Algal Treatments Research Articles

Survival, immune response and growth of Penaeid shrimp as affected by immunostimulants: A meta-analysis

Immunostimulants represent the most innovative approach for combating shrimp diseases. They are molecules that effectively enhance the host's nonspecific defenses against invading microorganisms. However, methodological differences exist among immunostimulants based on the same source. Therefore, conducting a meta-analysis is essential to derive valid conclusions. The effect size value utilized in this study was Hedges' d. Heterogeneity among studies was assessed using the DerSimonian and Laird tests (Q-statistic). Meta-regression analysis was conducted to explore the sources of heterogeneity in treatment effects. In this study, dose served as a covariate because it was the only continuous variable that significantly contributed to the observed heterogeneity. Funnel plots and the fail-safe number were employed to assess publication bias within the datasets. The article collection process followed the PRISMA methodology. Based on the results of the meta-analysis and meta-regression conducted with 83 articles, it can be concluded that immunostimulants have a significant effect, characterized by high category standard mean difference (SMD) values, on the survival, growth, and immune response of Penaeid family shrimp. Among potential immunostimulants options, algae ingredients exhibited the most favorable effects on the survival, growth, and immune response of Penaeid family shrimp. Subgroup analysis outcomes revealed that various extraction methods significantly impacted the efficacy of immunostimulants, with the ethanol solvent method proving to be the most effective. Among different administration methods, no significant effect was observed on immunostimulant efficacy across all parameters, with positive SMD values for all administration methods. Regarding challenged test pathogens, immunostimulants were observed to enhance immune response, survival, and weight gain against various pathogens. Meta-regression results indicated that algal treatments had a lower optimal dose point, leading to decreased efficacy as the dose increased. In contrast, fungi exhibited a higher optimum dose point, resulting in increased efficacy at higher doses.

Anti-nemic potential of Laurencia papillosa and Dilophys fasciola biosynthesized nano-extracts against tomato root-knot nematode Meloidogyne incognita

Due to the damaging effects of root-knot nematodes on crops and the dangerous effects of chemical nematicides on both people and the environment in Egypt, the purpose of this study was to assess the power of polysaccharides and polyphenol extracts as well as their nano-forms from marine algae (Laurencia papillosa and Dilophys fasciola) used as eco-friendly alternatives for the control of Meloidogyne incognita. The nano-forms of algal extracts efficiently suppressed M. incognita egg hatching and increased juvenile mortality compared to the control. The tested treatments effectively decreased galls and egg masses of tomato roots compared to the control in the field. Dilophys fasciola extract and its nano-form showed promising nematicidal activity compared to L. papillosa extract. Generally, algal treatments boosted tomato plant defense system against M. incognita by triggering the production of some biochemical constituents such as phenolic compounds, polyphenol oxidase and chitinase enzymes. Consequently, the productivity and quality parameters of tomato fruits significantly increased.

Most treatments to control freshwater algal blooms are not effective: Meta-analysis of field experiments.

Harmful algal blooms negatively impact freshwater, estuarine, and marine systems worldwide, including those used for drinking water, recreation, and aquaculture, through the production of toxic and nontoxic secondary metabolites as well as hypoxic events that occur when algal blooms degrade. Consequently, water resource managers often utilize chemical, bacterial, physical, and/or plant-based treatments to control algal blooms and improve water quality. However, awareness of available treatments may be limited, and there is ambiguity among the effects of algal bloom treatments across studies. Such variation within the literature and lack of knowledge of other tested treatments leave uncertainty for water resource managers when deciding what treatments are best to control algal blooms and improve water quality. Our primary objective was to synthesize data from 39 published and unpublished studies that used one of 28 chemical, bacterial, physical, and/or plant-based treatments in field experiments on various water quality measurements, including phytoplankton pigments and cell density, cyanobacterial toxins (microcystin), and common off-flavors (i.e., taste and odor compounds; geosmin and 2-methylisoborneol). We hypothesized that treatments would improve water quality. Across all studies and treatment types (227 effect sizes), water quality improvements were observed when measured at the time of greatest decline following treatment or at the end of the experiment. However, these findings were primarily mediated by only four chemicals, namely copper sulfate, hydrogen peroxide, peracetic acid, and simazine. None of the bacterial, physical, or plant-based treatments were shown to significantly improve water quality by themselves. Results from this synthesis quantitatively showed that most treatments fail to improve water quality in the field and highlight the need for more research on existing and alternative treatments.

Enhancing the Growth Performance, Cellular Structure, and Rubisco Gene Expression of Cadmium Treated Brassica chinensis Using Sargassum polycystum and Spirulina platensis Extracts

Cadmium (Cd) is one of the highly toxic, non-essential heavy metals that inhibit plant growth and development by prompting chlorophyll loss and affecting photosynthetic activities. This study investigated the efficacy of Spirulina platensis and Sargassum polycystum extracts in alleviating Cd stress in Pak Choi at morpho-biochemical, anatomical, and molecular levels. Different concentrations (0, 25, 50, and 100 mL/L) of S. polycyctum (SAR), S. platensis (SPI), and a mixture of both extracts (SS) were exposed to 100 mg/kg Cd-contaminated Pak Choi seedlings. Non-Cd-treated Pak Choi and Cd-contaminated Pak Choi without algal extracts were assigned as positive and negative controls, respectively. The results showed that the application of algal extracts increased the plant height, fresh weight (FW), and dry weight (DW) as the extract level increased. This was greatest in 100SS with 37.51% (shoot length), 68.91% (root length), 110.8% (shoot DW), and 216.13% (root DW), while an increase of 176.7% (shoot FW) and 256.9% (root FW) was seen in the 100SPI treatment. Chlorophyll a, b, carotenoid, and chlorophyll fluorescence increased significantly after the treatment with 100SS. Antioxidant enzymes CAT, APX, POD, and protein were significantly increased in 100 mL/L extracts by 28.13% (100SS), 36.40% (100SAR), 46.92% (100SS), and 153.48% (100SS), respectively. The same treatment was also identified to dominate the development of root structures such as total length, surface area, projected area, diameter, volume, tips, and fork number. The highest reduction of Cd content in the root and shoot of Pak Choi was observed in 100SS with a 53.8% and 39.88% decrease, respectively. Increasing algal extract concentration also improved the leaf histological characteristics substantially, such as stomatal size and opening, mesophyll tissues, and vascular bundles. In addition, the fold change ratio of the Rubisco gene at 100SS treatment was noticeably greater than other algal extract treatments, with a 0.99 fold change when compared with the untreated sample. This present study illustrated that Sargassum polycyctum and Spirulina platensis extracts have the potential to effectively alleviate Cd stress in Pak Choi plants, especially with the application of 100 mL/L of an algal extract mixture. These findings contribute to the development of sustainable strategies for mitigating Cd toxicity in crops.

Alleviate the Drought Stress on Triticum aestivum L. Using the Algal Extracts of Sargassum latifolium and Corallina elongate Versus the Commercial Algal Products.

Herein, two seaweed extracts (Sargassum latifolium and Corallina elongate), and two commercial seaweed products (Canada power and Oligo-X) with a concentration of 5% were used to alleviate the drought stress on wheat plants. The extract of C. elongate had the highest capacity to ameliorate the deleterious effects of water scarcity followed by S. latifolium and the commercial products. The drought stress reduced wheat shoots length and the contents of pigments (chlorophyll and carotenoids), carbohydrates, and proteins. While the highest increment in the total carbohydrates and protein contents of the wheat shoot after two stages, 37-and 67-days-old, were noted in drought-stressed plants treated with C. elongate extract with values of (34.6% and 22.8%) and (51.9% and 39.5%), respectively, compared to unstressed plants. Decreasing the activity of antioxidant enzymes, peroxidase, superoxidase dismutase, and polyphenol oxidase in drought-stressed plants treated with algal extracts indicated amelioration of the response actions. Analysis of phytohormones in wheat plants exhibited increasing GA3 and IAA contents with percentages of (20.3-13.8%) and (72.7-25%), respectively. Interestingly, all morphological and metabolic characteristics of yield were improved due to the algal treatments compared with untreated drought-stressed plants. Overall, the algal extracts, especially those from seaweed of C. elongate, could represent a sustainable candidate to overcome the damage effects of water deficiency in the wheat plant.

Remarkable Natural Biological Resource of Algae for Medical Applications

With increasing consumer awareness of the use of natural products in pharmaceuticals and medicine, it is noted that algae can be considered an appropriate source. Algae produce many bioactive components, which have application potential in pharmaceutical industries, such as fatty acids, phycobiliprotein, polysaccharides, phenolic compounds, carotenoids, and so on. However, it is still a long way before the truly widespread application of algae in medicine, and some research and technical bottlenecks still need to be resolved for further practical use. Here, we provide an in-depth review of the current understanding of algal-based medical application, with a focus on the main pharmaceutical activity and current application stage includingin vitro, animal, and clinical studies. Furthermore, we propose some possible solutions to the obstacles that should be overcome for achieving the practical applications of algal-based medicine. Notably, animal and clinical studies on algal drugs and treatments should continue to push forward and expand for promoting the practical applications. Moreover, the developments in interdisciplinary research of algal biology and other disciplines provide new insight for driving algae-based medical application.

Fucoidan and Alginate from the Brown Algae Colpomenia sinuosa and Their Combination with Vitamin C Trigger Apoptosis in Colon Cancer.

Brown seaweeds are producers of bioactive molecules which are known to inhibit oncogenic growth. Here, we investigated the antioxidant, cytotoxic, and apoptotic effects of two polysaccharides from the brown algae Colpomenia sinuosa, namely fucoidan and alginate, in a panel of cancer cell lines and evaluated their effects when combined with vitamin C. Fucoidan and alginate were isolated from brown algae and characterized by HPLC, FTIR, and NMR spectroscopy. The results indicated that highly sulfated fucoidans had higher antioxidant and cytotoxic effects than alginate. Human colon cancer cells were the most sensitive to the algal treatments, with fucoidan having an IC50 value (618.9 µg/mL−1) lower than that of alginate (690 µg/mL−1). The production of reactive oxygen species was increased upon treatment of HCT-116 cells with fucoidan and alginate, which suggest that these compounds may trigger cell death via oxidative damage. The combination of fucoidan with vitamin C showed enhanced effects compared to treatment with fucoidan alone, as evidenced by the significant inhibitory effects on HCT-116 colon cancer cell viability. The combination of the algal polysaccharides with vitamin C caused enhanced degeneration in the nuclei of cells, as evidenced by DAPI staining and increased the subG1 population, suggesting the induction of cell death. Together, these results suggest that fucoidan and alginate from the brown algae C. sinuosa are promising anticancer compounds, particularly when used in combination with vitamin C.

Effects of Sargassum virgatum extracts on the testicular measurements, genomic DNA and antioxidant enzymes in irradiated rats

Background Oxidative stress and reactive oxygen species (ROS) are primarily responsible for the development of male infertility after exposure to γ-irradiation. The present work aimed to assess the ameliorative and therapeutic roles of the aqueous and ethanolic extracts of the edible seaweed Sargassum virgatum (S. virgatum) on spermatogenesis and infertility in γ-irradiated Wistar rats. Materials and methods Induction of infertility was performed by exposing the rats to 137Cs-gamma rays, using a single dose of 3.5 Gy. γ-irradiated rats were given the S. virgatum ethanolic (S. virgatum-EtOH) and aqueous extracts intraperitoneally on a daily base for two consecutive weeks at doses of 100 and 400 mg/kg body weight (b.wt.) for each seaweed extract. Morphometric data of the testes, semen quality indices, antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione peroxidase (GPx), and deoxyribonucleic acid (DNA) fragmentation were assessed. The results obtained were taken during two-time intervals of 15 and 60 days from the commencement of the algal treatments. In vitro antioxidant assays and polyphenolic compounds of S. virgatum were characterized. Results Significant negative changes in the semen quality and morphometric data of the testes, as well as remarkable DNA fragmentation, were detected in the irradiated rats compared to the control. The levels of the endogenous antioxidant enzymes (SOD, CAT, GSH, and GPx) were also significantly diminished. Nonetheless, treatments of γ-irradiated rats with the S. virgatum-EtOH and aqueous extracts significantly improved the above-mentioned enzymes, in addition to noteworthy amendments in the dimensions of the testes, the semen quality, as well as the DNA structure. Conclusions The ameliorative potency of S. virgatum to cure γ-irradiation-induced male infertility, particularly 400 mg/kg ethanolic extract for 60 days, is the result of the consistent therapeutic interventions of its potent antioxidant and anti-apoptotic polyphenols, particularly protocatechuic, p-hydroxybenzoic, rosmarinic, chlorogenic, cinnamic and gentisic acids, as well as the flavonoids catechin, hesperidin, rutin and quercetin. Besides its high-value nutraceutical importance, S. virgatum could be a natural candidate for developing well-accepted radioprotectant products capable of treating γ-irradiation-induced male infertility.

The influence of the composition of algal detritus on nematode assemblages

A field-based experiment was conducted on a detritus-loaded beach from the south coast of the British Isles (Poole Harbour) to investigate the decay rates of different combinations of algal detritus and their associated nematode assemblages. Ten algal mixture treatment combinations (monocultures with all possible 2 or 3 mixed algal treatments) of three different species of green (Chlorophyta), brown (Phaeophyta), and red (Rhodophyta) algae were used to determine how the diversity of decaying algal detritus affects the associated nematode assemblage composition and structure. Our results indicated that nematode density, diversity, and assemblage composition differed significantly among the different algal treatments. The nematode densities and genera richness were significantly higher in the mixed algal treatments compared to those in the algal monoculture treatments. The loss of seaweed dry weight varied significantly among the algal detritus treatments with which included brown algae tending to decay at a slower rate than others. These results indicate different type of macroalgae detritus could offer different nutrient input and that encourage different dominant nematode species and composition.

Potential to resist biological contamination in marine microalgae culture: Effect of extracellular substances of Nannochloropsis oceanica on population growth of Euplotes vannus and other protozoa

The commercially important marine microalgae Nannochloropsis oceanica is easily ingested by protozoan predators during large-scale cultivation. However, investigations into the effect of microalgae on the growth of protozoa are scant. A feeding experiment was conducted with Euplotes vannus grazing on different concentrations of N. oceanica. The ciliate population was significantly lower in the high concentration of algae than that in the low or medium algal concentration treatments. The density of ciliates cultured in algae filtrate media was significantly lower than that in lysate media and the blank control. Furthermore, the algal cell filtrate was added to three other protozoan populations, and they all gradually lost their ability to move and their body shape changed. This study investigated the interactions between N. oceanica and protozoan predators and provides insight on using microalgal extracellular substances to control biological contamination in the future.

Suitability of an Algal Biofuel Species, Scenedesmus acutus, as a Fertilizer for Growth of Conventional and Genetically Modified Lettuce

Nitrogen (N) and phosphorus (P) are important elements for global food production, but these nutrients cause pollution in water bodies without proper management. Furthermore, P is a finite resource with geologic reserves that are geographically restricted. Thus, sustainable use of P in agriculture has been the subject of much research over the past decade. This study jointly examines two examples of potential sustainability measures to address nutrient challenges: improved crop varieties and use of recycled fertilizers. We tested the effectiveness of dried biomass of a freshwater alga (Scenedesmus acutus) as a fertilizer with conventional lettuce [Lactuca sativa cv. Conquistador; WT (wild-type)] and genetically modified lettuce of the same variety that was transformed for improved nutrient-use efficiency [(type I Arabidopsis Vacuolar Pyrophosphatase (AVP1)]. In greenhouse conditions, we measured yield, soil nutrient content and losses, and soil P fractions after application of dried S. acutus biomass at different rates, with and without supplemental additions of conventional fertilizer. Yield was higher with commercial fertilizer compared with algal fertilizer, and AVP1 lettuce consistently produced better yield than the conventional lettuce with both fertilizer types, although the effect was stronger with the algal treatments. Soil P was mostly sequestered in the pools of NaHCO3-extractable organic P, NaOH-extractable organic P, and HCl-extractable P, which are poorly available. Although the algal fertilizer was ineffective in supporting short-term growth, the P was retained in the soils, which may improve soil fertility in the long term.

In vitro ruminal fermentation and methane inhibitory effect of three species of microalgae

In this study, in vitro ruminal fermentation, anti-methanogenesis, and ammonia formation of two autotrophic algae [Nannochloropsis gaditana (NG), Phaeodactylum tricornutum (PT)], and one heterotrophic alga [Schizochytrium sp. (SS)] were investigated. The experimental diets consisted of a hay-concentrate basal diet (BD; 200 mg dry matter) supplemented with (1) no algae (just BD), (2) 40 mg of dried NG (BD + NG), (3) 40 mg of dried PT (BD + PT), and (4) 14 mg of dried SS. In total, 48 samples (four algal treatments × two replicates × three runs × two cows) were incubated for 24 h using the Hohenheim gas test method. All three algae decreased (P < 0.05) the production of short-chain fatty acids and protozoal abundance (both adjusted in amount to BD) as compared with BD. Ammonia formation of BD + NG and BD + PT was 1.2- and 1.1-fold of values in BD, respectively. The BD + NG diet enhanced the proportions of isobutyrate, valerate, and isovalerate at cost of acetate proportion of total short-chain fatty acids, whereas the BD + PT diet promoted the proportions of propionate and valerate at cost of acetate. None of the microalgae affected in vitro methane formation. In conclusion, these algae showed a very poor fermentability and no anti-methanogenic effect in vitro.

Effects of feeding with red algae (Laurencia caspica) hydroalcoholic extract on antioxidant defense, immune responses, and immune gene expression of kidney in rainbow trout (Oncorhynchus mykiss) infected with Aeromonas hydrophila

In this study, the effects of hydroalcoholic extract of red algae (Laurencia caspica) at different levels were evaluated on antioxidant defense, innate immune responses, and expression of immune genes in rainbow trout (Oncorhynchus mykiss). A total of 750 rainbow trout (39.43 ± 0.44 g) were randomly assigned to five treatments with three replicates (50 fish per replicate) in 15 ponds and reared for 8 weeks. Fish samples were fed a diet containing different levels of algal extract (0, 5, 10, 15, and 20 g extract per kg of basal diet). At the end of feeding period, the fish were challenged with Aeromonas hydrophila and fish mortality was recorded over a 10-day period. To evaluate the antioxidant and immune parameters, fish were sampled at day 0, end of weeks 4 and 8, and after bacterial challenge. Expression of immune genes (IL-1β, lysozyme II, Complement C3, and TNFα) was also examined after bacterial challenge. Results indicated that application of algal powder in fish diet improved lysozyme activity, complement system, and immunoglobulin levels of extract fed-fish compared to control group (p < .05). The activities of antioxidant enzymes (catalase, glutathione peroxidase, and superoxide dismutase) were affected by the algal extract, with increasing levels in algal extract treatments compared to control fish (p < .05). According to the results, relative expression of target genes showed significant increases in 1.5% treatment compared to the other and control groups (p < .05). At the end of 10-day fish exposure to A. hydrophila, fish survived significantly higher in treatments received the algal extract than the control group, with the highest survival rate recorded in 1.5% algal extract (p < .05). According to the effective results of L. caspica extract on stimulating the immune system and increasing fish resistance to A. hydrophila, it is recommended to use 1.5% of this algal extract in rainbow trout diets.

Effect of heterocystous nitrogen-fixing cyanobacteria against rice sheath blight and the underlying mechanism

Rice sheath blight causes serious damage to rice crops in China. The most common practice for rice sheath blight control is still chemical treatment, an environmentally unfriendly way. Studies have demonstrated the use of nitrogen-fixing cyanobacteria to prevent crop diseases as well as to improve soil fertility and crop productivity. However, little information is available on the biocontrol of rice sheath blight using cyanobacteria. Therefore, the objective of the present study was to screen and evaluate the biocontrol effect of nitrogen-fixing cyanobacteria against the disease through microchamber and microarea experiments. Based on the results of the microchamber experiment, three strains (SCAU04, SCAU15, and SCAU26) out of nine nitrogen-fixing cyanobacterial strains with a significant inhibition (>80%) on rice sheath blight were selected. Further, microarea experiments during two seasons demonstrated the highest disease control efficacy (54.5%) on day 20 with SCAU26 treatment. Moreover, the algal treatments significantly promoted root length, underground biomass, and number of grains per panicle. SCAU04 and SCAU26 treatments significantly improved the rice theoretical yield and significantly (P < 0.05) enhanced soil potassium content compared with the control group without algal treatment. The extract of SCAU04, SCAU15, and SCAU26 algal cells inhibited the mycelial growth of R. solani (inhibition rate; 90.12%, 78.33%, and 89.87%, respectively). Based on gas chromatography–mass spectrometry results, eight metabolites were selected and evaluated for their activity against R. solani. Among them, seven inhibited R. solani growth; diisooctyl adipate showed the highest inhibitory effect. All three cyanobacteria produced the phytohormones salicylic acid, auxins, and cytokines. The salicylic acid and trans-zeatin-riboside contents of SCAU04 were 3654.74 ng g−1 and 5266.67 ng g−1, respectively. The isopentenyladenine content of SCAU26 reached 2839.98 ng g−1. Morphological and molecular analysis identified the best two strains SCAU04 and SCAU26 as Nostoc piscinale and Anabaena variabilis, respectively. To conclude, our findings indicate that cyanobacteria produce bioactive substances to inhibit R. solani, secrete phytohormones to promote plant growth and induce plant disease resistance, and improve soil nutrient content to support plant growth.

Contact- and Water-Mediated Effects of Macroalgae on the Physiology and Microbiome of Three Indo-Pacific Coral Species

Competitive interactions between corals and macroalgae play an important role in determining benthic community structure on coral reefs. While it is known that macroalgae may negatively affect corals, the relative influence of contact- versus water-mediated macroalgal interactions on corals—such as via an influence on coral-associated microbiomes—is less well understood. Further, the impacts of macroalgae on corals that have persisted in a heavily urbanized reef system have not been explored previously. We examined the effects of the macroalgae Lobophora sp. and Hypnea pannosa on the physiology and microbiome of three Indo-Pacific coral species (Merulina ampliata, Montipora stellata, and Pocillopora acuta) collected from Singapore’s highly urbanized reefs, and compared how these effects varied between direct contact and water-mediated interactions. Direct contact by Lobophora sp. caused visible tissue bleaching and reduced Fv/Fm in all three coral species, while direct contact by H. pannosa only led to slight, but significant, suppression of coral Fv/Fm. No detrimental effects on coral physiology were observed when corals were in close proximity to the macroalgae or when in direct contact with algal mimics. However, both direct contact and water-mediated interactions with Lobophora sp. and H. pannosa altered the prokaryotic community structures in M. stellata. For M. ampliata and P. acuta, the changes in their microbiomes in response to algal treatments were more strongly influenced by the source reefs from which the coral colonies were collected. In particular, coral colonies collected from Kusu Island had proportionately more initial abundances of potentially pathogenic bacteria in their microbiomes than those collected from Pulau Satumu; nevertheless, coral fragments from Kusu Island had the same physiological responses to macroalgal interactions as corals from Pulau Satumu. Overall, our results reveal that, for the species tested, the coral microbiomes were sensitive to both direct contact and water-mediated interactions with macroalgae, while coral physiology was only compromised when in direct contact. Further, the presence of high levels of potentially pathogenic bacteria in some of the coral samples did not lead to the corals being more susceptible to impacts from macroalgae.

Improvement of Growth, Physiology and Antioxidant System of Vicia faba by Algal Treatments

Improvement of Growth, Physiology and Antioxidant System of Vicia faba by Algal Treatments

Effects of the harmful algae, Alexandrium catenella and Dinophysis acuminata, on the survival, growth, and swimming activity of early life stages of forage fish

The effects of co-occurring harmful algal blooms (HABs) on marine organisms is largely unknown. We assessed the individual and combined impacts of the toxin producing HABs, Alexandrium catenella and Dinophysis acuminata, and a non-toxin-producing HAB (Gymnodinium instriatum) on early life stages of two estuarine fish species (Menidia beryllina and Cyprinodon variegatus). Lethal (i.e. time to death) and sublethal (i.e. growth, grazing rate, and swimming activity) effects of cultured HABs were investigated for eleutheroembryo and larval life stages. Mixed algal treatments (i.e. A. catenella and D. acuminata mixtures) were often equally toxic as A. catenella monoculture treatments alone, although responses depended on the fish species and life stage. Fish exposed to toxin producing HABs died significantly sooner (i.e. <1–3 days) than controls. Significant differences in sublethal effects were also found between fed controls and toxic HAB treatments, although responses were often similar to G. instriatum or starved controls. Collectively, the results demonstrate that HABs may reduce fish productivity and fitness.

Algal application as a biological control method of root-knot nematode Meloidogyne incognita on cucumber under protected culture conditions and its impact on yield and fruit quality

This study was conducted during seasons 2016 and 2017 to control the root-knot nematode Meloidogyne incognita in cucumber, cultivated in infected soil, using some algal treatments under greenhouse conditions, at Kaha Farm, Qaluobia Governorate, Egypt. Six algal treatments were tested: two foliar applications of Spirulina and Amphora, two drenched soil applications of Spirulina and Amphora, two treatments using Spirulina, as spraying and drenching, and Amphora, as spraying and drenching, in addition to the Rugby nematicide (10% Ebufos, at the rate of 5 g/m2) and control. Rugby was applied by a soil prepared in its experimental units. After 15 days from transplanting, the algal extract treatments were applied twice monthly for 3 months. The same concentration (2 g/l) of both types of algae was applied in both foliar and drench treatments. The control was sprayed only by water. The results indicated that the soil drenched with Amphora or Spirulina extracts had significant increments in vegetative growth, yield, and fruit quality. In contrast, the control plants had the lowest values in all criteria. Amphora (sprayed with soil drenched) treatment gave 2.5 and 2.69 folds the control in marketable yield in 2016 and 2017 seasons, respectively. The combination of sprayed and soil drenched with Amphora was more effective in nematode’s control or in enhancing plant resistance for nematode as shown at most nematode parameters, especially the rate of nematode reproduction factor (RF), which reached 0.42 and 0.45 in both seasons, respectively. It had insignificant differences compared with the nematicide. Therefore, using algae for the biological control of root-knot nematodes is recommended, especially in sustainable agriculture for maintaining the soil and improve fertility.

Combined Effects of Drift Macroalgal Bloom and Warming on Occurrence and Intensity of Diel-Cycling Hypoxia in a Eutrophic Coastal Lagoon

Recently, eutrophication-induced macroalgal bloom and elevating temperature caused by climate change have become major threats to benthic organisms by causing coastal hypoxia. However, combined effects of drift macroalgae and warming on the occurrence and intensity of hypoxia are not well understood, although these anthropogenic stressors have co-occurred. We conducted 10 seasonally replicated 7-day algal enclosure/exclosure experiments at a shallow coastal zone in the eutrophic Nakaumi Lagoon, western Japan, to evaluate the combined effects of drift algae and water warming on occurrence and intensity of diel-cycling hypoxia. Experimental units were 1 × 1 m plots of the sandy bottom fenced within 1 m height with plastic mesh that excluded or included drift algae, with automated dissolved oxygen (DO) sensors deployed at the sediment surface. DO fluctuated over a diel cycle for both algal treatments, and algal presence and elevated temperature additively amplified the diel DO cycle. Algal presence and elevated temperature synergistically increased the occurrence and intensity of diel-cycling hypoxia. The occurrence of hypoxia, including anoxia, increased non-linearly in the presence of algae when mean water temperature exceeded ~ 25 °C, whereas such drastic increase in the hypoxia occurrence was not observed in the absence of algae. Furthermore, the daily minimum DO declined more steeply with warming under algal presence than the absence of algae. These results suggest that coastal areas in the lagoon are now seriously threatened by simultaneous progressions of eutrophication linking to algal bloom and global warming.

A tale of two algal blooms: Negative and predictable effects of two common bloom-forming macroalgae on seagrass and epiphytes

Recent evidence suggests macroalgal blooms may play a role in the worldwide decline in seagrass, but the shape of the functional relationship between seagrass health and dominant bloom-forming macroalgae is poorly characterized. We tested whether the impact of varying abundances of two cosmopolitan bloom-forming macroalgal genera caused linear/quasi-linear or sudden threshold changes in measures of eelgrass, Zostera marina, meadow health. We conducted two caging experiments in a shallow Z. marina bed (∼1 m depth) in Bodega Harbor, California, USA where we maintained six densities within the range of natural abundances of macroalgae, Ulva (0–4.0 kg m−2) and Gracilariopsis (0–2.0 kg m−2), as well as uncaged controls over a 10-week period. Shoot density, blade growth, and epiphyte load were measured every two weeks and algal treatments reset. We did not find support for threshold transitions between algal abundance and measures of seagrass bed health using sigmoidal and broken-stick regression analyses for each data set; these models are commonly used to identify threshold patterns in ecological shifts. Instead, final measurements of shoot density and epiphyte load were best modelled as linear or slightly non-linear declines with increasing Ulva abundance. A negative linear relationship also existed between shoot density and Gracilariopsis abundance and a trend towards linear negative effects on epiphyte load. The similar shape of these functional relationships across different types of algae suggests the relationship may be generalizable. At algal abundances that are commonly observed, we found smooth and predictable negative impacts to Z. marina by decline in shoot density and potential impacts to food webs by loss of epiphytes rather than sudden threshold shifts or “ecological surprises”. Our work contrasts with the growing body of literature suggesting highly non-linear shifts in response to human impact; thus, it is important to broaden understanding of shifts to more than just pattern but to the processes that drive different patterns of shifts.