Seaweed Species Research Articles

Exploring Bioactive Compounds in Brown Seaweeds Using Subcritical Water: A Comprehensive Analysis.

In this study, we characterized the bioactive properties of three important brown seaweed species, Sargassum thunbergii, Undaria pinnatifida, and Saccharina japonica, by subcritical water extraction (SWE), as these species are well known for their beneficial health effects. Their physiochemical properties, including potential antioxidant, antihypertensive, and α-glucosidase inhibitory activity, and the antibacterial activity of the hydroysates were also analyzed. The highest total phlorotannin, total sugar content, and reducing sugar content in the S. thunbergii hydrolysates were 38.82 ± 0.17 mg PGE/g, 116.66 ± 0.19 mg glucose/g dry sample, and 53.27 ± 1.57 mg glucose/g dry sample, respectively. The highest ABTS+ and DPPH antioxidant activities were obtained in the S. japonica hydrolysates (124.77 ± 2.47 and 46.35 ± 0.01 mg Trolox equivalent/g, respectively) and the highest FRAP activity was obtained in the S. thunbergii hydrolysates (34.47 ± 0.49 mg Trolox equivalent/g seaweed). In addition, the seaweed extracts showed antihypertensive (≤59.77 ± 0.14%) and α-glucosidase inhibitory activity (≤68.05 ± 1.15%), as well as activity against foodborne pathogens. The present findings provide evidence of the biological activity of brown seaweed extracts for potential application in the food, pharmaceutical, and cosmetic sectors.

Evaluation of 3 northwest European seaweed species on enteric methane production and lactational performance of Holstein-Friesian dairy cows

Seaweeds have been studied for their ability to reduce enteric methane emissions of ruminants when fed as a feed supplement. In vivo research with dairy cattle is mainly limited to the seaweed species Ascophyllum nodosum and Asparagopsis taxiformis, whereas in vitro gas production research covers a broader range of brown, red, and green seaweed species from different regions. The objective of the present study was to determine the effect of Chondrus crispus (Rhodophyta), Saccharina latissima (Phaeophyta), and Fucus serratus (Phaeophyta), 3 common northwest European seaweeds, on enteric methane production and lactational performance of dairy cattle. Sixty-four Holstein-Friesian dairy cattle (16 primiparous, 48 multiparous) averaging (mean ± standard deviation) 91 ± 22.6 d in milk and 35.4 ± 8.13 kg/d fat- and protein-corrected milk yield (FPCM) were randomly assigned to 1 of 4 treatments in a randomized complete block design. Cows were fed a partial mixed ration [54.2% grass silage, 20.8% corn silage, and 25.0% concentrate; dry matter (DM) basis] with additional concentrate bait in the milking parlor and the GreenFeed system (C-Lock Inc.). The 4 treatments consisted of a control diet without seaweed supplement (CON), or CON supplemented with 150 g/d (fresh weight of dried seaweed) of either C. crispus (CC), S. latissima (SL), or a 50/50 mix (DM basis) of F. serratus and S. latissima. Milk yield (28.7 vs. 27.5 kg/d, respectively), fat- and protein-corrected milk (FPCM) yield (31.4 vs. 30.2 kg/d, respectively), milk lactose content (4.57 vs. 4.52%, respectively), and lactose yield (1,308 vs. 1,246 g/d, respectively) increased for SL compared with CON. Milk protein content was lower for SL compared with the other treatments. Milk fat and protein contents; yields of fat, protein, lactose, and FPCM; feed efficiency; milk nitrogen efficiency; and somatic cell count did not differ between CON and the other treatments. Depending on week of experiment, milk urea content was higher for SL compared with CON and CC. No effects were observed of the treatments compared with CON for DM intake, number of visits to the GreenFeed, or gas emission (production, yield, or intensity) of CO2, CH4, and H2. In conclusion, the seaweeds evaluated did not decrease enteric CH4 emissions and did not negatively affect feed intake and lactational performance of dairy cattle. Milk yield, FPCM yield, milk lactose content, and lactose yield increased, and milk protein content decreased, with S. latissima.

Comparative Study on the Effect of Phenolics and Their Antioxidant Potential of Freeze-Dried Australian Beach-Cast Seaweed Species upon Different Extraction Methodologies.

Brown seaweed is rich in phenolic compounds and has established health benefits. However, the phenolics present in Australian beach-cast seaweed are still unclear. This study investigated the effect of ultrasonication and conventional methodologies using four different solvents on free and bound phenolics of freeze-dried brown seaweed species obtained from the southeast Australian shoreline. The phenolic content and their antioxidant potential were determined using in vitro assays followed by identification and characterization by LC-ESI-QTOF-MS/MS and quantified by HPLC-PDA. The Cystophora sp. displayed high total phenolic content (TPC) and phlorotannin content (FDA) when extracted using 70% ethanol (ultrasonication method). Cystophora sp., also exhibited strong antioxidant potential in various assays, such as DPPH, ABTS, and FRAP in 70% acetone through ultrasonication. TAC is highly correlated to FRAP, ABTS, and RPA (p < 0.05) in both extraction methodologies. LC-ESI-QTOF-MS/MS analysis identified 94 and 104 compounds in ultrasound and conventional methodologies, respectively. HPLC-PDA quantification showed phenolic acids to be higher for samples extracted using the ultrasonication methodology. Our findings could facilitate the development of nutraceuticals, pharmaceuticals, and functional foods from beach-cast seaweed.

Screening and isolation of milk-clotting enzymes from seaweed

Cheese-making involves milk coagulation as a crucial step where calf rennet has been used traditionally as the milk-clotting enzyme in the cheese industry. This study investigated milk-clotting enzymes from seven species of seaweed and evaluated the parameters for their isolation and partial purification including post-harvest processing, extraction and purification methods. The saturation degree of ammonium sulphate and the precipitation stages were evaluated to obtain optimal purification conditions, and three desalting methods, namely dialysis, desalting column and the combination of dialysis and desalting column, were investigated to determine the most suitable method for ammonium sulphate removal. Protein extracts of all seven species of seaweeds exhibited some caseinolytic activity, but the extract of unprocessed (whole) dried samples had higher protein yields and stronger caseinolytic activities. The extract from one species, Gracilaria edulis, demonstrated the ability to clot milk. The evaluation of the purification method for G. edulis extract revealed an optimum single step of 50% saturation and ammonium sulphate precipitation with dialysis as the desalting method.

Phytochemical Screening and Antioxidant Activities of Some Seaweed from Kabung Island Waters West Kalimantan

Seaweed is one of the prima donna marine biota which is widely used as a natural antioxidant. Various species of seaweed are found growing naturally in the waters of Kabung Island, West Kalimantan. This study aims to determine the phytochemical content and antioxidant activity of each genus Turbinaria, Hypnea and Caulerpa from those collected in the waters of Kabung Island. Seaweed extraction uses maceration method with methanol to remove active compounds. Next, a phytochemical screening was performed using specific reagents such as alkaloids, steroids, flavonoids, tannins and saponins which will change color or form precipitates. The free radical scavenging method of 2,2-diphenyl-1-picrylhydrazyl (DPPH) solution was used to test the antioxidant activity of each seaweed extract. The active compound in the sample extract will be formed if there is a change in the color of free radicals from dark purple to light yellow or clean. The results showed that the phytochemical screening of the three seaweed extracts contained tannins, flavonoids and saponins. Meanwhile, positive alkaloids were found in Turbinaria and Caulerpa extracts, and steroids were indicated by the genus Hypnea and Caulerpa. Antioxidant screening showed that Caulerpa extract was categorized as a potent antioxidant with an IC50 value of 88.57 ppm, higher than the IC50 of Turbinaria and Hypnea extracts, which were 114.32 and 138.42 ppm respectively and classified as weak antioxidants.

Range expansion of some non-indigenous seaweeds along the coasts of Brittany – English Channel

Abstract Non-indigenous seaweed species have been introduced to the coasts of Brittany, France for decades, with an increasing arrival rate since the 1970s due to both the introduction of the Pacific oyster and increased maritime traffic. In this study, seven species of red macroalgae originating from the Pacific Ocean were found in new locations around the coasts of Brittany between 2018 and 2022. The seaweed species belong to four different orders: Ceramiales (Antithamnion hubbsii, Polysiphonia morrowii, and Symphyocladiella dendroidea), Halymeniales (including Pachymeniopsis lanceolata and Polyopes lancifolius), Rhodymeniales (Botryocladia wrightii), and Gigartinales (Solieria sp.). The dispersal mode and putative invasive potential of each species were examined, and the species were described in terms of their macroscopic and microscopic appearance and habitat. These finds result from a combination of citizen science and long-term monitoring. Used together, these two approaches can aid in the detection of these species on other European coasts and in understanding their dispersion.

Comparative study on the effect of different drying techniques on phenolic compounds in Australian beach-cast brown seaweeds

Marine seaweeds have increased their interest among researchers worldwide due to their beneficial health-promoting compounds such as phenolic compounds. Drying is one of the ancient methodologies to preserve food for a long shelf-life. It will help remove the moisture content from the seaweed and thus increase the bioactive compounds' shelf-life. This study was conducted to compare the fresh and dried seaweed's phenolic compounds of five different brown seaweeds, the seaweed were dried by using three different drying methods (freeze, oven, vacuum), and to evaluate their potential antioxidant activities. Subsequently, individual compounds were characterized and identified using LC-ESI-QTOF-MS/MS. Vacuum-dried Cytosphora sp., had high TPC (39.53 GAE mg/g), TFC (3.40 QE mg/g), DMBA (2.86 PGE mg/g), PBA (27.90 PGE mg/g), and FDA (0.85 PGE mg/g) whereas freeze-dried Cytosphora sp., had high radical scavenging activity in DPPH (47.66 TE mg/g). However, vacuum-dried Cytosphora sp., exhibited high antioxidant potential in FRAP (91.28 TE mg/g), ABTS (80.86 AAE mg/g), RPA (96.90 AAE mg/g), and ·OH-RSA (252.22 TE mg/g). Freeze-dried Ecklonia radiata had high antioxidant potential in FICA (14.70 EDTA mg/g) and freeze-dried Sargassum sp., exhibited high total antioxidant activity (29.29 AAE mg/g). The total phenolic and total flavonoid content were highly correlated with antioxidant potential. Construction of the Venn diagram demonstrated high phenolic profiling of unique compounds in Cystophora sp., and in the vacuum-dried seaweeds followed by the freeze-dried seaweeds. The LC-ESI-QTOF-MS/MS identified and characterized 22 compounds in vacuum-dried and 20 compounds in oven-dried seaweed species. While 18 and 5 compounds were identified in freeze-dried and fresh seaweed samples, respectively. Our results will provide vital information to industries including food, pharmaceutical, and nutraceutical for upscale drying and extraction of phenolic compounds.

In Vitro and In Vivo Antidiabetic Effects of Acidic Polysaccharides Extracted from Seaweeds.

We evaluated the α-glucosidase inhibitory activity of acidic polysaccharides (APs) extracted from seaweeds in vitro and their antidiabetic effects in KK-Ay mice. The α-glucosidase inhibitory activity of APs was differed among various seaweed species. Some APs showed higher inhibitory activity in the high-molecular-weight range, whereas others showed higher inhibitory activity in the low-molecular-weight range. Mice were fed low-molecular-weight APs from hijiki (LMWAPsH), which showed higher α-glucosidase inhibitory activity. Fasting blood glucose and HbA1c levels were significantly lower in the LMWAPsH group than in the control group (p<0.01). The calculated homeostasis model assessment-insulin resistance in the LMWAPsH group was significantly lower than that in the control group (p<0.05). These results suggest that α-glucosidase inhibitory activity differ among APs from different seaweed species, and each have an optimum molecular-weight range, and that LMWAPsH prevents the hyperglycemia in KK-Ay mice.

Biochemical and Nutritional Characterization of Edible Seaweeds from the Peruvian Coast.

In Peru, the number of species of edible seaweeds within the genera Chondracanthus, Porphyra (hereafter P.), Pyropia (hereafter Py.), and Ulva has not been fully established, nor is there a significant level of information available related to their chemical and nutritional composition. This study involved the biochemical analysis of species belonging to ten genera of macroalgae, known edible and some of which have the potential to be used as food, including six red (Callophyllis, Chondracanthus, Mazzaella, Porphyra, Pyropia, and Rhodymenia), two green (Ulva and Codium), and two brown (Eisenia and Lessonia) species collected along the Peruvian coast (6°-17° S). In the evaluation of 37 specimens, differences were found in the proximal composition, amino acid composition, and fatty acid profiles, which were specific to subgroups and supported their taxonomic classification, mainly at the order level. The red algae Porphyra/Pyropia (Bangiales) had the highest average percentage of protein (24.10%) and carbohydrates (59.85%) and the lowest percentage of ash (7.95%). Conversely, the brown alga Eisenia (Laminariales) had the lowest average percentage of protein, with different values related to the structure: 14.11% at the level of the frond and 9.46% at the level of the stipe. On the other hand, Bryopsidales green algae showed the highest average percentages of lipids (5.38%). The moisture percentages ranged from 4 to 16%, and no relevant significant differences were shown between the orders. The characteristic amino acids in all of the studied groups were glutamic acid, aspartic acid, alanine, and leucine. The highest average of the essential amino acids ratio was obtained for the Gigartinales red algae (48.65%), and the highest values of the essential amino acid index (EAAI) were obtained for the Ulvales, Laminariales, Gigartinales, and Rhodymeniales algae (EAAI > 0.92). The highest average relative percentage of fatty acids was obtained for polyunsaturated fatty acids, followed by saturated fatty acids. The major component of the ω6 fatty acids from red and brown algae was arachidonic acid (C20:4n - 6). The highest level of ω3 fatty acids was observed for the eicosapentaenoic acids (EPA) in red algae. The highest median ω6/ω3 ratio was displayed by the red alga Callophyllis variegata (Gigartinales). A detailed knowledge of edible seaweeds, and those considered potentially edible, would help to diversify the diet based on macroalgae in Peru.

Photosynthetic pigments and photoprotective metabolites of Colombian pacific marine macroalgae in response to contrasting ultraviolet-index periods

Tropical macroalgae have developed specific defense mechanisms, synthesizing photoprotective molecules to cope with solar radiations, especially ultraviolet radiation, which hits them intensely. Despite the vast Colombian marine biodiversity, not all the country's coastlines have received the same attention, like the Pacific coast. In this study, we assessed photosynthetic pigments (chlorophylls and carotenoids) and photoprotective compounds (mycosporine-like amino acids - MAAs) in seaweeds from the Colombian Pacific coast. We collected seven species of seaweeds, namely Boodleopsis verticillata, Bostrychia calliptera, B. radicans, B. cf. scorpioides; Catenella impudica, Cladophora graminea and Rhizoclonium riparium, easily found in supralittoral and mangrove ecosystems, at low tide, in contrasting periods of high and low UV index over the year of 2021. The sampling area encompassed a latitudinal gradient (3° S to 6° S) along the Colombian Pacific coast, changing the pattern of the chlorophyll-a and total carotenoid content in different species collected in contrasting UV-index periods. MAAs were quantified using standards (shinorine, porphyra-334, and palythine). This study corroborates the hypothesis that tropical species produce higher concentrations of MAAs in response to UV radiation, with significant differences in the high UV-index period. The highest MAA content (5.68 mg.g−1 DW) was reported in Bostrychia calliptera during the high UV-index period. Ceramiales and Cladophorales species represented a photoprotective potential with at least six different MAAs. Shinorine, palythine and porphyra-334 were quantified; and mycosporine-methylamine-serine and aplysiapalythine C were putatively identified by LC-MS/MS dereplication, this, therefore representing a pioneer study on the chemical composition of Colombian Pacific marine macroalgae.

New Analytical Strategy for Bioaccessibility Evaluation of Bromine and Iodine from Edible Seaweeds.

A strategy for determining the bioaccessibility of bromine and iodine from edible seaweeds was proposed for the first time using microwave-induced combustion (MIC) and ion chromatography coupled to mass spectrometry (IC-MS) after in vitro digestion. The concentrations of bromine and iodine in edible seaweeds using the proposed methods (MIC and IC-MS) were not statistically different from those using MIC and inductively coupled plasma mass spectrometry (p > 0.05). Trueness was assessed by recovery experiments (101-110%, relative standard deviation <10%). Following an in vitro digestion protocol, MIC was proposed as sample preparation for bioaccessible and residual fractions. Using this strategy, the mass balance totaled from 97 to 111%. No statistical difference (p > 0.05) was observed between the total concentration of bromine or iodine and their concentration in bioaccessible and residual fractions for three edible seaweed species, indicating full analyte quantification in the fractions.

Isolation and Identification of Seaweed-Associated Bacteria and Their Antibacterial Activity against Skin Disease Agents

Bacteria associated with marine organisms have become the focus of worldwide research for their potential to generate bioactive substances, such as antibacterial compounds. This study aimed to identify the antibacterial activity of seaweed-associated bacteria in Teluk Awur Jepara, Indonesia, against Propionibacterium acnes and Staphylococcus epidermidis. Three seaweed species, Caulerpa racemosa, Padina minor, and Halimeda opuntia, were sampled in this study. Their isolates were selected tested for antibacterial activity against pathogenic bacteria using the paper disc diffusion and Minimum Inhibitory Concentration methods and were molecularly identified based on the 16s RNA gene (27F-1492R). Twenty-one isolates were isolated from the 3 seaweed species: 11 from C. racemosa, 6 from P. minor, and 4 from H. opuntia. Further testing revealed potential isolates (C2a, C2c, C2d, and H2d) with antibacterial activity against P. acnes F2 ATCC 6919 and S. epidermidis FNCC-0048. Gene-based identification using 16s RNA (27F-1492R) demonstrated the occurrence of 4 bacterial species, namely Vibrionaceae bacterium PH25 (99.86 %), Vibrio alginolyticus strain GS MYPK1 (99.65 %), Salinivibrio costicola strain M318 (99.86 %), and V. alginolyticus strain 2014V-1011 (99.93 %). HIGHLIGHTS Bacteria associated with racemosa, P. minor, and H. opuntia can show strong antibacterial properties capable of mitigating the growth of P. acnes F2 ATCC 6919 and S. epidermidis FNCC-0048 Seaweed-associated bacteria and their antibacterial activity against skin disease agents. Gene-based identification using 16s RNA (27F-1492R) demonstrated the occurrence of 4 bacterial species, namely Vibrionaceae bacterium PH25 (99.86 %), Vibrio alginolyticus strain GS MYPK1 (99.65 %), Salinivibrio costicola strain M318 (99.86 %), and alginolyticus strain 2014V-1011 (99.93 %) The major bacteria species on the scalps of those suffering from dandruff, we believe these isolates may be useful for dandruff therapy GRAPHICAL ABSTRACT

A new evaluation system of iron bioavailability in seaweed

In marine ecosystems, the avid binding of iron (Fe) to organic ligands influences Fe bioavailability in seaweed. This study aimed to elucidate Fe's biological availability to seaweed and develop a simple and rapid bioassay method as a new evaluation system. Undaria pinnatifida was used as a model seaweed species and the actual seaweed samples were collected using the 0.5 m × 0.5 m quadrat from the Mashike Bay area of Hokkaido, Japan. Chlorophyll fluorescence measurements were utilized as an index to evaluate the biological -effectiveness of Fe and compared with the results of culture tests based on growth. The effect of Fe content on media, pre-culture, concentrations and types of chelating and reducing agents in clearing solutions, cleaning time, Fe removal effect, and resistance to seaweed were systematically optimized to obtain the maximum efficacy of the washing solution. A bioassay was developed to evaluate the Fe environment by combining chlorophyll fluorescence measurements. The findings suggest that the tolerance of seaweeds to the wash solution is strongly influenced by the concentrations of the chelating and reducing agents than their types. Washing with 0.02 M Ti-Citrate/EDTA solution for 80 s was the most effective in terms of maximum Fe removal with minimum cell damage. The application of pre-culture and chemical pre-treatment methods under Fe deficiency to the culture strain confirmed the maximum reproducibility in the culture test. Finally, the developed method was applied to actual seaweed samples and was found to be applicable to many seaweed species. However, the method was less robust for some seaweed species and depended on the seaweed growth stage.

In Vitro Evaluation of the Wound Healing Properties and Safety Assessment of Fucoidan Extracted from Sargassum angustifolium

Seaweeds are rich in fucoidan, which has various biologic effects. So far, a lot of research has been conducted on the biological effects of fucoidan extracted from various species of seaweed. However, the effects of partially purified extract of Sargassum angustifolium (PPE-SA) on wound healing (cell migration) of adipose-derived mesenchymal stem cells (ADMSCs) have not yet been studied. In this experimental study, crude fucoidan was extracted from S. angustifolium using an advanced method. After removing lipids, pigments and low molecular weight compounds with ethanol and removal of alginate with CaCl2, polysaccharides in the remaining material were extracted with hot water (60ºC). The polysaccharides of the resulting extract were precipitated with ethanol. Then, the wound healing and safety of PPE-SA on ADMSCs were investigated by MTT and the scratch assay, respectively. The MTT assay showed that PPE-SA did not only have a negative effect on the growth of mesenchymal cells but at some concentrations improved their growth by up to 1.5 times. The PPE-SA also increased ADMSCs migration by 76% and 142% after 48 h and 72 h incubation, which showed the superiority of this seaweeds extract over many other reported species and genera. The results of this study showed that an extract of this seaweed obtained by this method has the potential to promote the growth of mesenchymal stem cells and may have a high potential for use in tissue engineering applications.

Assessment of Bioaccumulation of Heavy Metals and Their Ecological Risk in Sea Lettuce (Ulva spp.) along the Coast Alexandria, Egypt: Implications for Sustainable Management

The pollution of aquatic ecosystems is an issue facing many countries all over the world and may result in issues such as eutrophication in coastal zones. Managing this eutrophication is a real challenge. The current study focuses on the investigation and identification of aquatic environmental characteristics, including the sediments, waters, and seaweed, of seven eutrophicated locations along the Mediterranean coast of Alexandria (Egypt). Different ecological risk assessment and bioaccumulation factors were calculated in order to identify the probable pollution source and the degree of the problem, in addition to the accumulation of heavy metals in the seaweed. The characteristics of the seaweed, sediments, and waters were chemically analyzed and heavy metals were measured. The genetically and biochemically identified seaweed species were Ulva compressa, Ulva fasciata, Ulva lactuca and Ulva linzea. The sediments of the El-Tabia location contained the highest concentrations of Cd, Co, Ni, and Pb, because this location receives these elements from the El-Amia drain. The Abu Qir location was found to contain the highest concentrations of the same heavy metals in the studied water samples because it was located much closer to the Abu Qir harbor. Ecological risk assessment indices indicated moderate to high contamination for most of the studied elements and locations. The results of the bioaccumulation factor analysis indicated that the studied seaweed species are accumulators of trace elements. These seaweed species should be further investigated concerning ecotoxicology if they are to be used in the human diet and for other benefits. This study opens many windows of research to be investigated in the future regarding the sustainable management of polluted coastal zones.

Distribution and Biochemical Composition of Seaweeds in relation to Hydro-chemical Characters of Marine Water

The aim of this study was to determine the distribution pattern, pigments and biochemical composition of various seaweed species collected from the Gopnath coast in Gujarat, India from August 2021 to December 2021 as well as to examine physico-chemical variables in marine waters. Besides, the relationship between the pigment, biochemical content of seaweed species and hydrochemical characters was also investigated with principal component analysis (PCA). There are total of nine species with the highest number of Chlorophyta species. During the investigation period, the distribution and occurrence of the species changed greatly. Results indicate that the chlorophyta had the highest chlorophyll content, on the other hand carotenoids were found greater in Rhodophyta members. According to a statistical analysis (Correlation) computed among environmental parameters and pigment, it was observed that the chlorophyll content was positively correlated with pH, salinity and hardness whereas carotenoid shows positive correlation with temperature and dissolved oxygen of selected site. Moreover, the principal component analysis shows that the pH, electrical conductivity (EC), salinity, hardness and alkalinity are the main factor for marine water quality whereas principal component analysis of metabolites of seaweed shows that the carbohydrate and amino acids are the main principal components of Chlorophyta species. Protein is the main principal component of Rhodophyta specie. Based on the results obtained, we can conclude that the hydro-chemical characters may play a role in the biosynthetic pathways of seaweed.

Investigating the Mechanisms Underlying the Low Irradiance-Tolerance of the Economically Important Seaweed Species Pyropia haitanensis.

Pyropia haitanensis, one of the most economically and ecologically important seaweed species, is often exposed to persistent or transient low irradiance (LI), resulting in limited yield and quality. However, the mechanisms mediating P. haitanensis responses to LI are largely unknown. In this study, LI-tolerant (LIT) and LI-sensitive (LIS) P. haitanensis strains were compared regarding their physiological and transcriptomic changes induced by 1 and 4 days of LI (5 μmol photons/m2·s). The results indicated that the inhibition of photomorphogenesis and decreases in photosynthesis and photosynthetic carbon fixation as the duration of LI increased are the key reasons for retarded blade growth under LI conditions. A potential self-amplifying loop involving calcium signaling, phosphatidylinositol signaling, reactive oxygen species signaling, and MAPK signaling may be triggered in blades in response to LI stress. These signaling pathways might activate various downstream responses, including improving light energy use, maintaining cell membrane stability, mitigating oxidative damage, to resist LI stress. Additionally, the LIT strain maintained transcriptional homeostasis better than the LIS strain under LI stress. Specifically, photosynthesis and energy production were relatively stable in the LIT strain, which may help to explain why the LIT strain was more tolerant to LI stress than the LIS strain. The findings of this study provide the basis for future investigations on the precise mechanisms underlying the LI stress tolerance of P. haitanensis.

Range‐edge populations of seaweeds show niche unfilling and poor adaptation to increased temperatures

AbstractAimGlobal warming is affecting the distribution of species worldwide, but the level of adaptation of edge populations to warmer temperatures remains an open question. Here, we assess the thermal tolerance of populations of two habitat‐forming seaweeds along their latitudinal range, using thermal niche unfilling to assess their resilience to global warming.LocationEuropean Atlantic coastline.TaxonAscophyllum nodosum (Linnaeus) Le Jolis (Phaeophyceae) and Chondrus crispus Stackhouse (Rhodophyta).MethodsWe studied the ecotypic variation in upper survival temperatures (USTs) by measuring survival and growth of adults representing populations under a gradient of seawater temperature (12–30°C). Comparing the USTs with maximum seawater temperatures obtained from satellites, we investigated safety margins and niche unfilling states, both in recent history and under future climate scenarios.ResultsUSTs (≈24°C) did not differ significantly between populations, except for higher values (27.9°C) for the northernmost populations (cold edge) of A. nodosum. Populations of both species had thermal safety margins over the last few decades (from 1982 to 2021). However, projections based on USTs showed that in several years these margins have been eliminated and will completely disappear in the Bay of Biscay under RCP4.5 and RCP6.0 2090–2100 IPCC scenarios for C. crispus and under RCP8.5 for both species, threatening the populations there.Main ConclusionsSouthern marginal populations were not better adapted to global warming than populations elsewhere. Both seaweed species tolerated higher temperatures than the ambient maxima, suggesting a thermal niche unfilling state with thermal safety margins in their recent history. However, those are being depleted by ongoing climate change and this trend is predicted to increase. Marine heat waves are important threats to these habitat‐forming species, transiently reducing or even eliminating safety margins in the hottest parts of the European Atlantic coastline, contributing to explaining the distributional gap there.

Prevalence of Ice-Ice Disease in Kappaphycus spp. and Eucheuma denticulatum Farms in Sibutu, Tawi-Tawi, Philippines

Kappaphycus spp. and Eucheuma denticulatum are commercially farmed in the world, notably in tropical countries such as Indonesia, Philippines, and Malaysia. Diseases and pests, particularly ice-ice disease, are the major hurdles in the sustainability of eucheumatoid seaweed culture. In this study, ice-ice disease prevalence in Kappaphycus and Eucheuma farms in Sibutu, Tawi-Tawi, Philippines, was assessed and compared according to species, farm depth, and time. Results revealed that in deep water farms, ice-ice disease prevalence was significantly lower in K. striatus (4.29±0.97%) than in K. alvarezii (10.53±2.64%) in July. In shallow water farms, E. denticulatum had the highest ice-ice prevalence (21.97±1.73%) significantly among the assessed seaweed species during August, and K. alvarezii had the lowest ice-ice disease occurrence (5.43±1.98%) significantly during September. In terms of depth water farm and time comparison, ice-ice disease prevalence (7.41±1.50% - 27.04±4.66%) in deep water (exceeding 2.47±0.16 m during low tide) did not differ significantly from that prevalence (11.35±1.69% - 12.91±1.93%) in shallow water farms (0.61±0.29 m during low tide) across time. This study suggests that ice-ice disease is still a prevalent and persistent problem in eucheumatoid seaweed farming.

Potential for Use of Seaweed as a Fish Feed Ingredient: A Review

Seaweeds, also known as macroalgae are marine plants used widely as food and applied in other food allied industries, pharmaceuticals, cosmetics and agrochemical industries. Their production has increased over the years with advancement in identification and cultivation of different seaweed species. Over the years seaweeds have been explored as a food due to their nutrition value and bioactive compounds that are beneficial to human nutrition and health. With this principle, seaweeds can also be used as feed ingredient in aqua feeds especially due to the fact that it is a source of omega-3 and hence can be used as an alternative to fish oil whose supply has declined. Studies have shown that polyunsaturated fatty acids which are important in fish nutrition can account for about 50% of total fatty acids in seaweeds. In addition to being a good source of polyunsaturated fatty acids, seaweeds provide protein and minerals, vitamins. They are also characterized with high levels of protein rich in all the amino acids relative to some higher plant-based protein crops like soya bean.&#x0D; &#x0D; This review, therefore, aims to look at the potential of seaweed as an aqua feed ingredient with the emphasis on the nutritional characteristics.