Phycology

Macroalgal extracts are widely recognised as biostimulants that enhance crop productivity and plant growth under both optimal and stressful conditions. They offer a sustainable approach to mitigating the adverse effects of abiotic stress on crop development. This study investigates the efficacy of macroalgal-based fertilisers in enhancing tomato (Solanum lycopersicum L.) growth, yield, and fruit quality, as sustainable alternatives to chemical fertilisers. Different seaweed species (Sargassum muticum, Ulva ohnoi, Furcellaria lumbricalis, Ascophyllum nodosum, and a commercial A. nodosum extract) were evaluated as foliar treatments. The results showed that while the leaf fresh weight and chlorophyll content were not significantly affected, the fruit morphology and biochemical composition exhibited notable variations. Sargassum muticum-treated fruits displayed the highest °Brix (6.57), indicating superior sugar accumulation, while Ulva ohnoi maintained near-neutral pH levels (avg. 3.94), suggesting balanced acidity. Ascophyllum nodosum extracts induced the highest proline concentrations (peak: 63.77 µmol/g), but also caused extreme acidity (pH 1.39–2.58). Furcellaria lumbricalis enhanced the fruit size (axial length up to 41.4 mm), but reduced the pH sharply (1.69–2.13). The commercial product underperformed in regard to sugar content and flavour complexity. The integrative analysis revealed species-specific flavour profiles: Sargassum yielded sweet, mildly acidic fruits; Ascophyllum produced intensely aromatic, acidic tomatoes; and Ulva resulted in bland flavours. These findings underscore the importance of algal species and extraction methods in tailoring biofertilisers for target fruit qualities. This study advocates for the use of macroalgal fertilisers in sustainable agriculture, but highlights the need for optimised formulations to balance crop yield, taste, and stress adaptation. Full article

Microalgae are photosynthetic organisms with rapid growth and high biochemical diversity, capable of thriving in a variety of environments. Among them, dinoflagellates, particularly symbiotic species like Durusdinium glynnii, have gained attention due to their potential for biotechnological applications, especially in the production of valuable fatty acids. However, the delicate cultivation of dinoflagellates remains a challenge due to their sensitivity to shear stress and complex morphology. In this study, we evaluated the influence of inoculum percentage (10%, 25%, and 50%) on the growth performance and fatty acid profile of D. glynnii during a scale-up process from test tubes to a pilot-scale photobioreactor. Higher inoculum concentrations (50%) promoted faster acclimatization, higher specific growth rates (µ_max), and greater final biomass densities, optimizing the cultivation process. Meanwhile, lower inoculum concentrations (10%) favored the accumulation of polyunsaturated fatty acids, particularly DHA (C22:6n3), indicating a trade-off between biomass productivity and fatty acid biosynthesis. Overall, D. glynnii demonstrated robust adaptability, reinforcing its potential as a sustainable source of bioactive compounds. Further studies focusing on cellular and metabolic pathways are needed to better elucidate the mechanisms underlying lipid production and growth in this promising species. Full article

In most cases, the sizes of the daughter cells of diatoms follow the MacDonald–Pfitzer rule, whereby in many species all diatoms divide once in each generation. In contrast, there are division schemes in which the smaller or larger daughter cell is delayed in its division by one generation and therefore leads to Fibonacci growth. Several properties of diatoms, especially in chain-like colonies, that exhibit such delayed division can be modeled by Lindenmayer systems. These include, above all, the size and orientation of the diatoms. Certain sequences of properties, such as the differences in size indices of neighboring diatoms, are aperiodic and represent self-similar fractal structures. For the division schemes studied, explicit solutions can be found for the number of diatoms of a certain size in each generation. For the experimental differentiation of the division schemes in a diatom chain, in addition to the observation of the division processes over several generations, methods are available that only require the analysis of the structure of a sufficiently large sample. This includes the investigation of the differences in the sizes of neighboring diatoms, the orientations of the diatoms and the frequencies of size indices in a culture. These methods provide a toolbox for investigating diatom properties, applicable to the division models described. Additionally, a mathematical framework is presented that has the potential to be transferable to other properties and other division schemes. Full article

The growing demand for the sustainable production of high-value compounds, such as biofuels, lipids, and pigments like carotenoids and phycobilin, has become the subject of numerous investigations. Furthermore, this has led to the exploration of renewable methods utilizing microalgae as feedstock to mitigate the challenges associated with producing these valuable compounds. Nevertheless, despite the numerous advantages of microalgae, the development of a microalgal biorefinery that employs sustainable, environmentally friendly, and economically efficient technologies remains a necessity. To address this challenge, the bio-flocculation process, and more specifically self-flocculation, is presented as a cost-effective and energy-efficient solution. This method is as easy and effective as chemical flocculation, which is applied at an industrial scale; however, in contrast, it is sustainable and cost-effective as no costs are involved in the pre-treatment of the biomass for oil extraction or in the pre-treatment of the medium before it can be re-used. In addition, microalgae possess molecular tools that would allow the efficiency of these processes to be increased. In the present review, we summarize the microalgal harvesting technologies used, with a particular focus on bio- and self-flocculation processes, and identify the improvements that could be made to enhance the production of high-added-value compounds while simultaneously reducing costs in microalgae biorefineries. Full article

The separation of microalgae from a culture medium is a major cost and energy hurdle for the efficient production of algal biomass. Crossflow microfiltration has been found to be promising for the algal cell concentration process. Three algal strains with different cell sizes and morphology, namely Chlorella vulgaris, Nannochloris sp., and Scenedesmus sp., were studied. Analysis of the culture suspensions showed very different particle size distributions for the selected strains due to cell clustering. For a given membrane under the same operational conditions to achieve an equal volumetric reduction factor, Nannochloris sp., with the biggest particles and smallest cells, demonstrated the highest permeation flux, and in the same order of the particle sizes, it was followed by Chlorella vu. and Scenedesmus sp. For all the selected algal species, the highest dewatering rate (176–303 L/m²·h) was obtained by means of the membrane with the smallest pore size of 0.05 µm. Full article

Since 2011, pelagic sargassum blooms (S. fluitans and S. natans) have impacted coastal communities, aquaculture, tourism, and biodiversity across the Tropical Atlantic region. Whilst the initial event is generally attributed to an anomalous North Atlantic Oscillation (2009–2010), the drivers of sargassum movement and proliferation remain unclear. This research gap is particularly evident in West Africa, where annual and seasonal sargassum variability is under-researched, and a lack of consensus exists on seasonal and annual trends. This paper addresses these gaps by (1) providing a first attempt at characterising the seasonal and annual trends of sargassum biomass in the Eastern Tropical Atlantic, through using satellite imagery to create a time-series for 2011–2022; and (2) exploring the hypothetical drivers of movement and proliferation of sargassum for this area, through assessing its co-variation with potential drivers including atmospheric, oceanic, and policy, establishing a historical timeline of events. The time-series analysis reveals an annual biomass peak in September and a second peak between March and May. The exploration of potential drivers reveals that alongside sea surface temperature there are multiple factors that could be influencing sargassum biomass, and that further research is necessary to clarify primary and secondary drivers. The results contribute to understanding drivers, impacts, and predictions of sargassum blooms in the Eastern Tropical Atlantic. We anticipate that our findings will enable sargassum-affected areas to better anticipate the size and timing of sargassum events in West Africa and offer researchers a new perspective on possible drivers of proliferation within the wider Tropical Atlantic region. Full article

Reservoirs and downstream rivers draining Oregon’s Cascade Range provide critical water supplies for over 1.5 million residents in dozens of communities. These waters also support planktonic and benthic cyanobacteria that produce cyanotoxins that may degrade water quality for drinking, recreation, aquatic life, and other beneficial uses. This 2016–2020 survey examined the sources and transport of four cyanotoxins—microcystins, cylindrospermopsins, anatoxins, and saxitoxins—in six river systems feeding 18 drinking water treatment plants (DWTPs) in northwestern Oregon. Benthic cyanobacteria, plankton net tows, and (or) Solid-Phase Adsorption Toxin Tracking (SPATT) samples were collected from 65 sites, including tributaries, reservoirs, main stems, and sites at or upstream from DWTPs. Concentrated extracts (320 samples) were analyzed with enzyme-linked immuno-sorbent assays (ELISA), resulting in >90% detection. Benthic cyanobacteria (n = 80) mostly Nostoc, Phormidium, Microcoleus, and Oscillatoria, yielded microcystins (76% detection), cylindrospermopsins (41%), anatoxins (45%), and saxitoxins (39%). Plankton net tow samples from tributaries and main stems (n = 94) contained saxitoxins (84%), microcystins (77%), anatoxins (25%), and cylindrospermopsins (22%), revealing their transport in seston. SPATT sampler extracts (n = 146) yielded anatoxins (81%), microcystins (66%), saxitoxins (37%), and cylindrospermopsins (32%), indicating their presence dissolved in the water. Reservoir plankton net tow samples (n = 15), most often containing Dolichospermum, yielded microcystins (87%), cylindrospermopsins (73%), and anatoxins (47%), but no saxitoxins. The high detection frequencies of cyanotoxins at sites upstream from DWTP intakes, and at sites popular for recreation, where salmon and steelhead continue to exist, highlight the need for additional study on these cyanobacteria and the factors that promote production of cyanotoxins to minimize effects on humans, aquatic ecosystems, and economies. Full article

Due to the adverse effects associated with synthetic cosmetic ingredients, global demand is increasingly shifting toward natural formulations that offer diverse benefits for enhancing skin health and overall beauty. Researchers around the world are extensively exploring a variety of unique natural secondary metabolites for cosmeceutical applications. Among the potential candidates, phlorotannins derived from brown seaweeds have shown significant potential as an active ingredient in cosmeceutical applications. The notable properties associated with phlorotannins include antioxidant, anti-aging, whitening, anti-wrinkling, anti-inflammatory, and hair health and growth-promoting effects, making them valuable in cosmeceutical formulations. However, to date, only a limited number of studies have critically reviewed the cosmeceutical applications of phlorotannins, and most are outdated. Thus, in the present review, primary attention is given to the collected scientific data published after 2020 about the bioactive properties of brown seaweed phlorotannins related to cosmeceutical applications. Full article

Functional genomics is a powerful approach for uncovering molecular mechanisms underlying complex biological processes by linking genetic changes to observable phenotypes. In the context of algal symbiosis, this framework offers significant potential for advancing our understanding of the molecular interactions between marine dinoflagellates and their cnidarian hosts, such as corals—organisms that are foundational to marine ecosystems and biodiversity. As coral bleaching and reef degradation intensify due to environmental stressors, novel strategies are urgently needed to enhance the resilience of these symbiotic partnerships. This opinion piece explores emerging directions in functional genomics as applied to coral–algal symbiosis, with a focus on uncovering the molecular pathways that govern photosynthesis and stress tolerance. We discuss the challenges and opportunities in applying functional genomics to support coral health, improve ecosystem resilience, and inform biotechnological applications in agriculture and medicine. Together, these insights posit the potential for engineered symbioses as a needed focus in mitigating biodiversity loss and supporting sustainable ecosystem management in the face of accelerating environmental change. Full article

Achnanthidium minutissimum is a widely distributed benthic freshwater diatom. The alga can produce stalks that stick the cell to the surface and subsequently extracellular capsules developing into biofilms. Extracts of the diatom-associated bacterium Dyadobacter sp. 32 have been shown previously to induce stalk and capsule formation by the diatom. Here, we studied the impact of macronutrients on the generation of stalks induced by bacterial extracts with respect to the frequency of stalk generation and stalk lengths, using axenic cultures to avoid any additional impact of bacteria on the nutrient availability. We found that nitrate deprivation inhibited cell division of A. minutissimum within four days, but it did not initially affect stalk production or elongation. Silica limitation instead inhibited both stalk production and elongation. Similarly, sulfate was required for stalk formation, which was supported by the energy-dispersive X-ray spectroscopy of A. minutissimum cells showing that sulfur was abundant in the stalks. Full article

Light characteristics, including spectrum and intensity, significantly impact cyanobacterial biomass production, pigment biosynthesis, and cellular metabolism, influencing the composition of various biochemical compounds. This study aimed to investigate the effects of light-emitting diode (LED) illumination on biomass, pigment, and lipid production in the unicellular halotolerant cyanobacterium Aphanothece halophytica, cultivated in a suitable natural seawater (SNSW) medium. The results revealed that LED light outperformed fluorescent light, with blue LED light, particularly at an intensity of 60 μmol photons m⁻² s⁻¹, significantly enhancing growth, pigment synthesis, and lipid accumulation. This resulted in a maximum cell density of 68.96 ± 1.52 × 10⁶ cells mL⁻¹, a specific growth rate of 0.302 ± 0.002 day⁻¹, and a lipid productivity of 56.81 ± 0.75 mg L⁻¹ day⁻¹. White LED light produced lipids suitable for biodiesel, whereas blue, green, and red LEDs promoted the accumulation of polyunsaturated fatty acids (PUFAs), beneficial for food supplements. These findings highlight the potential of LED-based cultivation strategies for optimizing biomass and biochemical compound production in A. halophytica. Full article

Phycobiliproteins and pigments derived from cyanobacteria hold significant potential for diverse applications in the food, pharmaceutical, and chemical industries. The filamentous cyanobacterium Anabaena cylindrica serves as a valuable resource for extracting these compounds. This study develops a simplified, safe, and cost-effective extraction method that eliminates toxic solvents and minimizes processing steps. This makes the method applicable for all users and allows the easy integration of the extraction into biorefinery concepts in which the biomass is to be used as a fertilizer, for example. Utilizing salts such as ammonium sulfate and calcium chloride (15 gL⁻¹ each) enables the effective extraction of phycocyanin (PC) and allophycocyanin, achieving a PC concentration of 192.34 $\mathrm{mg}{\mathrm{g}}_{\mathrm{CDW}}^{-1}$ and 209.44 $\mathrm{mg}{\mathrm{g}}_{\mathrm{CDW}}^{-1}$, respectively. Ethanol was introduced as a less toxic alternative to methanol for pigment extraction, increasing chlorophyll a and carotenoid recovery by 21% and 37%, respectively. Full article

Seaweed is a resilient macrophytic plant thriving in intertidal zones. These are rapidly gaining attention due to their autotrophic nourishment, rapid growth, and minimal land requirement for cultivation. Seaweed is used in various food and non-food sectors, thus possessing immense potential as a valuable bioresource with high commercial value. However, utilizing seaweed as a bioresource comes with various challenges at processing levels, particularly at cost-effective downstream processing. Hence, this review highlights the advancement in seaweed biomass processing together with its application in food, nutraceuticals, pharmaceuticals, cosmetics, and non-food sectors. Additionally, the advancements in seaweed cultivation and the applications of seaweed in agriculture as a biostimulant, biofuel production, and packaging material are also reviewed. Finally, this review addresses the need for technology intensification, public awareness, and financial investment to enhance the commercialization and integration of seaweed-based products into the bioeconomy. The potential of seaweed to contribute to climate change mitigation and the circular economy is underscored, calling for further research and development to optimize its multifaceted applications. Full article

Porphyra specimens are red macroalgae with significant economic importance for food and pharmaceutical industries due to their physiological activities resulting from their bioactive compounds (BACs). Due to its economic importance, this research aimed to characterize the photosynthetic and biochemical aspects of the conchocelis and blade phases of Porphyra linearis to understand and help improve production of this algae. The algae were cultured for 7 days with nutrients for blade phase measurements, while another portion was cultured without nutrients for 21 days to release carpospores, which were cultivated for 4 months. For both phases, the content of BACs (chlorophyll a, carotenoids, phycobiliproteins, phenols, carbohydrates, proteins, mycosporine-like amino acids), antioxidant activity, and photosynthetic parameters were analyzed. Most of the parameters showed the blade phase had better results than conchocelis, except for carbohydrates. Phycobiliproteins showed no statistical differences between the phases. These findings highlight that conchocelis is not a good BACs source compared to the blade phase, but it is a crucial phase in the life cycle of Porphyra. Understanding the key parameters for maintaining the cultivation of conchocelis stocks for the development of the blade phase is a way to produce macroscopic biomass of this economically important algae throughout the year. Full article

This study aim to compare the extraction yield, antioxidant potential, and chemical composition of Chaetoceros costatus extracted with acetone, ethanol, and hexane. The freeze-dried diatom biomass was extracted by ultrasonication for 1 h at 40 °C. The antioxidant capacity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and oxygen radical absorbance capacity (ORAC), while the chemical profiles of the extracts were analyzed using high-performance liquid chromatography with high-resolution mass spectrometry with electrospray ionization (UHPLC-ESI-HRMS). The ORAC assay showed a 27% higher activity of the acetone extract, while the DPPH assay showed almost 3-fold higher DPPH inhibition. Pigments, fatty acids, sterols, and their derivatives were identified in all extracts. The chemical composition of ethanolic and acetonic extracts did not differ significantly, and hexane yielded the fewest compounds. The results of this study will contribute to extraction challenges that limit biotechnological application and exploitation of diatoms. Full article

This study aimed at producing a sourdough bread supplemented with two marine algae powders of Ulva lactuca and Gelidium corneum at 2.5, 5, 7.5, and 10% (w/w, g/100 g DW) at the laboratory scale using mixed starters prepared with three lactic acid bacteria (LAB) combinations (LCS1, LCS2, and LCS3). The phytochemical composition, nutritional value, organoleptic properties, and acceptability of algae bread by consumers were then assessed. Good results were obtained for enriched bread with Gelidium at 2.5% (GB1) with a reducing sugar of 0.77 ± 0.1%, total sugar of 36.90 ± 3.15, and protein content of 8.3 ± 0.2%. While total phenolic content was 8.32 ± 1.20 mg GAE/g DW, total flavonoids was 225.00 ± 11.31 mgQE/g DW, and the antioxidant activity ranged from 71.05 ± 3.71 to 82.93 ± 3.61%. Regarding enriched bread with Ulva at 10% (UB12), reducing sugar was 0.48 ± 0.03%, total sugar was 45.45 ± 5.75%, and protein content was 3.7 ± 0.07%. The total phenolic content value was 6.45 ± 1.19 mg GAE/g DW, total flavonoids was 191.20 ± 12.52 mgQE/g DW, while the antioxidant activity values ranged from 52.06 ± 6.21 to 80.51 ± 1.72%. Microbiological analysis showed that all pathogenic bacteria were not detected in algae bread. The consumer acceptability test revealed that bread enriched at the level of 10% of algae powder was significant for the five selected criteria (general appearance, crumb color, odor, taste, and texture). Traditional bread supplemented with Gelidium powder at 2.5% and Ulva powder at 10%, prepared with combined sourdough (LCS1), showed good antioxidant and nutritional properties and consumer acceptance. Full article

Seaweeds are the only source for phycocolloids. Commercial applications of phycocolloids depend on their chemical/physical properties, including their gel forming ability. Thus, gel strength values are important for seaweed growers and scientists. Gel strength measurements include the use of texture analyzers or rheometers, which are not always available for seaweed growers and scientists. Here, we describe a home-made apparatus for assessing gel strength through the weight of a water column required for breaking a gel surface. The system worked well at gel concentrations between 0.5 and 1.5%, giving values of 82–535 g cm⁻² and 163–754 g cm⁻² for agar and agarose gels, respectively. The lowest variations were obtained for gel sample volumes between 25 and 30 mL. The system was manually operated but no significant variations were observed between measurements conducted by the five different users. The readings were independent of the water column fill rate. The variations in gel strength values were similar to reports using other gel strength measuring devices. We propose the use of our apparatus as a flexible, affordable tool for the assessment of gel quality, which is suitable for research groups or seaweed farmers without access to expensive equipment, and with a need to quickly assess their seaweed of interest at a relevant time scale for cultivation or harvest. Full article

Laminaria hyperborea, a key species in marine forest ecosystems, is experiencing pressure at its southern distribution limit in northern Portugal due to climate change and human-induced stressors. The ongoing degradation of marine forests highlights the need for effective restoration strategies to protect biodiversity and maintain the essential services provided by these habitats. Cultivation of juvenile kelps in laboratory settings is a common approach shared across multiple strategies aimed at supporting reforestation efforts; however, the specific cultivation process for L. hyperborea remains largely underexplored. In this study, we tested two seeding densities to optimize the production of L. hyperborea recruits for reforestation initiatives. We assessed the effects of seeding density on juvenile development by measuring both area coverage and length. Our findings revealed that higher seeding density initially promoted greater area coverage (e.g., 8.69 ± 0.38 cm² vs. 3.35 ± 0.27 cm²) but reduced the length of individual recruits over time (e.g., 0.26 ± 0.0026 cm vs. 0.39 ± 0.003 cm at T3). This suggests that increased competition for resources at high densities limits individual growth. In contrast, lower densities produced larger, more robust individuals (e.g., 0.50 ± 0.004 cm vs. 0.262 ± 0.003 cm at T4), which may enhance post-transplantation survival in challenging environmental conditions. This suggests that utilizing lower seeding densities may improve individual growth while decreasing overall resource use and maintenance needs, promoting a more sustainable cultivation process and minimizing impacts on donor populations. However, further research is essential to refine the cultivation protocols and fully understand the variables influencing juvenile kelp development. Improving all phases of the restoration process, from laboratory cultivation to field deployment, will be critical for reducing costs, streamlining logistics, and ensuring the scalability of future kelp restoration efforts. Full article

Ascophyllum nodosum is an ecologically and economically important species forming marine forests in temperate regions. In Europe, this brown seaweed reaches its southern distribution limit in the north of Portugal, where populations are under climatic pressure. Conservation and restoration actions are essential to preserve the important ecological roles of these populations, including biodiversity enhancement. In this study, we assessed the effect of temperature and light on the development of the early life stages of A. nodosum, from gamete germination and rhizoid development to germling growth, in order to support the establishment of nursery protocols for producing seedlings that can be used in reforestation actions. We found that for this population, temperature around 12 °C and low-light conditions (40 μmol m⁻² s⁻¹) favor gamete germination, rhizoid development, and initial germling growth during the first month, after which higher light supply (>80 μmol m⁻² s⁻¹) is needed to sustain further growth stages. The results obtained in this study are relevant for the establishment of nursery methods for A. nodosum and should be complemented by further studies to determine more precisely the light and nutrient requirements to optimize growth in the germlings’ later growth stages. Full article