistent with the dominance of S. fluitans III in recent observations in the Caribbean region and along the path from the Sargassum belt. This also makes this last morphotype the best candidate for cultivation. Making the distinction between the growth performances of morphotypes may improve the current predictive models about dispersal of these species.

Sargassum C. Agardh is a highly diverse genus within the brown algae, with 615 currently recognized species, varieties and forms worldwide. This high level of species diversity led early taxonomists, using morphological-anatomical criteria only, to divide the genus into up to five sub-genera and several lower-ranking taxonomic units (e.g., sections, tribes). With the advent of molecular data, subsequent authors revised this complex and archaic classification, with the genus now comprising only two sub-genera: Sargassum and Bactrophycus. Whilst most Sargassum species are benthic, only two are known to be holopelagic and responsible for strandings along tropical Atlantic coasts. The rest of the genus is cosmopolitan, occurring from tropical to temperate regions. Sargassum has not yet been reported in polar regions. Where Sargassum is present, macroalgal populations can grow in large quantities, and the resulting biomass can be valuable to the local communities for a variety of uses. Here we review the genus Sargassum from a taxonomic, ecological and physiological perspectives, and explore the different ways of taking advantage of this extraordinary biomass, which while becoming an invasive pest in some countries, could represent opportunities for coastal populations worldwide.

Marine animal by-products of the food industry are a great source of valuable biomolecules. Skins and bones are rich in collagen, a protein with various applications in food, cosmetic, healthcare, and medical industries in its native form or partially hydrolyzed (gelatin). Salmon gelatin is a candidate of interest due to its high biomass production available through salmon consumption, its biodegradability, and its high biocompatibility. However, its low mechanical and thermal properties can be an obstacle for various applications requiring cohesive material. Thus, gelatin modification by cross-linking is necessary. Enzymatic cross-linking by microbial transglutaminase (MTG) is preferred to chemical cross-linking to avoid the formation of potentially cytotoxic residues. In this work, the potential of salmon skin gelatin was investigated, in a comparative study with porcine gelatin, and an enzymatic versus chemical cross-linking analysis. For this purpose, the two cross-linking methods were applied to produce three-dimensional, porous, and mechanically reinforced hydrogels and sponges with different MTG ratios (2%, 5%, and 10% w/w gelatin). Their biochemical, rheological, and structural properties were characterized, as well as the stability of the material, including the degree of syneresis and the water-binding capacity. The results showed that gelatin enzymatically cross-linked produced material with high cross-linking densities over 70% of free amines. The MTG addition seemed to play a crucial role, as shown by the increase in mechanical and thermal resistances with the production of a cohesive material stable above 40 °C for at least 7 days and comparable to porcine and chemically cross-linked gelatins. Two prototypes were obtained with similar thermal resistances but different microstructures and viscoelastic properties, due to different formation dynamics of the covalent network. Considering these results, the enzymatically cross-linked salmon gelatin is a rel

Five native Sargassaceae species from Brittany (France) living in rockpools were surveyed over time to investigate photoprotective strategies according to their tidal position. We gave evidences for the existence of a species distribution between pools along the shore, with the most dense and smallest individuals in the highest pools. Pigment contents were higher in lower pools, suggesting a photo-adaptive process by which the decreasing light irradiance toward the low shore was compensated by a high production of pigments to ensure efficient photosynthesis. Conversely, no xanthophyll cycle-related photoprotective mechanism was highlighted because high levels of zeaxanthin rarely occurred in the upper shore. Phlorotannins were not involved in photoprotection either; only some lower-shore species exhibited a seasonal trend in phlorotannin levels. The structural complexity of phlorotannins appears more to be a taxonomic than an ecological feature: Ericaria produced simple phloroglucinol while Cystoseira and Gongolaria species exhibited polymers. Consequently, tide pools could be considered as light-protected areas on the intertidal zone, in comparison with the exposed emerged substrata where photoprotective mechanisms are essential.

Osteoporosis is an aging-related disease and a worldwide health issue. Current therapeutics have failed to reduce the prevalence of osteoporosis in the human population, thus the discovery of compounds with bone anabolic properties that could be the basis of next generation drugs is a priority. Marine plants contain a wide range of bioactive compounds and the presence of osteoactive phytochemicals was investigated in two halophytes collected in Brittany (France): the invasive Spartina alterniflora and the native Salicornia fragilis. Two semi-purified fractions, prepared through liquid-liquid extraction, were assessed for phenolic and flavonoid contents, and for the presence of antioxidant, mineralogenic and osteogenic bioactivities. Ethyl acetate fraction (EAF) was rich in phenolic compounds and exhibited the highest antioxidant activity. While S. fragilis EAF only triggered a weak proliferative effect in vitro, S. alterniflora EAF potently induced extracellular matrix mineralization (7-fold at 250 μg/mL). A strong osteogenic effect was also observed in vivo using zebrafish operculum assay (2.5-fold at 10 μg/mL in 9-dpf larvae). Results indicate that polyphenol rich EAF of S. alterniflora has both antioxidant and bone anabolic activities. As an invasive species, this marine plant may represent a sustainable source of molecules for therapeutic applications in bone disorders.

Dimethylsulfoniopropionate (DMSP) plays many important physiological and ecological roles in macroalgae. The most common method to measure DMSP is by gas chromatography analysis of the dimethylsulfide (DMS) produced after NaOH hydrolysis (pH > 12). Storage of DMS, however, is not recommended for more than a week. We investigated if acidification can be a suitable method to preserve DMSP in macroalgal samples over three months of storage, compared to widely used protocols such as drying and freezing at ‐20°C. The DMSP content of green (Ulva sp. and Ulva compressa), red (Chondrus crispus) and brown (Bifurcaria bifurcata) macroalgae were analyzed 24 h after NaOH addition (control values); and after acidification (0.2 mol · L HCl‐1) for 24 h of fresh material, followed by NaOH addition for 24 h. These values were compared to measurements after 3‐month storage of samples that had been either dried in a heater (60°C for a night, and storage at room temperature), or frozen at ‐20°C, or kept in 0.2 mol · L HCl‐1. There was no significant difference between DMSP measurements on freshly collected material and after acidification of the samples, whether 24 h later or after 3 months of storage. This was in contrast with 3‐month storage protocols involving overnight drying at 60°C (75‐98% DMSP loss), and to a lesser degree freezing at ‐20°C (37‐80% DMSP loss). We thus advise to acidify macroalgal samples for preservation over long periods of time rather than drying or freezing, when assaying DMSP content.

This review focuses on the diversity of French tropical overseas macroalgae and their biotechnological applications. After listing the specific diversity, i.e. 641 species in French Antilles in the Atlantic Ocean, 560 species in the Indian Ocean, and 1015 species in the South Pacific Ocean, we present the potential of their metabolites and their main uses. Among the great diversity of metabolites, we focus on carbohydrates, proteins, lipids, pigments and secondary metabolites, in particular terpenes and phenolic compounds. The main applications of reef macroalgae are described in human and animal consumptions, phycocolloids extraction, production of active ingredients for health, cosmetics, agriculture, and bioremediation. For each application, we list what has been done, or will be done in French tropical overseas territories and point out the challenges faced when using this chemo-diversity, and problems linked to their exploitation. Finally, we discuss challenges to develop seaweed farming, their uses in carbon sequestration and resilience to global change, their uses for alternative proteins together with the production of bioenergy and biomaterials. As a conclusion, we encourage the research on the chemo-diversity of French reef macroalgae for industrial applications as these organisms represent a reservoir of active ingredients that is still insufficiently explored.

The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.

Marine macroalgae represent a valuable natural resource for bioactive phytochemicals with promising applications in therapeutics, although they remain largely under-exploited. In this work, the potential of two marine green macroalgae (Cladophora rupestris and Codium fragile) as a source of bioactive phenolic compounds was explored, and antioxidant, mineralogenic, and osteogenic activities were evaluated. For each species, a crude hydroalcoholic extract (CE) was prepared by solid/liquid extraction and fractionated by liquid/liquid purification into an ethyl acetate fraction (EAF) enriched in phenolic compounds and an aqueous fraction (AF). Antioxidant activity, assessed through radical scavenging activity and reducing power assay, was increased in EAF fraction of both species and closely related to the phenolic content in each fraction. Mineralogenic activity, assessed through extracellular matrix mineralization of a fish bone-derived cell line, was induced by EAF fractions (up to 600 % for C. rupestris EAF). Quantitative analysis of operculum formation in zebrafish larvae stained with alizarin red S further confirmed the osteogenic potential of EAF fractions in vivo, with an increase of more than 1.5-fold for both C. fragile and C. rupestris fractions, similar to vitamin D (control). Our results demonstrated a positive correlation between phenolic fractions and biological activity, suggesting that phenolic compounds extracted from marine green macroalgae may represent promising molecules toward therapeutic applications in the field of bone biology.

The present study focused on a brown macroalga (Halidrys siliquosa), with a particular emphasis on polyphenols and their associated biological activities. Two fractions were obtained by liquid/liquid purification from a crude hydroethanolic extract: (i) an ethyl acetate fraction and (ii) an aqueous fraction. Total phenolic contents and antioxidant activities of extract and both fractions were assessed by in vitro tests (Folin-Ciocalteu test, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, reducing power assay, superoxide anion scavenging assay, and beta-carotene-linoleic acid system). For the most active fraction, i.e., the ethyl acetate fraction, the oxygen radical absorbance capacity (ORAC) value, antibacterial activities, and sunscreen potential (Sun Protection Factor and UV-A-Protection Factor) were tested in vitro. A high correlation found between antioxidant activities and total phenolic content was interpreted as the involvement of polyphenolic compounds in antioxidant mechanisms. Interestingly, the ethyl acetate fraction appeared to be a broad-spectrum UV absorber and showed a strong bactericidal activity against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. In this fraction, four phenolic compounds (trifuhalols and tetrafuhalols and, for the first time, diphlorethols and triphlorethols) were identified using 1D and 2D nuclear magnetic resonance (NMR) and MS analysis. These findings are promising for the use of H. siliquosa, abundant in Brittany, as a valuable source of photoprotectant molecules for sunscreen and cosmetic applications.

The wide polarity range and highly polar compounds of two selected red seaweed, Grateloupia turuturu and Palmaria palmata were extracted using two different types of solvent, dichloromethane/methanol and methanol/water. Monthly in vitro antibacterial activities were studied using the microplate method against the marine bacteria Vibrio harveyi strain ORM4, known to infect abalone. Inhibition, slowdown and delay of Vibrio harveyi growth were investigated. Polar compounds of seaweed showed an activity against the abalone pathogen. The best activity was recorded from P. palmata collected in spring, with an inhibition of 7.9% of the bacterial growth. Preliminary 1H NMR profiles identified the differences between the extracts.