Sargassum Fluitans Research Articles

Investigating the Inhibitory Effect of Sargassum natans and Sargassum fluitans Extracts on Iron Corrosion in 1.00 mol L−1 HCl Solution

This study deals with the efficacy of extracts of Sargassum natans and Sargassum fluitans, an invasive brown algae present in Guadeloupe, as novel and environmentally friendly corrosion inhibitors for iron in 1 mol L−1 hydrochloric acid solutions. Six different Sargassum extracts (SE) were obtained using Soxhlet extraction with ethyl acetate, acetone, and ethanol, respectively, as solvents; cold successive maceration with chloroform and methanol, respectively; and microwave-assisted extraction with water. Subsequent electrochemical analysis showed that extracts from ethanol and ethyl acetate exhibited remarkable inhibition efficiencies of, respectively, 72.6% and 70.2%, but the better one was the extract of the cold maceration from chloroform with an inhibition efficiency of 92.0%. These findings allow us to focus on the chloroform extract (SEd) in order to see the change happening during the corrosion process via SEM and EDX analyses. Also, NMR analysis was conducted to identify the main chemicals responsible for the anticorrosion effect. The successful demonstration of the corrosion inhibitor effectiveness of extracts of Sargassum natans and fluitans suggests a potentially valuable use for this invasive biomass. These encouraging results warrant further investigation to identify and elucidate the active inhibitors in these extracts to deepen our understanding of their mechanisms for corrosion prevention and potentially expand their utility as an environmentally conscious approach to corrosion control.

Invasive brown algae (Sargassum spp.) as a potential source of biocontrol against Aedes aegypti

Influxes of sargassos are responsible for economic and environmental disasters in areas where they bloom, especially in regions whose main income relies on tourism and with limited capacity for sanitation and public health response. A promising way of valorization would be to convert this incredible biomass into tools to fight the deadly vector mosquito Aedes aegypti. In the present study, we generated hydrolates and aqueous extracts from three main Sargassum morphotypes identified in Guadeloupe (French West Indies): Sargassum natans VIII, Sargassum natans I and Sargassum fluitans. We conducted a chemical characterization and a holistic evaluation of their potential to induce toxic and behavioral effects in Ae. aegypti. Despite the low insecticidal potential observed for all the extracts, we found that S. natans VIII and S. fluitans hydrolates deterred oviposition, induced contact irritancy and stimulated blood feeding behavior in host seeking Ae. aegypti females, while aqueous extracts from S. natans I and S. fluitans deterred both blood feeding behavior and oviposition. Chemical characterization evidenced the presence of phenylpropanoid, polyphenols, amino acids and esters. Thus, Sargassum spp. aqueous extracts and hydrolates could be used to manipulate Ae. aegypti behavior and be valorized as control tools against this mosquito.

Protection against Atmospheric Corrosion of Zinc in Marine Environment Rich in H2S Using Self-Assembled Monolayers Based on Sargassum fluitans III Extract

The self-assembled monolayers (SAMs) process is one of the techniques used for the production of ultra-thin layers. The present work is therefore devoted to the study of the inhibition of zinc corrosion in a marine environment rich in H2S by SAMs based on Sargassum fluitans III. The protective effect of crude extracts of Sargassum fluitans on the surface of zinc using the SAMs process was evaluated by gravimetry and impedance on two different sites after three months of exposure. The formation of SAMs was characterized by FTIR, and the corrosion products formed on the surfaces were analyzed by XRD. The results obtained show that SAMs based on Sargassum fluitans III effectively inhibit zinc corrosion.

Anticancer Activity of Sargassum fluitans Extracts in Different Cancer Cells.

The arrival of large quantities of Sargassum in the Mexican Caribbean Sea has generated major environmental, health and economic problems. Although Sargassum has been used in the generation of some commercial products, few studies have described its possible applications as a source of compounds with anticancer activity. This study aimed to evaluate the antiproliferative effects of different Sargassum extracts on various cancer cell lines. Furthermore, LC/QTOF-MS was used to identify the compounds related to the antiproliferative effect. First, determination of the seaweed was performed, and dichloromethane, chloroform and methanol extracts were obtained. The extracts were evaluated for their antiproliferative effects by MTT in breast (MDAMB- 231 and MCF-7), prostate (DU-145), lung (A549) and cervical (SiHa) cancer cell lines. Finally, LC/QTOFMS identified the compounds related to the antiproliferative effect. The authentication showed Sargassum fluitans as the predominant species. The extracts of dichloromethane and chloroform showed an antiproliferative effect. Interestingly, the fractionation of the chloroform extract showed two fractions (FC1 and FC2) with antiproliferative activity in MDA-MB-231, SiHa and A549 cancer cell lines. On the other hand, three fractions of dichloromethane extract (FD1, FD4 and FD5) also showed antiproliferative effects in the MDA-MB-231, MCF-7, SiHa and DU-145 cancer cell lines. Furthermore, LC/QTOF-MS revealed the presence of eight major compounds in FC2. Three compounds with evidence of anticancer activity were identified (D-linalool-3-glucoside, (3R,4S,6E,10Z)-3,4,7,11-tetramethyl-6,10-tridecadienal and alpha-tocotrienol). These findings showed that Sargassum fluitans extracts are a possible source of therapeutic agents against cancer and could act as scaffolds for new drug discovery.

Changes in holopelagic Sargassum spp. biomass composition across an unusual year

The year 2021 marked a decade of holopelagic sargassum (morphotypes Sargassum natans I and VIII, and Sargassum fluitans III) stranding on the Caribbean and West African coasts. Beaching of millions of tons of sargassum negatively impacts coastal ecosystems, economies, and human health. Additionally, the La Soufrière volcano erupted in St. Vincent in April 2021, at the start of the sargassum season. We investigated potential monthly variations in morphotype abundance and biomass composition of sargassum harvested in Jamaica and assessed the influence of processing methods (shade-drying vs. frozen samples) and of volcanic ash exposure on biochemical and elemental components. S. fluitans III was the most abundant morphotype across the year. Limited monthly variations were observed for key brown algal components (phlorotannins, fucoxanthin, and alginate). Shade-drying did not significantly alter the contents of proteins but affected levels of phlorotannins, fucoxanthin, mannitol, and alginate. Simulation of sargassum and volcanic ash drift combined with age statistics suggested that sargassum potentially shared the surface layer with ash for ~50 d, approximately 100 d before stranding in Jamaica. Integrated elemental analysis of volcanic ash, ambient seawater, and sargassum biomass showed that algae harvested from August had accumulated P, Al, Fe, Mn, Zn, and Ni, probably from the ash, and contained less As. This ash fingerprint confirmed the geographical origin and drift timescale of sargassum. Since environmental conditions and processing methods influence biomass composition, efforts should continue to improve understanding, forecasting, monitoring, and valorizing sargassum, particularly as strandings of sargassum show no sign of abating.

Morphological and Molecular Characters Differentiate Common Morphotypes of Atlantic Holopelagic Sargassum

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.

Pelagic Sargassum as a Potential Vector for Microplastics into Coastal Ecosystems

Macroalgal blooms are increasing globally, with those linked to pelagic Sargassum affecting over 30 nations since 2011. As Sargassum mats traverse the Atlantic Ocean and the Caribbean Sea, they entrap and transport plastic to coastal areas, intensifying pollution in diverse ecosystems. This research assessed microplastics (MPs) within Sargassum fluitans III collected from the northern Mexican Caribbean coast (March 2021 to January 2022). The study employed a hydrogen peroxide protocol for macroalgae pretreatment to optimize MP extraction. All samples analyzed contained MPs at monthly mean concentrations that ranged from 3.5 to 15.3 MPs g−1 DW, with fibers constituting ≥90%. Fiber colors, mainly transparent, blue, and black, exhibited diverse sizes and wear stages. The study underscores the pervasive and consistent presence of MPs in pelagic Sargassum reaching the Mexican Caribbean. Considering the documented Sargassum influxes to this coast in recent years (2789–11,297 tons km−1 yr−1), potential annual MP influxes range from 0.1 × 109 to 17.3 × 109 km−1 yr−1. Efficiently removing beach-cast Sargassum and directing it to landfills could serve as a viable strategy for the simultaneous removal of attached MPs from the ocean and coastal waters, offering a promising mitigation strategy to combat plastic pollution in the examined marine environment.

Implications of changing Caribbean coral reefs on Diadema antillarum larvae settlement

Tropical western Atlantic reefs have gradually shifted from being dominated by corals to being mainly covered by macroalgae. The mass-mortality of the sea urchin Diadema antillarum in the 80s and the slow to non-existent recovery exacerbated this shift. Chemical cues associated with these reefs are expected to have shifted too with potential negative effects on larval recruitment, possibly limiting recovery of important species like D. antillarum. In this study, we tested the effects of naturally derived biofilm and macroalgae species native to Caribbean coral reefs on the settlement rate of cultured D. antillarum larvae in two separate experiments. Crustose coralline algae (CCA) were included in both experiments, making it possible to compare settlement rates from both experiments. A biofilm of one week old yielded significantly lower settlement rates compared to two, four, and six weeks old biofilm and the highest settlement rate was found for CCA with over 62% of total larvae. All six tested macroalgae species resulted in settled larvae, with little significant difference between algal species, partly due to a high variation in settlement rates within treatments. Sargassum fluitans induced the highest settlement rate with 33%, which was not significantly different from CCA with 29%. We conclude that dominant macroalgae species likely to be encountered by D. antillarum on shifted reefs are no major constraint to settlement. Our findings increase the understanding of alternative stable state settlement dynamics for a keystone coral reef herbivore.

Growth and photosynthetic physiology of holopelagic Sargassum (Phaeophyceae) under laboratory conditions

SummarySpecies of holopelagic Sargassum are responsible for Caribbean golden tides, commonly known as ‘Sargassum events’. These events mainly comprise Sargassum fluitans and Sargassum natans I, which are exposed to high levels of irradiance, but also self‐shading within their floating masses. In this study, we grew S. fluitans and S. natans I and acclimated them to low‐light conditions at 23°C in the laboratory to explore their responses to increasing light intensities. Photosynthesis, respiration, growth, and pigment content were evaluated over 3 weeks. S. fluitans and S. natans I photoacclimate to higher irradiances by decreasing their chlorophyll a and c contents. An increase in maximum photosynthesis and respiration rates was observed under high light, although differences occurred in the saturation irradiance and the initial slope of the photosynthesis versus irradiance curve. These adjustments were reflected in S. fluitans daily growth (from 2% to 7% d−1 at low to high light, respectively) and tissue nitrogen content (1.6–2.7%) but were absent in S. natans I (~1% d−1). The photosynthetic physiology of S. fluitans under these conditions suggests lower light requirements without compromising growth; however, under high light a higher photosynthetic performance was observed. Combining physiological and growth studies in holopelagic Sargassum species will serve as a baseline to understand and explain the success and overgrowth of these species along the Caribbean coast.

Molecules from Sargassum algae as Green Inhibitor for C38 in HCl Medium: Extraction, Characterization and Electrochemical Study

The aim of this work is to develop new organic bio-sourced inhibitors that are ecofriendly and biodegradable. These natural inhibitors are organic, non-toxic molecules derived from plant extracts, containing numerous secondary metabolites, and are capable of being highly effective in protecting metals against corrosion. This study concerns the extraction, characterization and electrochemical study of natural organic compounds extracted from a species of Sargassum abundant on the coasts of Martinique, Sargassum fluitans III. The objective is to inhibit the corrosion of carbon steel. Electrochemical impedance spectroscopy (EIS) and linear polarization (LP) techniques have led to new experimental results showing inhibitor efficacy. The results obtained show that this plant extract could serve as an effective inhibitor for the C38 steel in acidic media. Studies on the phytochemicals of the crude extract were also carried out. Electrochemical studies, on each chemical families present, were also established to find the main constituents responsible for corrosion inhibition properties of the algae extract. The adsorption of Sargassum fluitans III extract on the C38 steel surface, obeys the Langmuir adsorption isotherm.

Integrative Literature Analysis of Holopelagic Sargassum (Sargasso) in the Western Atlantic (2011–2022): Status, Trends, and Gaps

Since 2011, the Caribbean and Gulf of Mexico coasts have been receiving massive influxes of holopelagic sargasso algae composed of Sargassum natans and Sargassum fluitans. This phenomenon has been causing several negative local impacts, such as ecological disturbances and socioeconomic and health concerns of communities in impacted areas. This work aimed to assess the status of scientific knowledge related to pelagic sargasso, including trends, emphases, and gaps. A literature review was conducted on publications and reports from 2011 to 2022, of which 251 articles were collected based on an inclusion–exclusion criteria. Aspects of each article were quantified, including location, description of sargasso, the type of study, and research theme. A region-wide research emphasis on ecology, remote sensing, and valorization was observed. Areas first affected by the inundations composed a higher percentage of sargasso studies than other locations, and the distribution of studies varied among subregions. Topics requiring further investigation include sargasso’s growth and mortality rates and drivers, taxonomic and physiologic differences among morphotypes, and real-time forecasting resolution at local scales both on and offshore. This research emphasized efforts from the scientific community on research and mitigation initiatives.

Parametric Modelling Study to Determine the Feasibility of the Co-Gasification of Macroalgae and Plastics for the Production of Hydrogen-Rich Syngas

Seaweed is of importance to the environment due to properties such as its CO2 sequestration capability. On the other hand, plastic is a versatile material important to society. Unfortunately, the abundance of both plastics and seaweed represents a challenge due to the need of adequate waste management. At first, algae and plastics might not appear suitable for energy recovery; however, with co-gasification, the results are promising. This work presents a model to simulate the co-gasification of Chlorella vulgaris, Sargassum fluitans, and Sargassum natans with plastics. The effect of the gasification temperature (650–850 °C), equivalence ratio (0.25–0.45), and plastics/biomass ratio (0.0–1.0) on the produced gas’s lower heating value, tar concentration, and composition is assessed. Moreover, the environmental performance of using plastic to enhance the syngas produced from the co-gasification with sargassum is assessed using the life cycle assessment methodology. The results indicate that the lower heating value increases with the temperature and plastics/biomass ratio. Moreover, tar increases with the quantity of plastics, varying between 20 and 50 g/Nm3. Finally, adding plastics to algae during gasification reduces the variability in the syngas composition, simplifying the post-processing stage. With respect to environmental performance, gasification has an impact similar to those of pyrolysis and recycling, but the performance could improve with sufficient research and development.

Aerobic biotransformation of Sargassum fluitans in combination with sheep manure: optimization of control variables

ABSTRACT Sargassum fluitans was composted alongside sheep manure, in a transformative process that significantly enhanced the algal material’s properties. Post the screening/washing/screening pretreatment, the content of total volatile solids escalated to 73.20%, while ash content reduced to 16.45%. Concurrently, lignin values surged to 30.12% as the biodegradability factor declined to 21%. The pretreatment decreased electrical conductivity from 11.60 to 1.32 DS/m. Employing a central composite design and response surface analysis pinpointed the optimal substrate combinations for carbon/nitrogen ratios of 35:1 and 25:1. The chosen combinations presented a high coefficient of determination (R2 = 0.9589, carbon/nitrogen ratio; R2 = 0.6584, pH), indicative of a robust statistical fit. Over a 45-day period, composting was conducted using bioreactors or biopiles, maintaining near-neutral pH values and temperatures slightly above ambient levels. The composting process reduced up to 94% of fecal coliforms in the 1:1 combination. Physicochemical analyses confirmed that the final product is a valuable compost-soil improver, with great potential for usage in organic agriculture, reforestation, and urban green spaces. Hence, this research underscores composting as an efficient technique in managing organic waste, including the emergent and seasonal Sargassum fluitans, thus addressing a pressing environmental concern with an innovative, effective solution.

Effects of extracting solvents on phytochemical, antioxidant, and antibacterial activity of some seaweeds from the Bay of Bengal offshore Island

Seaweed is a rich source of bioactive compounds. Therefore, searching of natural antioxidant and antibacterial agents as alternatives to a synthetic counterpart is of great interest. The effects of various extracting solvents (viz. methanol, ethanol, and acetone) on the phytochemical content, antioxidant, and antibacterial activity of seven seaweeds consisting of three brown seaweeds (Sargassum natans, Sargassum fluitans, Spatoglossum asperum), three red seaweeds (Hypnea pannosa, Hypnea musciformes, Porphyra linearis) and one green seaweed (Ulva lactuca) were evaluated. The antioxidant capacity of crude extracts was evaluated by total antioxidant activity (TAA), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and cupric reducing antioxidant capacity (CUPRAC) assays. Seaweed extracts were also tested against Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, and Pseudomonas aeruginosa by agar well diffusion method. The total phenolic content (TPC) of seaweed extracts varied significantly (P < 0.05) ranging from 51.08 ± 0.72–74.62 ± 1.15 mg GAE/g. Methanolic extracts of S. natans showed significantly the highest TPC, total flavonoid content (79.22 ± 5.21 mg QE/g), and TAA (57.79 ± 4.35 mg AA/g) than other seaweed extracts. Methanolic extracts of S. natans also exhibited the highest DPPH and ABTS radical scavenging effects (EC50 = 0.74 ± 0.04 and 0.14 ± 0.01 mg/ml, respectively). While, methanolic and ethanolic extracts of S. natans showed significantly the highest effective concentration (ECA0.50) value (0.19 ± 0.02 mg/ml and 0.14 ± 0.02 mg/ml, respectively) of CUPRAC. Pearson's correlation test and principal component analysis showed the relation between TPC and various antioxidant activity assays of seaweed extracts. The seaweed methanolic extracts showed a comparatively higher zone of inhibition against all the bacterial strains than other solvent extracts. However, all the solvent extracts of U. lactuca were almost inactive against all the bacterial strains. The results of this study demonstrated that methanolic extracts of brown seaweeds showed comparatively better antioxidant and antibacterial activity, which could be used in the food and pharmaceutical applications.

Extension of shelf life of Nile tilapia (Oreochromis niloticus) fillets using seaweed extracts during refrigerated storage.

The effects of seaweed (Padina tetrastromatica, Sargassum natans, and Sargassum fluitans) ethanolic extracts on the quality and shelf life extension of Nile tilapia (Oreochromis niloticus) fillets were investigated during refrigerated storage for 20 days. Each of the seaweed ethanolic extracts solution (2%, w/v) was used for dipping the fish fillets for 10 min at 4°C. The control and seaweed extract-treated fillets were stored at 4 ± 1°C in air-tight polyethylene bags, and chemical, bacteriological, and sensory evaluation were performed at every 4 days' intervals. During the storage period, P. tetrastromatica extract significantly (p < .05) reduced the increment of pH, peroxide value, thiobarbituric acid reactive substances, and total volatile basic nitrogen values in Nile tilapia fillets compared to other seaweed extracts-treated and untreated fillets. The maximal total viable count of control, P. tetrastromatica, S. natans, and S. fluitans extracts-treated fillets was 6.53, 7.11, 6.75, and 7.10 log CFU/g at the 8th, 20th, 12th, and 16th days of storage, respectively. The total psychrotrophic count of control and seaweed extracts-treated fillets was also significantly increased (p < .05) throughout the storage period. The P. tetrastromatica extracts-treated fillets showed better sensory characteristics than other seaweed extracts-treated and control fillets. Results of this study suggest that ethanolic extracts (2%, w/v) of P. tetrastromatica extend the shelf life for 12 days longer than the control fillets in refrigerated conditions.

DYNAMICS AND MANAGEMENT OF PELAGIC SARGASSUM SPP. IN THE MEXICAN CARIBBEAN

Sargassum fluitans and S. natans (sargasso) are species of brown floating algae. They are found in the Atlantic, concentrated the Sargasso Sea, and also, since 2011, in the Great Altantic Sargassum Belt (Wang et al., 2019). Floating masses of sargasso offer resting, reproduction and feeding areas for many species (some of economic interest), and serve as a biological connectivity vector. However, since late 2014, massive quantities of sargasso have appeared on the coasts of the Mexican Caribbean. This has brought serious negative impacts, such as mortality of nearshore benthic flora and fauna, beach erosion, pollution, a decrease in tourism and high costs in managing the impacts (Chavez et al., 2020). Depending on hydrodynamic conditions, sargasso is transported to the coasts (beaching) or remains offshore, carried away by the ocean currents of the Atlantic. One of the main challenges in understanding sargasso dynamics has been the unpredictability of the influx, as sargasso concentrations in the ocean vary seasonally and interannually, and the ocean concentrations of sargasso and the beached biomass do not always coincide. Field observations, satellite imaginary analysis and numerical modelling have been used in various studies to understand the dynamics of sargasso.

Physico- and biochemical properties of alginates extracted from Ecklonia maxima and Sargassum fluitans using a simple cascade process

Physico- and biochemical properties of alginates extracted from Ecklonia maxima and Sargassum fluitans using a simple cascade process

Isotopic niche shift in the sea urchins Echinometra lucunter and E. viridis after massive arrivals of Sargassum in the Mexican Caribbean

In the Mexican Caribbean, the decomposition of unusual amounts of Sargassum (Sargassum fluitans and S. natans) has caused changes in the benthic community. The aim of this study was to evaluate the impact of massive pelagic Sargassum arrivals on the trophic structure of sea urchins Echinometra lucunter and E. viridis, using stable isotopes of carbon (δ13C) and nitrogen (δ15N) to identify variations in relative proportions of assimilated primary producers in two reef lagoons (Xahuayxol and Xcalak) in the southern Mexican Caribbean. The survey considered two scenarios: (1) with massive Sargassum arrivals (WIMA) in 2018 and (2) without massive Sargassum arrivals (WOMA) in 2017. Results revealed a decreased in δ15N and δ13C values during WIMA in primary producers and sea urchins. Furthermore, the isotopic mixing models (MixSIAR) indicated that both E. lucunter and E. viridis preferably consumed Halimeda spp. and Thalassia testudinum. The isotopic niche width obtained from Stable Isotope Bayesian Ellipses in R (SIBER) analysis showed differences between species and localities. In Xahuayxol during WIMA the corrected standard ellipse area (SEAc) of E. lucunter increased while that of E. viridis decreased. However, the latter species had a significant increase in trophic level. In Xcalak during WIMA, for both sea urchins, the SEAc increased and overlapped while the trophic levels increased significantly. Results suggest that E. viridis in Xahuayxol was better adapted to changes in resource availability, while the niche expansion of E. lucunter in Xahuayxol and E. lucunter and E. viridis in Xcalak suggest that sea urchins exhibited a starvation stage due to a decrease in food resources.

Invasive biomass algae valorization: Assessment of the viability of Sargassum seaweed as pozzolanic material

The present study aims to develop the operating conditions to produce ash from marine biomass i.e. Sargassum seaweed in order to consider their ash as pozzolanic materials. An experimental design is used to determine the most significant parameters of the ash elaboration. The parameters of the experimental design are calcination temperature (600 and 700 °C), granulometry of raw biomass (diameter D < 0.4 mm and 0.4 mm < D < 1 mm) and content by mass of algae (67 wt% of Sargassum fluitans and 100 wt% of Sargassum fluitans). The influence of these parameters on the yield of calcination, specific density, loss on ignition of ash and pozzolanic activity of ash are studied. At the same time, texture and a number of oxides in ash are observed by scanning electron microscopy. The first results show that in order to obtain light ash, a mixture of Sargassum (67% by mass of Sargassum fluitans + 33% by mass of Sargassum natans) of diameter (0.4 mm < diameter <1 mm) should be burnt at 600 °C for 3 h. In the second part, it appears that the morphological and thermal degradation characteristics of the Sargassum algae ash are similar to pozzolanic materials ones. Nevertheless, Chapelle tests, chemical composition and structural surface, crystallinity show that the Sargassum algae ash is not a pozzolanic-like material.

Variability in growth and tissue composition (CNP, natural isotopes) of the three morphotypes of holopelagic Sargassum

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.