Biomass composition of the golden tide pelagic seaweeds Sargassum fluitans and S. natans (morphotypes I and VIII) to inform valorisation pathways

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.

Adaptation of a microbial consortium to pelagic Sargassum modifies its taxonomic and functional profile that improves biomethane potential

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation is a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum. Microbial adaptation was performed in a fed-batch mode for 100 days by progressive feeding of Sargassum. The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of predicted genes related to different metabolic functions was affected during the adaptation stage when Sargassum concentration was increased. At the end of the adaptation stage, the abundance of the predicted genes increased again. The adapted microbial consortium demonstrated a 60% increase in both biomethane potential and biodegradability index. This work offers valuable insights into the development of treatment technologies and the effective management of pelagic Sargassum in coastal regions, emphasizing the importance of microbial adaptation in this context.

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.

The Use of Sargassum spp. Ashes Like a Raw Material for Mortar Production: Composite Performance and Environmental Outlook

The accumulation of brown algae from the genus Sargassum has been increasing over the years in coastal regions of the Caribbean, Africa, Brazil, and Mexico. This causes harmful effects to the ecosystem, human health, the economy, and the climate due to gas emissions from its decomposition process. There is the possibility of this biomass being reused in civil construction, and some studies have been carried out on its application to common Portland cement mortar. As such, the objective of this study is to evaluate the potential of sargassum ash as a mineral addition to partially replace fine aggregates in Portland cement mortar. Characterization of the raw materials was carried out through X-ray fluorescence spectroscopy, loss on ignition, particle size distribution, Brunauer-Emmett-Teller (BET) analysis, real density, X-ray diffraction, scanning electron microscopy, and dispersion spectroscopy of electrons. The mortars were prepared by partially replacing the fine aggregate (sand) with sargassum ash at 0%, 5%, 10%, and 20%. Mortar performance was evaluated through water absorption, apparent porosity, apparent specific mass, and compressive strength 7, 28, and 63 days after curing. Lastly, a life cycle assessment was conducted in accordance with ISO standards 14040:2006 and 14044:2006. The results showed that replacing sand with sargassum ash increases water absorption and apparent porosity, and decreases the apparent specific mass and compressive strength as replacement increases. Nevertheless, the compressive strength results after 63 days for 5 and 10% replacement did not differ statistically from reference values. The life cycle assessment indicated that mortars with partial replacement of sand by sargassum ash show positive environmental impacts when compared to reference values for most categories, regardless of the scenario analyzed, especially for mortar with 10% replacement. As such, the use of sargassum ash at 10% does not alter the mortar's compressive strength values after 63 days, but does reduce its environmental impact. The application of this biomass in civil construction materials provides a destination for this algae, and that can be a solution to mitigate the social, environmental, and economic problems it has been causing.

Distinct bacterial succession and functional response to alginate in the South, Equatorial, and North Pacific Ocean

The availability of alginate, an abundant macroalgal polysaccharide, induces compositional and functional responses among marine microbes, but these dynamics have not been characterized across the Pacific Ocean. We investigated alginate-induced compositional and functional shifts (e.g., heterotrophic production, glucose turnover, hydrolytic enzyme activities) of microbial communities in the South Subtropical, Equatorial, and Polar Frontal North Pacific in mesocosms. We observed that shifts in response to alginate were site-specific. In the South Subtropical Pacific, prokaryotic cell counts, glucose turnover, and peptidase activities changed the most with alginate addition, along with the enrichment of the widest range of particle-associated taxa (161 amplicon sequence variants; ASVs) belonging to Alteromonadaceae, Rhodobacteraceae, Phormidiaceae, and Pseudoalteromonadaceae. Some of these taxa were detected at other sites but only enriched in the South Pacific. In the Equatorial Pacific, glucose turnover and heterotrophic prokaryotic production increased most rapidly; a single Alteromonas taxon dominated (60% of the community) but remained low (<2%) elsewhere. In the North Pacific, the particle-associated community response to alginate was gradual, with a more limited range of alginate-enriched taxa (82 ASVs). Thus, alginate-related ecological and biogeochemical shifts depend on a combination of factors that include the ability to utilize alginate, environmental conditions, and microbial interactions.

Innovative spectral characterisation of beached pelagic sargassum towards remote estimation of biochemical and phenotypic properties

In recent years, pelagic sargassum (S. fluitans and S. natans - henceforth sargassum) macroalgal blooms have become more frequent and larger with higher biomass in the Tropical Atlantic region. They have environmental and socio-economic impacts, particularly on coastal ecosystems, tourism, fisheries and aquaculture industries, and on public health. Despite these challenges, sargassum biomass has the potential to offer commercial opportunities in the blue economy, although, it is reliant on key chemical and physical characteristics of the sargassum for specific use. In this study, we aim to utilise remotely sensed spectral profiles to determine species/morphotypes at different decomposition stages and their biochemical composition to support monitoring and valorisation of sargassum. For this, we undertook dedicated field campaigns in Barbados and Ghana to collect, for the first time, in situ spectral measurements between 350 and 2500 nm using a Spectra Vista Corp (SVC) HR-1024i field spectrometer of pelagic sargassum stranded biomass. The spectral measurements were complemented by uncrewed aerial system surveys using a DJI Phantom 4 drone and a DJI P4 multispectral instrument. Using the ground and airborne datasets this research developed an operational framework for remote detection of beached sargassum; and created spectral profiles of species/morphotypes and decomposition maps to infer biochemical composition. We were able to identify some key spectral regions, including a consistent absorption feature (920-1080 nm) found in all of the sargassum morphotype spectral profiles; we also observed distinction between fresh and recently beached sargassum particularly around 900-1000 nm. This work can support pelagic sargassum management and contribute to effective utilisation of the sargassum biomass to ultimately alleviate some of the socio-economic impacts associated with this emerging environmental challenge.

Microbial communities present in Sargassum spp. leachates from the Mexican Caribbean which are involved in their degradation in the environment, a tool to tackle the problem

The Sargassum phenomenon is currently affecting the Caribbean in several ways; one of them is the increase of greenhouse gases due to the decomposition process of this macroalgae; these processes also produce large amounts of pollutant leachates, in which several microbial communities are involved. To understand these processes, we conducted a 150-day study on the Sargassum spp environmental degradation under outdoor conditions, during which leachates were collected at 0, 30, 90, and 150 days. Subsequently, a metagenomic study of the microorganisms found in the leachates was carried out, in which changes in the microbial community were observed over time. The results showed that anaerobic bacterial genera such as Thermofilum and Methanopyrus were predominant at the beginning of this study (0 and 30 days), degrading sugars of sulfur polymers such as fucoidan, but throughout the experiment, the microbial communities were changed also, with the genera Fischerella and Dolichospermum being the most predominant at days 90 and 150, respectively. A principal component analysis (PCA) indicated, with 94% variance, that genera were positively correlated at 30 and 90 days, but not with initial populations, indicating changes in community structure due to sargassum degradation were present. Finally, at 150 days, the leachate volume decreased by almost 50% and there was a higher abundance of the genera Desulfobacter and Dolichospemum. This is the first work carried out to understand the degradation of Sargassum spp, which will serve, together with other works, to understand and provide a solution to this serious environmental problem in the Caribbean.

Predominant heterotrophic diazotrophic bacteria are involved in Sargassum proliferation in the Great Atlantic Sargassum Belt

Since 2011, the Caribbean coasts have been subject to episodic influxes of floating Sargassum seaweed of unprecedented magnitude originating from a new area "the Great Atlantic Sargassum Belt" (GASB), leading in episodic influxes and mass strandings of floating Sargassum. For the biofilm of both holopelagic and benthic Sargassum as well as in the surrounding waters, we characterized the main functional groups involved in the microbial nitrogen cycle. The abundance of genes representing nitrogen fixation (nifH), nitrification (amoA), and denitrification (nosZ) showed the predominance of diazotrophs, particularly within the GASB and the Sargasso Sea. In both location, the biofilm associated with holopelagic Sargassum harboured a more abundant proportion of diazotrophs than the surrounding water. The mean δ15N value of the GASB seaweed was very negative (-2.04‰), and lower than previously reported, reinforcing the hypothesis that the source of nitrogen comes from the nitrogen-fixing activity of diazotrophs within this new area of proliferation. Analysis of the diversity of diazotrophic communities revealed for the first time the predominance of heterotrophic diazotrophic bacteria belonging to the phylum Proteobacteria in holopelagic Sargassum biofilms. The nifH sequences belonging to Vibrio genus (Gammaproteobacteria) and Filomicrobium sp. (Alphaproteobacteria) were the most abundant and reached, respectively, up to 46.0% and 33.2% of the community. We highlighted the atmospheric origin of the nitrogen used during the growth of holopelagic Sargassum within the GASB and a contribution of heterotrophic nitrogen-fixing bacteria to a part of the Sargassum proliferation.

Assessing quality and beneficial uses of Sargassum compost

Sargassum spp. (specifically Sargassum fluitans and S. natans), one of the dominant forms of marine macroalgae (seaweed) found on the beaches of Florida, is washing up on the shores throughout the Caribbean in record quantities. Currently, a common management option is to haul and dispose of beached Sargassum in local landfills, potentially wasting a valuable renewable resource. The objective of this study was to determine whether composting represents a feasible alternative to managing Sargassum inundations through measurements and comparisons to eleven guidelines. Specifically, we assessed the characteristics of the compost [physical-chemical parameters (temperature, moisture content, pH, and conductivity), nutrient ratios (C:N), elemental composition, bacteria levels, and ability to sustain plant growth] in both small- and large scale experiments. Results show that although nutrient concentration ratios were not within the standards outlined by the U.S. Composting Council (USCC), the Sargassum compost was able to sustain the growth of radishes (Raphanus sativus L., var. Champion). Trace metal concentrations in the compost product were within five regulatory guidelines evaluated, except for arsenic (As) (6.64-26.5 mg/kg), which exceeded one of the five (the Florida Soil Cleanup Target Level for residential use). Bacteria levels were consistent with regulatory guidelines for compost produced in large-scale outdoor experiments but not for the small-scale set conducted in enclosed tumblers. Overall results support that Sargassum compost can be beneficially used for fill and some farming applications.

Kinetics of metal and metalloid concentrations in holopelagic Sargassum reaching coastal environments

Since 2011, the Caribbean Islands have experienced unprecedented stranding of a pelagic brown macroalgae Sargassum inducing damages for coastal ecosystems and economy. This study measures the kinetics of metal trace elements (MTE) in Sargassum reaching different coastal environments. In July 2021, over a period of 25 days, fixed experimental floating cages containing the three Sargassum morphotypes (S. fluitans III and S. natans I and VIII) were placed in three different coastal habitats (coral reef, seagrass, and mangrove) in Guadeloupe (French West Indies). Evolution of biomasses and their total phenolic content of Sargassum reveals that environmental conditions of caging were stressful and end up to the death of algae. Concentrations of 19 metal(loid) trace elements were analyzed and three shapes of kinetics were identified with the MTE that either concentrate, depurate, or remains stable. In the mangrove, evolution of MTE was more rapid than the two other habitats a decrease of the As between 70 and 50 μg g-1 in the mangrove. Sargassum natans I presented a different metal composition than the two other morphotypes, with higher contents of As and Zn. All Sargassum morphotype are rapidly releasing the metal(oid)s arsenic (As) when they arrive in studied coastal habitats. In order to avoid the transfer of As from Sargassum to coastal environments, Sargassum stranding should be avoided and their valorization must take into account their As contents.

Sargassum macroalgae from Quintana Roo as raw material for the preparation of high-performance phosphate adsorbent from aqueous solutions

Currently, the large volumes of Sargassum biomass (Sgs) arriving on Caribbean coasts are a problem that must be solved quickly. One alternative is to obtain value-added products from Sgs. In this work, Sgs is demonstrated to be a high-performance Ca - bioadsorbent for phosphate removal by a heat pretreatment at 800 °C that produces biochar. According to XRD analysis, calcined Sgs (CSgs) have a composition of 43.68%, 40.51%, and 8.69% of Ca(OH)2, CaCO3, and CaO, making CSgs a promising material for phosphate removal and recovery. Results demonstrated that CSgs have a high capacity to adsorb P over a wide range of concentrations (25-1000 mg P/L). After P removal, at low P concentration, the adsorbent material is rich in apatite (Ca5(PO4)3OH), and at high P concentration, brushite (CaHPO4•2H2O) was the main P compound. The CSg reached a Qmax of 224.58 mg P/g, which is higher than other high-performance adsorbents reported in the literature. The phosphate adsorption mechanism was dominated by chemisorption, followed by precipitation according to the pseudo-second-order kinetic model. The solubility of P (74.5 wt%) in formic acid solution and the water-soluble P (24.8 wt%) for CSgs after P adsorption indicated that the final product presents the potential to be used as fertilizer for acid soils. This biomass's processability and high phosphate adsorption performance for P removal make CSgs a potential material for wastewater treatment, and subsequent use of these residues as fertilizer offers a circular economy solution to this problem.

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.

Energy-saving pretreatments affect pelagic Sargassum composition and DNA metabarcoding reveals the microbial community involved in methane yield

Sargassum spp. flood the Caribbean coastline, causing damage to the local economy and environment. Anaerobic digestion (AD) has been proposed as an attractive option for turning macroalgae into valuable resources. Sargassum spp. has a complex composition that affects the microbial composition involved in AD which generates a low methane yield. This study aimed to improve the methane yield of pelagic Sargassum, using different energy-saving pretreatments and identifying the microbial community associated with methane production. We applied different energy-saving pretreatments to algal biomass and assessed the methane yield using a biomethane potential (BMP) test. The microbial communities involved in the AD of the best- and worst-performing methanogenic systems were analyzed by high-throughput sequencing. The results showed that pretreatment modified the content of inorganic compounds, fibers, and the C:N ratio, which had a strong positive correlation with BMP. The water washing pretreatment resulted in the best methane yield, with an increase of 38%. DNA metabarcoding analysis revealed that the bacterial genera Marinilabiliaceae_uncultured, DMER64, Treponema, and Hydrogenispora, as well as the archaea genera Methanosarcina, RumEn_M2, Bathyarchaeia, and Methanomassiliicocus, dominated the microbial community with a high methane yield. This study is the first to demonstrate the microbial community structure involved in the AD of Sargassum spp. The pretreatments presented in this study can help overcome the limitations associated with methane yield.

Characterization of sargassum accumulated on Dominican beaches in 2021: Analysis of heavy, alkaline and alkaline-earth metals, proteins and fats

This paper presents the characterization of sargassum that reached the shores of eight Dominican beaches in 2021. The analysis of heavy, alkaline and alkaline-earth metals was performed by ICP-OES. Twelve heavy metals were studied, with the highest concentrations corresponding to Fe, As, and Zn. Regarding the alkaline and alkaline-earth metals, the highest concentrations were detected for Ca, K, Na and Mg. The high values of arsenic and alkali and alkaline-earth metal salts do not suggest using these algae in agriculture. It is recommended to carry out arsenic speciation studies to assess whether the form in which it is found is bioavailable for plants and animals. The heavy metal contamination index was determined, which ranged between 0.318 and 3.279. Finally, for the first time in the country, the organic fraction of sargassum was analyzed.

Effect of Pelagic Sargassum on In Vitro Dry Matter and Organic Matter Degradation, Gas Production, and Protozoa Population

This study determined the effect of pelagic Sargassum on in vitro dry matter and organic matter degradation, total gas production (TGP), and protozoa population. The treatments were different levels of Sargassum inclusion on a basal substrate (Stargrass hay; Cynodon nlemfuensis) as follows: T0 (control treatment based on Stargrass hay), T10 (90% Stargrass hay + 10% Sargassum), T20 (80% Stargrass hay + 20% Sargassum), and T30 (70% Stargrass hay + 30% Sargassum). Ruminal fermentation kinetics and protozoa population were determined during 72 h of in vitro incubations. Compared to control, dry matter degradability at 48 and 72 h and organic matter degradability at 24 and 48 h were higher in Sargassum treatments. TGP was lower with T20 at 48 h. The total population of protozoa and the concentration of Entodinium spp. were lower at T20 at 48 h and T30 at 72 h. Cl, S, Ca, K, and Zn (103, 5.97, 88.73, 285.70 g/kg, and 15,900 mg/kg) were high in Sargassum, reaching twice or even nine times higher than the contents in Stargrass (11.37, 1.60, 43.53, 87.73 g/kg, and 866.67 mg/kg). Overall, up to 30% pelagic Sargassum could be included in hay-based substrates from tropical grasses without negative effects on in vitro dry matter and organic matter degradability.

Influence of Fe2O3 Nanoparticles on the Anaerobic Digestion of Macroalgae Sargassum spp

The anaerobic digestion (AD) of biomass is a green technology with known environmental benefits for biogas generation. The biogas yield from existing substrates and the biodegradability of biomasses can be improved by conventional or novel enhancement techniques, such as the addition of iron-based nanoparticles (NPs). In this study, the effect of different concentrations of Fe2O3-based NPs on the AD of brown macroalga Sargassum spp. has been investigated by 30 days trials. The effect of NPs was evaluated at different concentrations. The control sample yielded a value of 80.25 ± 3.21 NmLCH4/gVS. When 5 mg/g substrate and 10 mg/g substrate of Fe2O3 NPs were added to the control sample, the yield increased by 24.07% and 26.97%, respectively. Instead, when 50 mg/g substrate of Fe2O3 NPs was added to the control sample, a negative effect was observed, and the biomethane yield decreased by 38.97%. Therefore, low concentrations of Fe2O3 NPs favor the AD process, whereas high concentrations have an inhibitory effect. Direct interspecies electron transfer (DIET) via Fe2O3 NPs and their insolubility play an important role in facilitating the methanogenesis process during AD.

Seasonal variation in morphotype composition of pelagic Sargassum influx events is linked to oceanic origin

The recent proliferation of pelagic Sargassum spp. in the Tropical Atlantic causes major ecological and socioeconomic impacts to the wider Caribbean when it washes ashore, with regional fisheries and tourism industries particularly affected. The Caribbean influxes have been tracked to a new bloom region known as the North Equatorial Recirculation Region (NERR) encompassing the area between the South Equatorial Current and the North Equatorial Counter Current and extending from Africa to South America. The vast biomass of Sargassum presents serious problems when it washes ashore but also represents significant commercial opportunities, especially with biofuel and fertilizer. The floating Sargassum mats are themselves diverse ecosystems that vary both in their biodiversity and biochemical attributes. Two major species (Sargassum fluitans and S. natans) have been identified as well as several distinguishable morphotypes of each. Oceanic mixing tends to blend the morphotypes together making it difficult to determine if there are regions of the NERR that favour bloom and growth of the distinct types. In this study, we quantify the species and morphotype composition of Sargassum strandings in Barbados and test if this is related to separate oceanic origins and routes travelled using a backtracking algorithm based on ocean drifter data. We found significant seasonal variation in the relative abundance of three morphotypes and this could be traced to two distinct easterly sub-origins and/or transport pathways; one area around 15° N that travels directly E-W across the Atlantic, and another area generally south of 10° N that takes a more meandering route coming close the coast of South America. These findings contribute towards our understanding of why the Tropical Atlantic bloom is presently occurring as well as towards addressing valorisation constraints surrounding variation in the supply of the three commonly occurring morphotypes.

Characterization of Sargassum spp. from the Mexican Caribbean and Its Valorization through Fermentation Process

Sargassum is a brown macroalga that has become a general environmental problem in the Mexican Caribbean. Despite the negative effects on the beaches, the algae contain compounds of biotechnological and agronomic interest. The possibility of using sargassum as a substrate under liquid media fermentation (LMF) processes will allow the obtention of bioactive compounds. In this research, five species of Sargassum from the Puerto Morelos region were collected from the beach. The samples were divided into natural Sargassum and washed Sargassum, and the total phenolic compounds (TPC), flavonoids (F), and antioxidant capacity (AOxC) were determined. Once the material was characterized, it was fermented in the LMF process using the Aspergillus niger strain, where the obtained extracts were analyzed. Three holopelagic and one benthic species were identified. The proximal analysis of the seaweed in natural and washed conditions shows adequate carbon–nitrogen ratio values for use as a substrate for microbial degradation. Comparing the fermented extracts with fresh Sargassum, the analyses showed a TPC increase for washed Sargassum fermentation and a TPC decrease for natural Sargassum fermentation; the flavonoid content reached 8-fold higher in the washed Sargassum fermentation. An average AOxC of 57% was achieved during the washed Sargassum LMF process, with a maximum of 69% of ABTS inhibition. Considering these results, Sargassum can be used as a substrate in LMF processes to obtain bioactive compounds.

Diversity of the holopelagic Sargassum microbiome from the Great Atlantic Sargassum Belt to coastal stranding locations

The holopelagic brown macroalgae Sargassum natans and Sargassum fluitans form essential habitats for attached and mobile fauna which contributes to a unique biodiversity in the Atlantic Ocean. However, holopelagic Sargassum natans (genotype I & VIII) and Sargassum fluitans (genotype III) have begun forming large accumulations with subsequent strandings on the western coast of Africa, the Caribbean and northern Brazil, threatening local biodiversity of coastal ecosystems and triggering economic losses. Moreover, stranded masses of holopelagic Sargassum may introduce or facilitate growth of bacteria that are not normally abundant in coastal regions where Sargassum is washing ashore. Hitherto, it is not clear how the holopelagic Sargassum microbiome varies across its growing biogeographic range and what factors drive the microbial composition. We determined the microbiome associated with holopelagic Sargassum from the Great Atlantic Sargassum Belt to coastal stranding sites in Mexico and Florida. We characterized the Sargassum microbiome via amplicon sequencing of the 16S V4 region hypervariable region of the rRNA gene. The microbial community of holopelagic Sargassum was mainly composed of photo(hetero)trophs, organic matter degraders and potentially pathogenic bacteria from the Pseudomonadaceae, Rhodobacteraceae and Vibrionaceae. Sargassum genotypes S. natans I, S. natans VIII and S. fluitans III contained similar microbial families, but relative abundances and diversity varied. LEfSE analyses further indicated biomarker genera that were indicative of Sargassum S. natans I/VIII and S. fluitans III. The holopelagic Sargassum microbiome showed biogeographic patterning with high relative abundances of Vibrio spp., but additional work is required to determine whether that represents health risks in coastal environments. Our study informs coastal management policy, where the adverse sanitary effects of stranded Sargassum might impact the health of coastal ecosystems.

Methane Production of Sargassum spp. Biomass from the Mexican Caribbean: Solid-Liquid Separation and Component Distribution

In the last decade, Sargassum spp. seaweed species have caused massive flooding on the Caribbean Sea coasts. These seaweed species have a high content of recalcitrant compounds, such as insoluble fibers and polyphenols, which generate low methane yields in anaerobic digestion (AD). This study investigated the effect of solid-liquid separation of Sargassum biomass on biodegradability and methane yield. A biochemical methane potential (BMP) test was conducted with both fractions and raw biomass (RB). A mass balance was developed to assess the distribution of the components. The obtained liquid fraction (LF) showed high biodegradability and a high methane production rate, and it generated a methane yield of 159.7 ± 7.1 N L kg VS-1, a value that corresponds to approximately twice that achieved with RB and the solid fraction (SF). The component distribution analysis showed that about 90% of total solids (TS), volatile solids (VS), ash, carbon, and cellulose were retained in the SF. In conclusion, the LF had high biodegradability and methane yield. This suggests the potential for LFs of Sargassum biomass to be treated in large-scale high-load reactors; however, studies applied to SFs are needed because they retain a large amount of organic matter with low biodegradability.

Trace metal content from holopelagic Sargassum spp. sampled in the tropical North Atlantic Ocean: Emphasis on spatial variation of arsenic and phosphorus

We document for the first time, the spatial distribution at basin scale (North tropical Atlantic Ocean) of As, P and trace metal (TM) concentrations in the three morphotypes belonging to the two holopelagic species Sargassum natans and S. fluitans and three morphotypes: S. natans VIII, S. natans I and S. fluitans III. These samples collected in the North equatorial current (NEC) and in the subtropical Sargasso Sea (sSS) (∼25°N, 60°W) were also compared to coastal samples collected downwind Guadeloupe Island and on the strand of Martinique (mangrove and beach). Along the studied zonal oceanic transect, the highest values of As (range 120-240 μg g-1, dry weight, dw) were found in the sSS area where primary production is highly limited by phosphorus. At these stations, the P content of Sargassum spp. was minimal (range 500-1000 μg g-1, dw) as well as the content in Cd and Zn known for their nutrient-like oceanic behaviors and distributions very similar to P. This illustrates for the first time in the natural environment, the higher bioaccumulation of arsenic in Sargassum spp. in P-limiting conditions which is due to the competition in the phosphate transporter between arsenate and phosphate. As compared to samples collected at sea, the Sargassum spp. collected in the strand of Martinique had (1) lower As concentrations (typical range 30-45 μg g-1, dw) and (2) much higher Al, Fe, Mn, Cr and Co concentrations, showing a certain ability of Sargassum spp. to be depurated of its As content in the coastal zone following competitive exchange with terrigenous metals.

Environmental impact of Sargassum spp. landings: an evaluation of leachate released from natural decomposition at Mexican Caribbean coast

Large volumes of pelagic Sargassum spp. have stranded periodically on the Mexican Caribbean shoreline. The aim of this research was to study the mobility of metals through the leachates released into the environment during the natural decomposition process of Sargassum spp. Fresh Sargassum samples were placed in cone-bed reactors: under laboratory and local environmental conditions. The leachate generated naturally by decomposition in both conditions was recovered periodically and analyses of pH, volume, and metal content were carried out. Sargassum biomass was monitored by electron microscopy, FT-IR, and CHNS analysis. The Sargassum biomass studied presented a C: N ratio of 24.39, making it a potential raw feedstock for biofuels and other value-added products. Calculations performed on leachate production allowed inferring that each ton of fresh Sargassum that decomposes at a controlled temperature of 27 °C can produce 316 L of leachate. This leachate can contain 5.67 g of As and other potentially toxic metals (e.g., B, Al, Cu). At the end of both experiments, the biomass that was incubated for 30 days presented a C: N ratio of 28.86, so it can still be used as raw material for biofuels; however, the Sargassum biomass that remained 180 days in incubation decreased its C:N ratio at 8.45 at this point, it can be considered a waste. The leachate generated during the natural decomposition process of Sargassum on beaches or disposal sites represents a high risk of contamination of the Yucatan Peninsula water system due to the high content of arsenic and the presence of potentially toxic metals.

Scavenging of select radionuclides and trace elements by pelagic Sargassum in the Caribbean Sea

In recent years, the North Atlantic and the Caribbean Sea have experienced unusual and unprecedented pelagic Sargassum blooms, which may adversely affect coastal ecosystems and productive ocean. Sargassum has the potential to scavenge trace elements and radionuclides from seawater, and when bioaccumulated and thus concentrated, can pose a potential threat to higher trophic organisms, including humans that consume impacted seafood. In this study, trace elements and naturally-occurring U/Th-series radionuclides were measured in Sargassum that were collected in the coastal waters of the Caribbean Sea (Antigua/Barbuda, Belize, and Barbados) to better define baseline concentrations and activities, and to assess the scavenging potential for these trace elements and radionuclides. The mean concentration of trace elements observed in Sargassum collected across these three Caribbean Sea are ranked accordingly to the following descending order: Sr > As>Fe > Mn > Zn > Ni > V > C > Cd > Se > Co > Cr > Pb > Ag > Hg. 210-Po and 210Pb activities in Sargassum were observed to be more elevated than previously reported values.

Metals and metalloids concentrations in three genotypes of pelagic Sargassum from the Atlantic Ocean Basin-scale

Since 2011, the Caribbean Islands have witnessed unprecedented massive stranding of a pelagic brown algal Sargassum spp. inducing damages for coastal ecosystems and economy. By accumulating heavy metals, Sargassum can play a role in contaminant transportation from offshore to the coast. In 2019, three genotypes of Sargassum (S. fluitans III, S. natans I, and VIII) were sampled in seven stations along a 3400 km transect in the Atlantic Ocean. Concentrations of 15 heavy metal(loid)s elements were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). Mean metal concentrations were ranked following descending order: As >Fe > Al > Mn > Cd > Zn > Ni > V > Cu > Cr > Hg. The metalloid As was the most abundant contaminant with a maximum value of 115 ppm, previously observed in the Caribbean area (80-150 ppm). At Atlantic Ocean Basin-scale, metallic element concentrations do not present spatial longitudinal gradients. Genotypes S. fluitans III and S. natans (I and VIII), present differents metal(loid)s contamination distinct patterns.

Pelagic Sargassum events in Jamaica: Provenance, morphotype abundance, and influence of sample processing on biochemical composition of the biomass

Pelagic Sargassum species have been known for centuries in the Sargasso Sea of the North Atlantic Ocean. In 2011, a new area concentrating high biomass of these brown algae started developing in the Tropical Atlantic Ocean. Since then, massive and recurrent Sargassum influxes have been reported in the Caribbean and off the coast of Western Africa. These Sargassum events have a major negative impact on coastal ecosystems and nearshore marine life, and affect socio-economic sectors, including public health, coastal living, tourism, fisheries, and maritime transport. Despite recent advances in the forecasting of Sargassum events, and elucidation of the seaweed composition, many knowledge gaps remain, including morphotype abundance during Sargassum events, drift of the seaweeds in the months prior to stranding, and influence of sample processing methods on biomass biochemical composition. Using seaweeds harvested on the coasts of Jamaica in summer of 2020, we observed that S. fluitans III was the most abundant morphotype at different times and sampling locations. No clear difference in the geographical origin, or provenance, of the Sargassum mats was observed. The majority of Sargassum backtracked from both north and south of Jamaica experienced ambient temperatures of around 27 °C and salinity in the range of 34-36 psu before stranding. We also showed that cheap (sun) compared to expensive (freeze) drying techniques influence the biochemical composition of biomass. Sun-drying increased the proportion of phenolic compounds, but had a deleterious impact on fucoxanthin content and on the quantities of monosaccharides, except for mannitol. Effects on the content of fucose containing sulfated polysaccharides depended on the method used for their extraction, and limited variation was observed in ash, protein, and fatty acid content within most of the sample locations investigated. These observations are important for the storage and transport of the biomass in the context of its valorisation.

In-depth study of bio-oil and biochar production from macroalgae Sargassum sp. via slow pyrolysis

Sargassum is undoubtedly one of the most predominant brown macroalgae, posing a significant disposal problem for coastal areas worldwide. The effective valorization of Sargassum sp. would be beneficial not only for environmental mitigation but also for producing high-value chemicals. However, the valorization of Sargassum sp. for bio-oil and biochar production via slow pyrolysis has not been well studied yet. Hence, this study aimed to conduct a comprehensive investigation into bio-oil and biochar production from Sargassum sp. via slow pyrolysis to provide valuable data for further valorization. A batch reactor was employed, and the pyrolysis of Sargassum sp. was conducted in a temperature range of 400-600 °C and with retention times of 10-50 min. The results showed significant compounds could be identified in bio-oil from Sargassum sp., including carboxylic acids, furan derivatives, aliphatic hydrocarbons, and N-aromatic compounds. Based on the ultimate analysis, the H/C and O/C atomic ratios of biochar were lower than the feedstock, reflecting the occurrence of dehydration and decarboxylation reactions throughout the pyrolysis. Biochar exhibited calorific values in the range of 23.12-25.89 MJ kg-1, indicating it has more potential to be used as a solid fuel than low-ranked coals. Surface morphological analysis was performed by scanning electron microscopy (SEM) and showed a larger surface area in biochar than in the algal feedstock. Furthermore, a reaction model was deduced, and it was confirmed that the pyrolysis reaction obeyed the Arrhenius behaviour. Overall, the slow pyrolysis of Sargassum sp. provides an opportunity to obtain value-added chemicals and biochars, which could be further utilized for other applications.

Trace elements in pelagic Sargassum species in the Mexican Caribbean: Identification of key variables affecting arsenic accumulation in S. fluitans

Since 2014, the Mexican Caribbean beaches have received massive influxes of the brown seaweed Sargassum (S. fluitans III, S. natans I and S. natans VIII), causing serious ecological and economic effects. Concentrations of arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) were determined over an annual cycle in pelagic Sargassum species from massive influxes into the Mexican Caribbean. The contribution of trace elements, polysaccharides (alginate and fucoidans), and their main functional groups (uronic acids and sulfate) to arsenic content in Sargassum fluitans - the most abundant species in the Sargassum influx - is discussed. Arsenic was recorded in all samples, yielding mean concentrations of 74.2 ± 2.84 mg kg-1. Significant differences were found between species for As, Cu, Fe, and Pb, but not for Cd and Zn; also, S. fluitans showed significant differences in metal content between seasons for all elements, as well as in alginate and uronic acids from fucoidan. The season of the year, copper, iron, uronic acids, and sulfate content in fucoidan were the main variables associated with arsenic accumulation in S. fluitans as evidenced with a Generalized Linear Model. Arsenic content in Sargassum biomass exceeded the maximum allowable level in the rainy season; therefore, the content of this trace element should be carefully monitored for safe usage of Sargassum biomass.

Algae application in civil construction: A review with focus on the potential uses of the pelagic Sargassum spp. biomass

Pelagic Sargassum, usually found at the Sargasso Sea and the Western portion of the North Atlantic and Gulf of Mexico, has been detected in many new locations through the tropical Atlantic. The huge biomass found from the African coast to the Caribbean was called the Great Atlantic Sargassum Belt and is responsible for the stranding of tons of algae on coastal regions. Despite the environmental, social, and economic impacts, sargassum is a valuable source for multiple uses at the industry, such as alginates, cosmetics, recycled paper and bioplastics, fertilizers, and as raw material for civil construction. This work presents a systematic literature review on the use of algae at the civil construction sector, with a focus on the valorization of the pelagic Sargassum spp. biomass, by identifying the potential applications related to the use of other algal species. The review considered other genera of marine algae and marine angiosperms, resulting in a total of 31 selected articles. The marine grass Posidonia oceanica was the most used species, found in eight published papers, followed by the red alga Kappaphycus alvarezii with four studies. Two articles were available on the use of pelagic Sargassum spp. (S. fluitans and S.natans) for construction materials (adobe and pavement), with potential good results. The literature presented results from the use of marine algae and sea grasses for particleboards, polymeric and cemented composites, adobe, pavement, facades, and roofs. This article provides a state-of-the-art review of algal application in the civil construction sector and points out the main directions for the potentialities on the insertion of the Sargassum spp. biomass into the production chain of the sector.

Species composition and chemical characterization of Sargassum influx at six different locations along the Mexican Caribbean coast

In the last decade, unprecedented arrivals of pelagic Sargassum (Sargassum influx) have been reported for the Caribbean coasts causing severe ecological and economical affectations and remarking the necessity to characterize the phenomenon. In the north coast of the Mexican Caribbean, spatial characterization of Sargassum influx was performed in terms of its abundance, species composition and chemical content using a combination of in situ sampling and remote sensing evaluations. Sargassum influx was detected within the 25 km fringe near to Quintana Roo coast in coincidence with beach-cast events during September 2018. Significant spatial variation in abundance and species composition of the stranded biomass was found for the six localities studied, which was related to the local environmental conditions. Pelagic species of Sargassum were the main component ranging from 78.1 to 99.6% of the total beach-cast (wrack) fresh biomass, whereas benthic macrophytes (seagrasses and macroalgae) were a minor component reaching up to 21% in some localities. The biochemical composition of beach-cast Sargassum resulted spatially homogeneous for most of the components analyzed; only carbon tissue content, ash metals (particularly Fe and As) and isotopic composition changed spatially. This study represents baseline information for the region. Long-term seasonal evaluations of Sargassum influx along Mexican Caribbean are required to define adequate management strategies and exploitation.

Green Synthesis of Homogeneous Gold Nanoparticles Using Sargassum spp. Extracts and Their Enhanced Catalytic Activity for Organic Dyes

Sargassum species-based extracts were used to carry out the synthesis of homogeneous gold nanoparticles. Various techniques were used to determine the characteristics and composition of the nanoparticles. The UV-Vis results showed that the 50% water/ethanol extract had the most reducing agents and stabilizers. Therefore, this type of extract was used to synthesize nanoparticles and for their subsequent characterization. Crystallinity and crystal size were evaluated using X-ray diffraction. Size and morphology were analyzed using scanning electron microscopy, showing that the gold nanoparticles were mostly spherical, with a size range of 15-30 nm. The catalytic activity of the gold nanoparticles was evaluated through the degradation of organic dyes: methylene blue, methyl orange, and methyl red. The degradation rates were different, depending on the nature of each dye, the simplest to degrade was methylene blue and methyl red was the most difficult to degrade. The results indicated that the use of Sargassum spp. for the synthesis of gold nanoparticles has potential in the remediation of water that is contaminated with organic dyes. Moreover, given the recent serious environmental and economic problems caused by the overpopulation of Sargassum spp. in the Mexican Caribbean, the findings hold promise for their practical and sustainable use in the synthesis of nanomaterials.

Brown Seaweed Sargassum siliquosum as an Intervention for Diet-Induced Obesity in Male Wistar Rats

The therapeutic potential of Sargassum siliquosum grown in Australian tropical waters was tested in a rat model of metabolic syndrome. Forty-eight male Wistar rats were divided into four groups of 12 rats and each group was fed a different diet for 16 weeks: corn starch diet (C); high-carbohydrate, high-fat diet (H) containing fructose, sucrose, saturated and trans fats; and C or H diets with 5% S. siliquosum mixed into the food from weeks 9 to 16 (CS and HS). Obesity, hypertension, dyslipidaemia, impaired glucose tolerance, fatty liver and left ventricular fibrosis developed in H rats. In HS rats, S. siliquosum decreased body weight (H, 547 ± 14; HS, 490 ± 16 g), fat mass (H, 248 ± 27; HS, 193 ± 19 g), abdominal fat deposition and liver fat vacuole size but did not reverse cardiovascular and liver effects. H rats showed marked changes in gut microbiota compared to C rats, while S. siliquosum supplementation increased gut microbiota belonging to the family Muribaculaceae. This selective increase in gut microbiota likely complements the prebiotic actions of the alginates. Thus, S. siliquosum may be a useful dietary additive to decrease abdominal and liver fat deposition.

Presence of Polyphenols Complex Aromatic “Lignin” in Sargassum spp. from Mexican Caribbean

In recent years, the massive influx of pelagic Sargassum spp. has generated great interest in the scientific community, highlighting the urgency of addressing the physiology and biochemical composition of these species. Until now, the presence of lignified cells in the tissue of Sargassum natans and Sargassum fluitans has not been reported. Although ‘‘lignin-like’’ compounds have been identified in green algae, the presence of true lignin in the Sargassum genus has not been confirmed. Our work is the first report of lignified cells forming the secondary cell wall in these Sargassum. This study used histological techniques applied to thick sections for identifying lignin-like tissues in Sargassum spp. The dyes as Safranin O and Toluidine have been used to differentiate lignin and cellulose in conducting tissue and to indicate the presence, absence, and distribution of these compounds in tissues. This work is the initial study of the cell wall heteropolymers structure and arrangement in Sargassum spp., providing insights into the unique cell wall architecture of these seaweeds.