Phycology

Microalgae represent a valuable renewable resource for biofuel production due to their high lipid content, rapid growth rates, and non-competition with food resources. Both freshwater species like Chlorella and marine species such as Dunaliella, Tetraselmis, and Nannochloropsis are among the most commonly utilized candidates. This review provides a comprehensive overview of current cultivation and harvesting methodologies for microalgae in the context of biofuel production, emphasizing sustainable aviation fuel and biohydrogen. It synthesizes recent findings, technological advancements, and practical implementations to enhance the productive and economic viability of microalgae-based biofuels, highlighting their potential as a sustainable renewable energy source. Among the biofuels, sustainable aviation fuel and biohydrogen stand out as significant contributors to reducing greenhouse gas emissions. Technologies such as the oil-to-jet process and Fischer–Tropsch synthesis are being optimized to convert algal lipids into high-quality fuels. Biohydrogen offers several advantages, including the potential for negative CO₂ emissions and compatibility with existing hydrogen infrastructure. Despite the challenges associated with the high costs of cultivation and processing, advances in biotechnological methods and process engineering promise to overcome these barriers. This review highlights the importance of continued research and development to maximize the potential of microalgal biofuels in achieving sustainable energy goals and contributing to global efforts in mitigating climate change. Full article

Codium tomentosum holds a variety of bioactive compounds, high nutritional value and health benefits, which makes it a valuable natural resource for the food, cosmetic and pharmaceutical industries. Currently, C. tomentosum is farmed at a small-scale targeting niche markets, and further expansion of production is limited by a lack of optimised propagation and cultivation methods. This study aims to identify the conditions required to control key production parameters including gametogenesis, gamete release and suitable culture conditions for the early stages of development of C. tomentosum. Wild specimens of C. tomentosum were collected on the Aguçadoura shore, north of Portugal. Gametogenesis was successfully induced in infertile specimens cultured under a short-day photoperiod (8 h:16 h; L:D). Gamete release was optimised through a combination of hydric shock and ultrasounds, with the highest gamete yield obtained after a 2 h 30 min desiccation period, followed by re-hydration and a series of three ultrasounds. Germlings, precursors of the adult C. tomentosum, grew faster when cultured under a lower light intensity (20 μmol m⁻² s⁻¹) compared to higher intensities (40 and 60 μmol m⁻² s⁻¹) in every light spectrum; additionally, the growth of germlings exposed to the lowest light intensity was significantly higher under white, red and green light spectra compared to blue light. The results on key production parameters constitute an important contribution to the establishment of nursery protocols based on sexual reproduction for aquaculture of the species. Full article

The growing interest in microalgae is driven by their potential in various bioindustries, such as biofuel production, bioremediation, and the generation of high-value biomolecules. This paper aims to systematically review the state of research on bioprospecting microalgae, their applications, and recognize trends. This study employs an exploratory and descriptive research approach, using bibliometric methods to analyze scientific production and identify emerging trends in bioprospecting microalgae research. The analysis reveals exponential publication growth, with multidisciplinary sources indicating a strong applied focus. Leading countries in this research field benefit from clear technology transfer policies, and the prevalent terms “production” and “biomass” underscore the industrial relevance. Key research areas include biofuels and bioremediation, with a combined emphasis that is often studied in cultivation and biomass production. Bioactive compounds derived from microalgae are a current trend for industrial, medical, and food applications. Although the potential for CO₂ capture is acknowledged, direct studies are limited. This systematic review provides a comprehensive overview of current trends and identifies opportunities and challenges in microalgae research, highlighting its significance for sustainable development and industrial applications. Full article

Climate change and nutrient enrichment are increasing the frequency of algal blooms, with sometimes significant impacts on coastal ecosystems. Haslea ostrearia blooms have been documented in oyster ponds and are not harmful, yet their effects in open environments remain underexplored. Marennine, a blue pigment produced by H. ostrearia, can display a range of biological properties in laboratory conditions, including antibacterial and allelopathic properties. Other blue Haslea species, forming blooms, synthesize bioactive marennine-like pigments. This study aims to understand if and how these blooms could affect the underlying community of microorganisms living in the biofilms. Morphological and molecular techniques were used to assess community dynamics during bloom events. Our findings indicate that blue Haslea blooms do not significantly alter the diatom or bacterial populations. However, they are paired with enhanced alpha diversity in the microbial communities. These observations suggest a complex interaction between bloom events and microbial dynamics. Additionally, this study expands our understanding of the bioactive properties of marennine-like pigments and their ecological roles, suggesting new avenues for biotechnological applications. This work underscores the importance of further research into the environmental and biological implications of blue Haslea blooms. Full article

The global seaweed market is expected to reach USD 17.8 billion by 2032, fuelled by growing demand for sustainable and healthy food solutions and expanding applications in agriculture and aquaculture. However, this rapid growth poses significant challenges, particularly in managing diseases that often establish themselves in intensive macroalgal culture facilities. Red rot disease, Olpidiopsis, and green spot disease often affect marine macroalgae species of high commercial interest, as seen in Pyropia/Porphyra as has already happened for “ice-ice” malaise on Kappaphycus, causing huge economic losses. These diseases are caused by infectious agents that find their place in extreme environmental conditions, such as those characterized by sudden changes in temperature and pollution. Despite technological advances aimed at monitoring the well-being of cultivated seaweed, discrepancies between regions’ technological capabilities and species vulnerability exacerbate management difficulties. This review provides an overview of diseases prevalent among marine algae, their impact on aquaculture, and the effectiveness of currently adopted treatments. This study highlights the need to improve disease management strategies and highlights the importance of understanding host–pathogen interactions in order to mitigate future epidemics. Full article

Kelp forests are facing a global decline due to climate change and human-induced stressors, underlining the urgency for proactive interventions. Among the most used restoration methods, “green gravel” has emerged as a promising solution for the recovery of degraded kelp forests. While initial findings suggest its potential effectiveness, green gravel remains a novel approach that requires fine-tuned protocols and optimisation across all stages of the process. In this study, we assessed the performance of two different seeding densities for kelp growth on green gravel to optimise the use of seeding material. Our results show that, while the juveniles in the high-density treatment grew faster, they also had a higher mortality rate during green gravel production. This was a hypothesised outcome, as growing sporophytes reared under laboratory conditions allows for faster production of a large number of individuals, increasing competition for space, which may drive higher mortality rates. Comprehensive experimentation is essential to unlock the full potential of green gravel and ensure its efficiency in all process steps, to achieve successful kelp forest restoration. Well-defined and optimised protocols are indispensable for minimising production costs, simplifying logistics, and allowing future efforts to scale up. Full article

The state of Espírito Santo has one of the greatest diversities of macroalgae along the Brazilian coast. Beach-cast seaweeds are a frequent phenomenon and exhibit great diversity. This study assessed stranded macroalgae’s composition and reproductive status to evaluate their potential for sustainable use by the local community. Monthly collections were carried out from March to November 2022, covering the rainy and dry seasons, on five beaches in Espírito Santo: three in the north and two in the south. At each beach, two 50 m transects were set up parallel to the coastline over the stranded algae patches, one near the wave-breaking zone during low tide and another around high tide, and three 1 × 1 m quadrants were randomly selected in each transect. All material within each quadrant was collected, resulting in six samples per beach. We identified 81 taxa, including 54 Rhodophyta, 16 Ulvophyceae and 11 Phaeophyceae. The taxon composition was relatively consistent across the studied regions, with the rainy season exhibiting the greatest species richness. Seventeen of the identified taxa had reproductive structures, although only four consistently presented these structures. Our results suggest that removing stranded macroalgae does not significantly impact their role as propagule sources. Full article

While molecular methods have begun to transform ecology, most algal biodiversity is still studied using the classical approach of identifying microalgae by light microscopy directly in sample material or using cultures. In this study, we compare both approaches (light microscopy and metagenomics as a molecular approach) using the freshwater ponds of the Eifel National Park in Germany as a case study. The ponds were found to be rich in desmids by light microscopy. A total of 299 species representing 81 genera were identified by light microscopy. While the molecular method does not currently allow species identification in most cases, we were able to identify 207 different algal genera. In total, 157 genera were detected only by metagenomics, 50 genera were found with both methods, and 31 genera were found by light microscopy, highlighting the need to continue using light microscopy in addition to a molecular approach. The metagenomics method has several advantages over the light microscopy method: (1) deeper assessment of alpha biodiversity, (2) better abundance numbers, and (3) complete coverage of all living matter. The latter is also a significant improvement over metabarcoding, as universal PCR primers are not available. Full article

Macroalgae are a natural oceanic resource of inexhaustible abundance for the biomass energy industry with growth rates that are three to four times greater than those of terrestrial plants. The objective of this study was to evaluate the sustainability of macroalgae as biomass for biorefining through two investigations. Firstly, the deposition of macroalgae was sampled through 28 collections on seven beaches in the city of Maceió, Brazil, over a two-year period using a zigzag sampling method, covering a deposition area of 135,000 m². From this, it was estimated that daily collection would yield 5.03 t/ha of dry biomass. Secondly, the calorific values of macroalgal biomass energy and pellet compounds were calculated. The lower calorific value (8.82 MJ/kg) found from a compound of 13 species analyzed was similar to that of the main biomass used in Brazil to obtain energy, i.e., sugarcane bagasse, which has been evaluated as 8.91 MJ/kg. Macroalgal biomass in the form of condensed energy pellets was found to have a higher calorific value of 20.18 MJ/kg, i.e., 1.2% greater than the average for terrestrial biomass pellets. Based on the results obtained, it was observed that macroalgal biomass has the possibility of becoming a new renewable feedstock with potential for bioenergy. The estimates for the deposition of biomass show possibilities for producing biofuels from marine algal raw material, which provides scope for creating another sustainable alternative for global energy issues with a reduction in environmental problems. Full article

For over a decade, numerous Greater Caribbean and Western African coasts have received enormous masses of holopelagic Sargassum spp. (sargasso). A promising use of this beached biomass as a feed ingredient in the animal industry is restricted by its high arsenic (As) content. This proof of concept aimed to demonstrate that simple, low-cost processes involving hot water (either fresh or seawater) and/or citric acid can remove arsenic from the sargasso. Sargasso collected from a Mexican Caribbean beach in December 2023 had a total arsenic level of 62.2 mg/kg, which decreased to 7.2 mg/kg after treatment with hot freshwater (90 °C for 15 min), and then further decreased to 0.8 mg/kg when followed up with a citric acid treatment. Sargasso collected in March 2024 had total arsenic of 89 mg/kg, which was lowered to 2.6 mg/kg by applying hot freshwater and citric acid sequentially. Employing only citric acid reduced the arsenic concentration to 8.0 mg/kg, while treating the sargasso only with hot seawater reduced the As level to 10.1 mg/kg. Thus, simply using hot water, either fresh or seawater, lowered the arsenic levels to acceptable levels for the animal feeding sector. These straightforward and potentially cost-effective methods may transform the restraint of high arsenic contents into a valuable opportunity to use these seaweeds as animal feed. Full article

Recent interest in scaling commercial kelp industries in Western cultures is juxtaposed by the apparent challenges in achieving more consistent and predictable yields. As such, site-level factors are a dominant and recurring conversation amongst stakeholders. The availability of seawater nitrogen (nitrate, ammonium, total N) can be highly variable across space and time and is often one of the top concerns for site selection and permitting. This study questions the relative importance of nitrogen availability on the yield of Saccharina latissima (sugar kelp) across five commercial farms on the U.S. East and West Coasts over two seasons, highlighting the relative influence of other interacting factors (i.e., farm design). We hypothesized that nitrate would strongly correlate with the harvested yield. Our results show significant spatial and annual variability in the kelp yield and ambient nutrients across and within farms, but with weak covariance. Standard linear regression suggests that seawater nitrogen is a poor explanatory factor for kelp yield, explaining 11.0% of the variation around the mean compared to the line spacing (explaining 26.1%) and the interaction between the total N and the line spacing (explaining 50.0%). Quartile regression, however, suggests that total N alone, is the strongest predictor of a lower threshold in terms of the yield (0.10 quartile, r² = 0.431) relative to the median (0.50 quartile, r² 0.081). As such, seawater nitrogen may be a more useful metric in predicting baseline kelp yields rather than realized yields, and production above that baseline is likely more dependent on other factors that may or may not interact with seawater nitrogen. Full article

Taxonomy—the classification of species—is an important branch of biology that allows us to systematically understand and study biodiversity. Conventional taxonomy relies heavily on morphological and anatomical structures for classification, but recent discoveries of potentially cryptic species and morphological plasticity in many species underscore the importance of having an alternative or complementary method for species classification. In this paper, we discuss the emerging method of classification using biochemical signals, i.e., chemotaxonomy. We also present a case study on the feasibility of biomarker-based chemotaxonomy on the marine red alga Laurencia snackeyi using halogenated snyderane-type sesquiterpenes, which were proposed in earlier studies. Full article

The specific identification of three major morphotypes of the tropical holopelagic Sargassum species causing massive strandings on the African and Caribbean coastlines was attempted by morphological characterisation as well as quantitative and qualitative analyses of several metabolites. Of the 25 morphological variables studied on 208 samples from the North Atlantic Ocean, 22 were used to establish a dichotomous identification key, allowing without any doubt the identification of each morphotype based on their morphological criteria alone. We also attempted to differentiate morphotypes using chemical fingerprintings (HR-MAS NMR) and markers by analysing pigment level and composition using High Pressure Liquid Chromatography, terpene profiles by Thin Layer Chromatography, phenolic compound levels by the Folin-Ciocalteu assay and structures by 2D Nuclear Magnetic Resonance spectroscopy, and fatty acid composition by Gas Chromatography. While pigment level and composition, terpene profiles, and phenolic contents were not discriminating, quantification of eight fatty acids enabled the differentiation of the three morphotypes. Furthermore, phlorotannin purification permitted their structural characterisation allowing discrimination between the three morphotypes. Our study highlights the potential of the free fatty acid profile and phlorotannin structure as good chemomarkers in order to discriminate between the three morphotypes of holopelagic Sargassum. Full article

Brining and dry salting are traditional preservation techniques used to extend the shelf life of foods including seaweeds. In this study, brining (40% NaCl solution weight/volume) and dry salting (30% weight/weight) processes were applied to fresh kelp to achieve a target water activity of less than 0.77, and the effect of salting treatment on consumer acceptance was assessed. The processed samples were stored at 4 °C for 2 weeks until the sensory analysis. Processed kelp samples were used as the primary ingredient in a salad with shredded carrots and sesame dressing. Three salad samples (salad with fresh kelp (control), brined, or dry salted sugar kelp) were presented to the panelists to assess the liking of sensory attributes including salt intensity, color, aroma, flavor, texture, and overall liking. Significant differences in the liking of flavor and texture were observed, with consumers rating both treatments made with salted seaweed higher than a salad made from fresh seaweed. Panelists identified the availability and lack of information regarding nutritional benefits as barriers to their seaweed consumption. These results indicate that in addition to extending shelf life, the preservation of kelp by salting may increase consumer acceptability. Full article

This parametric study aimed to analyze the effects of increased magnetic field exposure (MFE) on the growth and production of the bioactive compounds of Chlorella (C.) vulgaris. With the intent of studying the effect of an increased MFE, the magnetic field typically experienced by life on Earth was amplified by an order of magnitude. In the increased-MFE environment, six treatments of C. vulgaris with two repetitions for each treatment were exposed to a magnetic field of 5 Gauss (500 µT) about each axis, which was generated in a state-of-the-art Helmholtz cage. The treatments and the control were characterized by the duration of exposure, which was varied from 0 min to 120 min with a step increment of 20 min. The treatments were repeated for six days (TR1) and twelve days (TR2) in two separate experiments. From the first day of the treatment, the specimens in both the experiments were propagated for twenty-one days. For parametric analysis, the overall growth, protein, and beta-carotene content were measured every three days for twenty-one days. For TR1 in general, the samples treated with the increased MFE demonstrated a higher growth rate than the control. Specifically, for the specimen treated with 40 min of the increased MFE, the growth on the 21st day was measured to be 38% higher than the control. For the specimen treated with 120 min of the increased MFE, the protein content on the 15th day was measured to be 15.6% higher than the control. For the specimen treated with 40 min of the increased MFE, the beta-carotene content on the 15th day was measured to be 20.4% higher than the control. For TR2 in general, the results were inferior compared to TR1 but showed higher production than the control specimen. Specifically, for the specimen treated with 80 min of the increased MFE, the protein content on the 21st day was measured to be 4.3% higher than the control. For the specimen treated with 100 min of the increased MFE, the beta-carotene content on the 15th day was measured to be 17.1% higher than the control. For the specimen treated with 100 min of the increased MFE, the growth on the 21st day was measured to be 5% higher than the control. Overall, the treated specimens in TR1 exhibited significantly higher production compared to the control specimen. The treated specimen in TR2 demonstrated some adverse impacts, but still exhibited higher production compared to the control specimen. Full article

The term ‘cosmeceutical’ refers to cosmetic products that offer medicinal or drug-like benefits. Marine algae are rich sources of bioactive compounds, particularly carbohydrates and peptides, which have gained attention for their potential in cosmeceuticals. These compounds are abundant, safe, and have minimal cytotoxicity effects. They offer various benefits to the skin, including addressing rashes, pigmentation, aging, and cancer. Additionally, they exhibit properties such as antimicrobial, skin-whitening, anti-aging, antioxidant, and anti-melanogenic effects. This review surveys the literature on the cosmeceutical potentials of algae-derived compounds, focusing on their roles in skin whitening, anti-aging, anticancer, antioxidant, anti-inflammatory, and antimicrobial applications. The discussion also includes current challenges and future opportunities for using algae for cosmeceutical purposes. Full article

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. Full article

Pelagic Sargassum landings (hereby referred to as sargasso) increased dramatically in 2011 throughout the equatorial tropical Atlantic due to the formation of the Great Atlantic Sargassum Belt (GASB). Despite increasing reports, understanding of local abundances and vegetative characteristics, especially in South Florida, remains limited. From 2018 to 2021, sargasso was collected at two South Florida beaches, with additional sampling at a third beach to assess nutrient and heavy metal concentrations. Biomass landings varied greatly, with S. fluitans III predominant during the “peak season” (May to July) and S. natans I predominant in the “off season”, while S. natans VIII was consistently least abundant. This suggests that South Florida may receive sargasso from the Sargasso Sea during the low season and from the GASB during the peak sargasso season. Across all three morphotypes, mean nitrogen (N) and phosphorus (P) contents were 0.97% and 0.04% (dry weight), respectively. Out of the 16 heavy metals detected, our values were similar to those reported across the Caribbean. Arsenic was the most prevalent heavy metal, with sargasso containing epibionts having higher arsenic concentrations. These results provide comprehensive information to better understand the characteristics and potential origin of sargasso landings in South Florida. Full article

Core chlorophytes possess glycerol-3-phosphate dehydrogenases (GPDs) with an unusual bidomain structure, consisting of a glycerol-3-phosphate phosphatase (GPP) domain fused to canonical GPD domains. These plastid-localized enzymes have been implicated in stress responses, being required for the synthesis of glycerol under high salinity and triacylglycerols under nutrient deprivation. However, their regulation under varying environmental conditions is poorly understood. C. reinhardtii transgenic strains expressing constitutively bidomain GPD2 did not accumulate glycerol or triacylglycerols in the absence of any environmental stress. Although the glycerol contents of both wild type and transgenic strains increased significantly upon exposure to high salinity, cycloheximide, an inhibitor of cytoplasmic protein synthesis, abolished this response in the wild type. In contrast, GPD2 transgenic strains were still capable of glycerol accumulation when cultured in medium containing cycloheximide and NaCl. Thus, the pre-existing GPD2 protein appears to become activated for glycerol synthesis upon salt stress. Interestingly, staurosporine, a non-specific inhibitor of protein kinases, prevented this post-translational GPD2 protein activation. Structural modeling analyses suggested that substantial conformational rearrangements, possibly triggered by high salinity, may characterize an active GPD2 GPP domain. Understanding this mechanism(s) may provide insights into the rapid acclimation responses of microalgae to osmotic/salinity stress. Full article