Chaetoceros Muelleri Research Articles

Potential Use of Algae and Seaweed Extracts as Protection Against Peach Leaf Curl

Abstract Plant pathogenic fungi are a major cause of plant diseases, contributing significantly to the global decline in food production. Their proliferation results in substantial crop losses, fruit and vegetable deterioration, reduced food accessibility, and billions of dollars in economic losses annually. While synthetic chemical fungicides are commonly used to combat fungal diseases, their environmental impact is concerning. Marine algae provide a sustainable alternative, offering diverse compounds with industrial applications and presenting an eco-friendly solution. Taphrina deformans is responsible for peach leaf curl, a widespread disease in peach trees that can severely impact crop productivity and tree lifespan. Seaweeds and algae, encountering various biological interactions and extreme abiotic conditions, have evolved defense mechanisms, including the production of biologically active substances. In our study, we investigated the efficacy of water extracts from six algae (Nannochloropsis sp., Tetraselmis chuii, Chaetoceros muelleri, Thalassiosira weissflogii, Tisochrysis lutea, Chlorella vulgaris), four seaweeds (Palmaria palmata, Chondrus crispus, Ascophyllum nodosum), and one cyanobacterium (Arthrospira platensis) at two different concentrations (1% and 3%) in suppressing the outbreak of peach leaf curl disease in vivo on peach trees. The spray was applied twice in spring just before budbreak. Algae and seaweed extracts showed significant suppression of peach leaf curl outbreaks on peach trees compared to controls. Following the application of water extract of Chlorella vulgaris at both concentrations, the lowest incidences of symptomatic disease expression were observed (1.00 ±0.00% and 0.25 ±0.50%). Algae and seaweed extracts demonstrate potential in controlling leaf curl disease in peach trees.

Assessing new microalgae species as potential feed for bivalve spat in nursery culture

ABSTRACT Microalgae remains a primary food source for hatchery and nursery culture of juvenile bivalves. However, there is a mismatch between the characteristics of the microalgae currently used in nursery culture and the feeding abilities and nutritional requirements of juveniles of some bivalve species, such as the green-lipped mussel, Perna canaliculus. Therefore, there is a need to identify new species of microalgae for this purpose that have favourable cell size, good growth performance under culture conditions and appropriate nutritional content for juvenile bivalves by using these characteristics as primary selection criteria. In this study, the growth performance under standard culture conditions of four microalgae species (Chrysochromulina camella, Gymnodinium simplex, Pyramimonas parkeae and Stephanodiscus niagarae) which are of a sufficiently large cell size to meet the needs of juvenile mussels (i.e. 10–20 µm size range) were tested in comparison to three commonly cultured commercial species (Chaetoceros muelleri, Diacronema lutheri and Tisochrysis lutea). Results show that G. simplex, S. niagarae and the two strains of P. parkeae (P. parkeae (C) and P. parkeae (I)) can achieve similar biomass as the reference species in the intermediate (1 L) culture stages despite the large difference in cell densities. The poor growth of C. camella in F/2 media indicates a necessity of determining its appropriate culture conditions before further assessing its suitability as a nursery feed for juvenile bivalves. The proximate analysis of S. niagarae, G. simplex and P. parkeae (I) reveals nutritional profiles conducive to spat development. However, the P. parkeae (C) strain contained low carbohydrate content, suggesting inferior nutritional value compared to the P. parkeae (I) strain, showing that variants of the same species can have different biochemical composition and suggesting the former might have limited suitability for feeding in nursery culture. The findings indicate that G. simplex, S. niagarae and P. parkeae (C) hold sufficient promise as spat feed in nursery culture to warrant further testing to confirm their efficacy as live microalgal feed for bivalve spat.

Effect of diet on larval settlement, growth, and spat survival of the oyster Crassostrea gigas (Thunberg, 1793)

This study aimed to assess the impact of microalgal concentrations in diets on the settlement and metamorphosis stages of pediveliger larvae and spat of Crassostrea gigas oysters. Diets containing microalgal concentrations of 8, 12, and 16×104 cells mL-1 were administered for seven days during the larval settlement phase of pediveliger larvae. In the metamorphosis and postlarval cultivation phases, diets with microalgal concentrations of 8, 16, 24, and 32×104 cells mL-1 and a control group without food were tested for 14 and 21 days, respectively. Growth, yield, and survival were assessed every seven days. The diet comprised 30% Isochrysis galbana and 70% Chaetoceros muelleri microalgae. In the metamorphosis phase, the results revealed no significant differences in larval metamorphosis rate and survival across the tested diets. The concentrations exhibited similar survival in the spat with an initial average shell height of 0.657 ± 0.05 mm, with a significant difference only in growth. In the spat with an initial average shell height of 0.830 ± 0.12 mm, no differences in survival were observed among the tested concentrations. We concluded that diets of 12 and 16×104 cells mL-1 provide high rates of larval metamorphosis and spat yield during the larval settlement and metamorphosis phases. During the spat cultivation phases, diets of 32 and 24×104 cells mL-1 could optimize the cultivation time and yield of C. gigas spat in the laboratory. However, when considering survival alone, no advantage was found in providing a diet with a microalgal concentration above 8×104 cells mL-1 across all C. gigas oyster cultivation phases.

Nutritional value of a novel EMS-induced cell wall-defective strain of Saccharomyces cerevisiae yeast for Pacific oyster (Magallana gigas) juveniles

The difficulties and high costs of live microalgae production have driven the search for alternative diets in bivalve aquaculture. The baker's yeast (Saccharomyces cerevisiae) represents a promising, cost-effective, high-quality protein for aquaculture. However, its application is restricted by poor digestibility due to its thick, rigid cell wall. Previously, we observed that the deletion of mnn9 gene in S. cerevisiae, leading to defective mannan synthesis and increased β-glucan exposure, enhances growth and immune response in Magallana gigas oysters. Nevertheless, using ∆mnn9 in aquaculture is not feasible due to restrictions on genetically modified organisms (GMO) containing antibiotic-resistance genes. This study aimed to create a non-GMO cell-wall defective yeast mutant (JH40) via ethyl methanesulfonate (EMS) mutagenesis and evaluate its nutritional value for M. gigas juveniles. Phenotypical differences between wild-type S. cerevisiae (WT), ∆mnn9, and JH40 were characterized using fluorescein isothiocyanate (FITC)-labeled lectin analysis, microscopy, cell diameter measurements, growth curves, and osmosensitivity tests. The nutritional value of a microalgae-based diet (Chaetoceros muelleri:Tisochrysis lutea, 50:50 based on dry weight) and its 50% substitution with JH40 or WT was assessed over 21 days in M. gigas juveniles. A complementary test also explored higher substitution levels (63%, 75%, and 100%) of the based diet with JH40 and the addition of extra JH40 (+25 %) in the 63% and 75% replacement diets. Results indicated that JH40 forms clumps, grows slower than the WT, has a larger cell diameter, higher binding affinity to WGA and LEL lectins than the WT, and is highly sensitive to hypo-osmotic stress, which are characteristics of cell-wall defective yeasts. Oysters fed a diet with 50% JH40 substitution showed significantly higher growth compared to those fed the WT-containing diet. JH40 could replace 50% of the algal diet without significantly affecting oyster growth and survival. However, higher inclusion levels of JH40 (62 %, 75 %, and 100 %) did not achieve the oyster growth observed with the algae-based diet, even with additional yeast. These findings are attributed to the limited polyunsaturated fatty acid content in yeast cells. Further research on dosing and administration frequencies is needed to evaluate the immunostimulatory potential of JH40.

Investigating the role of allelochemicals in the interaction between Alexandrium monilatum and other phytoplankton species

Species of the dinoflagellate genus Alexandrium can release bioactive extracellular compounds with allelopathic effects (e.g., immobilization, inhibition of growth, photosynthesis or lysis) towards other phytoplanktonic organisms. In the lower Chesapeake Bay, Virginia, US, succession or co-occurrence of blooms of Akashiwo sanguinea, Margalefidinium polykrikoides and the goniodomin-producing A. monilatum tend to be common during summer months, however the allelopathic potential of A. monilatum, and how it may affect bloom dynamics, has not be studied. We used a rapid fluorescence-based bioassay as well as flow cytometry and an assessment of immobilization to determine the potential effects of A. monilatum culture supernatants on M. polykrikoides, A. sanguinea and the diatom Chaetoceros muelleri (included as a reference strain). In addition, we also investigated the effects of standards of known A. monilatum toxins goniodomin A (GDA) and GDA seco-acid (GDA-sa). Exposure of C. muelleri to culture supernatants from two different strains of A. monilatum resulted in an inhibition of the maximum quantum yield of the photosystem II (Fv/Fm) and cell lysis of the diatom, with strain-specific variation observed, highlighted by a 30-fold difference in the effective concentration resulting in 10 % inhibition (EC10) and 2-fold difference in the lethal concentration resulting in 50 % mortality (LC50) between the two A. monilatum strains tested. Exposure of M. polykrikoides to A. monilatum culture supernatants resulted in a decrease in motility (at ≥ 500 eq. cells mL-1) along with a decrease in Fv/Fm (at ≥ 1,500 cells mL-1) and altered cellular morphology (at ≥ 3,500 eq. cells mL-1). No effect was observed when A. sanguinea was exposed to A. monilatum culture supernatants (at the concentrations tested in these studies). When M. polykrikoides was exposed to the GDA standard, its Fv/Fm (at ≥ 1,951 nM) and motility (at ≥ 390 nM) decreased, and its morphology (at ≥ 975 nM) was modified. The study of supernatant time- and temperature-stability, and the absence of a relationship between observed effects and goniodomin concentrations suggested the presence of additional unknown allelochemicals distinct from goniodomins, as has been observed for other Alexandrium species. Immobilization of M. polykrikoides by A. monilatum culture supernatants and GDA standard in laboratory-based exposure experiments may indicate that A. monilatum has a competitive advantage when both species co-occur in the Chesapeake Bay and this warrants further testing.

Studies on embryo development and larval feeding of clam Paphia textile

The present study investigated the embryonic development, growth, metamorphosis, locomotory patterns, and feeding behaviors of Paphia textile larvae, offering dietary suggestions based on observed patterns. The larvae were subjected to a dietary regimen consisting of nine microalgae species at various developmental stages (1, 4, 7, 10, 13, and 16 days post-hatching). One hour after each feeding session, their feeding patterns were carefully documented. To assess digestion, larvae that had consumed the microalgae were filtered, rinsed, and placed in filtered seawater. The embryonic development of P. textile encompassed distinct stages, including the fertilized egg, emergence of the first and second polar bodies, progression through the 2–32 cell stage, morula stage, blastula stage, gastrula stage, trochophore stage, and ultimately the D-larvae stage. Movement patterns revealed that the larvae primarily utilized their cilia for locomotion and feeding. From a transverse perspective, they moved clockwise, tracing an irregular circular path. Vertically, they exhibited spiral movements, ascending or descending as needed. As they entered the late stage, they transitioned to using reciprocal expansion of their axe feet for crawling and filtering food through their gills. Throughout their development, the larvae were fed a variety of microalgae species, including Chlorella vulgaris, Nannochloropsis oculata, Pavlova viridis, Dicrateria zhanjiangensis, and Isochrysis galbana. At 4 days old, they began consuming Dunaliella salina, and at 7 days, they incorporated Platymonas subcordiformis into their diet. By 10 days of age, they had expanded their food choices to include Chaetoceros muelleri. However, it was noted that larvae frequently suffered from indigestion or incomplete digestion when fed excessive amounts of C. vulgaris and N. oculata. Therefore, it is recommended to commence the larval culture of P. textile using P. viridis, D. zhanjiangensis, and I. galbana as the primary dietary sources. Furthermore, a feeding strategy emphasizing small, frequent meals is recommended to promote optimal digestion and larval health.

Characterization of Selected Microalgae Species as Potential Sources of Nutrients and Antioxidants.

Microalgae are exceptional organisms from a nutritional perspective, boasting an array of bioactive compounds that have long justified their incorporation into human diets. In this study, we explored the potential of five microalgae species: Nannochloropsis sp., Tetraselmis chuii, Chaetoceros muelleri, Thalassiosira weissflogii, and Tisochrysis lutea. We conducted comprehensive analyses of their nutritional profiles, encompassing protein content, individual amino acid composition, mineral and trace element levels, fatty acid profiles (including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs)), polyphenol compositions, and vitamin B content. The antioxidant activity of the ethanolic extracts was evaluated using two methods: ABTS and DPPH radical scavenging assay. The total protein content of the microalgae ranged from 34.09 ± 0.39% to 42.45 ± 0.18%, with the highest concentration observed in T. weissflogii. Essential amino acids such as histidine, threonine, lysine, valine, isoleucine, leucine, phenylalanine, and methionine were present in concentrations ranging from 0.53 ± 0.02 to 12.55 ± 2.21 g/16 g N. Glutamic acid emerged as the most abundant amino acid, with concentrations ranging from 6.73 ± 0.82 to 12.55 ± 2.21 g/16 g N. Among the microalgae species, T. chuii exhibited the highest concentrations of calcium (Ca) and manganese (Mn), while C. muelleri showed prominence in magnesium (Mg), sodium (Na), and iron (Fe). T. weissflogii stood out for its potassium (K) content, and T. lutea contained notable amounts of copper (Cu), zinc (Zn), and lead (Pb). Regarding fatty acid profiles, Nannochloropsis sp. and T. chuii were predominantly composed of SFA, while C. muelleri and T. weissflogii were rich in MUFA. PUFAs dominated the fatty acid profile of T. lutea, which also exhibited the most diverse range of polyphenolic substances. We also analyzed the B vitamin content, with T. lutea displaying the highest concentrations of niacin (B3) and riboflavin (B2). Antioxidant activity was confirmed for all microalgae tested using DPPH and ABTS radical IC50 (mg/mL) converted to Trolox equivalent (TEAC). These findings underscore the substantial potential of the examined microalgae species as sources of biologically valuable substances characterized by rapid growth and relatively undemanding cultivation conditions.

Effects of the toxic dinoflagellate, Alexandrium pacificum, on the marine diatom, Chaetoceros muelleri, and mussel (Perna canaliculus) sperm and hemocytes

Harmful algal blooms (HABs) of Alexandrium pacificum have affected the Marlborough Sounds in New Zealand since 2010, posing a threat to green-lipped mussel (GLM, Perna canaliculus) farming. Previous studies have shown A. pacificum has negative effects GLM embryos and larvae. To further investigate these toxic mechanisms, in vitro bioassays were conducted on GLM spermatozoa, hemocytes, and the diatom, Chaetoceros muelleri. The three cell types were exposed to several treatments of A. pacificum for 2 h and responses were measured using flow cytometry and pulse amplitude-modulated fluorometry. Significant spermatozoa mortality was recorded in treatments containing A. pacificum cells or fragments, while hemocyte and C. muelleri mortality was recorded in cell-free treatments of A. pacificum which contained paralytic shellfish toxins (PSTs). Variation in sensitivity between cell types as well as the sublethal effects observed, emphasise the diverse toxic mechanisms of A. pacificum on co-occurring species in the environment.

EVALUATION OF THE EFFECT OF AUXINS ON GROWTH AND BIOCHEMICAL PARAMETERS OF CHAETOCEROS MUELLERI

Background. The study of microalgae cultivation process is not only related to obtaining a wide range of biologically active substances. With the development of mariculture, some species of microalgae (including Chaetoceros muelleri) are of interest as food for mollusks, arthropods and holothuria. The aim of this study was to evaluate the effect of auxin hormones on quantitative and qualitative parameters Chaetoceros muelleri accumulative cultivation. Materials and methods. The object of research was the culture of microalgae Chaetoceros muelleri. The duration of the experiment was 7 days. Indole-3- butyric and indole-3-acetic acids were used for growth stimulation. The microalgae were cultured in monoculture, under constant conditions. 0.1; 0.2; 0.4; 0.6; 1.0 ×10-5mol phytohormones concentrations were added to the cultivation medium of the experimental groups. The control group was cultured without phytohormones addition. Results. It was shown that indole-3-acetic acid in concentrations from 0.2 to 0.5×10-5 mol had a positive effect on the growth of algal culture. Auxins at optimum concentration had a positive effect on lipid accumulation in the algal culture. It was found that indole-3-butyric acid increased the carbohydrate content in the culture on the 3rd day of culturing Chaetoceros muelleri. At the same time, under the action of indole-3-butyric acid, the highest content of carbohydrates. Conclusion. The obtained data showed that the studied auxins had a positive effect on Chaetoceros muelleri dynamics growth. The possibility of using auxin series phytohormones to stimulate the growth of the microalga Chaetoceros muelleri in an accumulative monoculture has been established by this study.

Carry-Over Effects of Broodstock Conditioning on the Salinity Tolerance of Embryos of the New Zealand Geoduck (Panopea zelandica)

The New Zealand geoduck (Panopea zelandica) has seen considerable interest from the NZ aquaculture industry. A major bottleneck in culturing P. zelandica is early life stages mortality (e.g., embryo). Therefore, in this study, we investigated the embryonic performance and their transition to the first feeding larval stage (D-veliger) under different salinities (26, 30, 32, and 35 ppt) of four different offspring groups generated from broodstock being fed different ratios (25 : 75, 50 : 50, 60 : 40, and 75 : 25) of the haptophyte Tisochrysis lutea (formerly Isochrysis galbana) (ISO) and the diatom Chaetoceros muelleri (CM) during gametogenesis. Broodstock within all diet ratio treatments successfully conditioned, producing viable embryos. Average egg size ranged between 75 and 80 µm and was not affected by the diet ratios of the broodstock. Survival 48 hr postfertilization, D-veliger larvae yield, and incidence of abnormalities depended on both the embryo rearing salinity and broodstock feeding ratios. The combined salinity of 32−35 ppt and a feeding ratio of 50 : 50 and 60 : 40 (ISO:CM) had the highest survival of embryos (56.0%–77.5%), highest production of D-veliger larvae (>65%), and lowest incidence of abnormalities within D-Veliger (<47%). The size of the larvae decreased with decreasing salinities, with the largest found at 35 ppt (101.22 ± 0.49 µm in shell length). Embryos and larvae did not survive at salinity 26 ppt. These results suggest that diet during gametogenesis can play a role on the offspring ability to cope with environmental stressors at least during the critical first few days after fertilization. These findings provide important information on transgenerational effects due to broodstock diet, especially during the early life stages.

Effects of Nutrient Source, Temperature, and Salinity on the Growth and Survival of Three Giant Clam Species (Tridacnidae).

The habitats of giant clams are undergoing environmental changes, and giant clam populations are declining. The present study was conducted to facilitate clam conservation. We conducted three 18-week trials to investigate the effects of nutrient, temperature, and salinity on the growth performance and survival rates (SRs) of juvenile Tridacna noae, adult Tridacna crocea, and subadult Tridacna derasa, respectively. Regarding nutrient sources, no significant differences were observed in shell length gain, specific growth rate, or SR between clams fed with Chaetoceros muelleri or commercial feed (hw nanotip) and those in a control group (juvenile phototrophs). Regarding temperature, clams cultivated at 27 °C exhibited significantly better growth performance and SR than did those cultivated at 19 °C or 31 °C (p < 0.05). By week 6, all clams in the 19 °C and 31 °C groups had died, indicating that suboptimal growth temperatures have severe adverse effects. Regarding salinity, clams cultivated at 34‱ exhibited significantly higher length gains and specific growth rates than did those cultivated at 20‱ or 25‱ (p < 0.05). SR was not significantly affected by salinity. Understanding how environmental factors affect giant clam populations may help researchers devise effective clam conservation strategies.

Ionic and nanoparticulate silver alleviate the toxicity of inorganic mercury in marine microalga Chaetoceros muelleri.

Toxicological effects of silver nanoparticles (SNPs) in different organisms have been studied; however, interactions of SNPs with other environmental pollutants such as mercury are poorly understood. Herein, bioassay tests were performed according to ΟECD 201 guideline to assess the toxic effects induced by mercury ions (mercury chloride, MCl) on the marine microalga Chaetoceros muelleri in the presence of SNPs or silver ions (silver nitrate, SN). Acute toxicity tests displayed that the presence of SNPs or SN (0.01mg L-1) significantly reduced the toxicity of MCl (0.001, 0.01, 0.1, 1, 10, and 100mg L-1) and increased the IC50 of MCl from 0.072 ± 0.014 to 0.381 ± 0.029 and 0.676 ± 0.034mg L-1, respectively. In the presence of SN or SNPs, the mercury-reducing effect on algal population growth significantly decreased. Considering the increase of IC50, the mercury toxicity decreased approximately 5.44 and 9.66 times in the presence of SNPs or SN, respectively. The chlorophyll a and c contents decreased at all exposures; however, the decrease by MCl-SNPs and MCl-SN was significantly less than MCl except at 1mg L-1. The lowering effect of MCl-SN on chlorophyll contents was less than MCl and MCl-SNPs. MCl exposure induced significant raises in total protein content (TPC) at concentrations < 0.01mg L-1, with a maximum of ~ 70.83% attained at 100mg L-1. The effects of MCl-SNPs and MCl-SN on TPC were significantly less than MCl. Total lipid content (TLC) at all MCl concentrations was higher than the control, while at coexposure to MCl-SN, TLC did not change until 0.01mg L-1 compared with the control. The effects of MCl-SN and MCL-SNPs on TPC and TLC were in line with toxicity results, and were significantly less than those of MCl individually, confirming their antagonistic effects on MCl. The morphological changes of algal cells and mercury content of the cell wall at MCl-SN and MCl-SNPs were mitigated compared with MCl exposure. These findings highlight the mitigatory impacts of silver species on mercury toxicity, emphasizing the need for better realizing the mixture toxicity effects of pollutants in the water ecosystem.

Nutrient enrichment and probiotics for sea urchin Anthocidaris crassipina larvae in captivity to promote large-scale aquaculture.

Sea urchin contains physiologically active substances, such as amino acids and unsaturated fatty acids, and an important aquatic organism. Purple sea urchin, one of the common edible sea urchins, is an important aquatic product. In order to supply the vast seafood market, large-scale aquaculture of sea urchins is very important. The aim of this study was to optimize the rearing of theAnthocidaris crassipina larvae enhancing the nutrition by mixing feed to improve their growth and survival. The survival rate of Chaetoceros muelleri feeding alone is only 40%. If the survival rate is improved through nutrient enrichment, the large-scale aquaculture of larvae can be promoted. The experiment was divided into two parts. Experiment 1: Two types of commonly used microalgae, Isochrysis galbana tml (I), C. muelleri (C) and two types of probiotics, Rhodopseudomonas palustris (R), and Saccharomyces cerevisiae (S) were used in the.Feeding amounts are 5000, 10,000, and 20,000 cell mL-1, and the control group (N) did not eat. Experiment 2: C. muelleri 20,000 cell mL-1 was mixed with I. galbana tml, R. palustris (R)and S. cerevisiae (S) at 5000 and 10,000 cell mL-1. After the experiment, body length, body width, stomach length, rudiment length, rudiment length, body composition, digestive enzymes and survival rate were measured to evaluate the best feed. The results showed that the mixed feeding of C. muelleri 20,000 cell mL-1 and R. palustris 5000 cell mL-1 can achieve the best development and survival of larval embryos and can promote metamorphosis into juveniles in the shortest time. The research results will be applied to the large-scale aquaculture of A. crassipina larvae to promote the diversity of aquaculture.

Ecophysiological behaviour of different diatoms in response to copepod signals

ABSTRACT Phytoplanktonic communities have been moulded from a higher level in the food web by zooplankton predation. Diatoms, which are the major primary producers in present day oceans, have evolved many strategies to thrive in the presence of copepods, their predators. Chemical signals are released in the aquatic environment by microarthropods and elicit morphological, behavioural and/or physiological modifications in diatom cells which allow them to cope with predators. Other than the most studied effects of copepod signals on the release of toxins by diatoms, the role of chemical cues on growth and biology of non-toxic diatoms has been little investigated, although it may broaden our knowledge of co-evolutive physiological mechanisms. To examine the response of diatoms to copepod-derived signals, Phaeodactylum tricornutum, Chaetoceros muelleri and Cylindrotheca fusiformis (Bacillariophyceae) were grown in the presence of copepod cues. Physiological modifications occurred and differed in sign and magnitude between species: i) in P. tricornutum cell density was higher, and dry weight lower, suggesting energy allocation into cell division at the expense of lipid and protein quotas; ii) C. muelleri showed a very homeostatic behaviour; and iii) in C. fusiformis cell density was lower and lipid content higher, showing energy allocation into lipids, which likely act as deterrent to feeders. Copepod cues are here suggested to have ruled diatom species composition in the ocean by affecting species-specific growth performance and the energy allocation into macromolecules.

Targeted cultivation of diatoms in mariculture wastewater by nutrient regulation and UV-C irradiation.

Mariculture wastewater poses environmental challenges due to pollution and eutrophication. Targeted cultivation of diatoms in wastewater can help alleviate these issues while generating beneficial algae biomass, however reliable operating methods are lacking. We proposed a novel method for treating mariculture wastewater that employed UV-C irradiation and nutrient regulation to achieve targeted diatom cultivation. This study first examined growth of four diatom species (Nitzschia closterium, Chaetoceros muelleri, Cyclotella atomus, and Conticribra weissflogii) in mariculture wastewater. C. muelleri and C. weissflogii demonstrated better adaptability compared to N. closterium and C. atomus. Additionally, the growth and nutrient utilization of C. muelleri were studied under varying concentrations of silicate, phosphate, ammonium, and trace elements in wastewater. Optimal growth was observed at 500 μmol/L silicate, 0.6 mg/L phosphate, and 4 mg/L ammonium. Ammonium proved to be a more effective nitrogen source than urea and nitrate in promoting growth at this low level. Surprisingly, trace element supplementation did not significantly impact growth. Finally, this study utilized UV-C irradiation as a pre-treatment method for wastewater prior to nutrient adjustment, significantly enhancing the growth of C. muelleri. Overall, this study provides guidance on regulating key nutrients and pre-treatment method to optimize diatom biomass production from mariculture wastewater. This approach not only addresses environmental challenges associated with mariculture but also contributes to sustainable aquaculture practices through the recovery of valuable aquatic resources.

Comparison of live microalgae and Spray-dried algae powder effects on growth, digestive and antioxidant capacity of juvenile pearl oyster Pinctada maxima

The pearl production through the pearl oyster Pinctada maxima’s culture has developed slowly over the past decades due to over-fishing of wild populations and mass mortality at juvenile stages. Indoor farming is an alternative mode for P. maxima juvenile cultivation to improve survival rates. In pursuit of optimizing healthy management under the indoor farming mode, the objective of this investigation was to compare the growth performance, digestion, and antioxidant capacity of juveniles fed with different microalgae-based diets (live Isochrysis zhanjiangensis, Platymonas subcordiformis, Chaetoceros muelleri; and spray-dried I. zhanjiangensis, P. subcordiformis, C. muelleri powder). The juvenile survival rates fed with spray-dried microalgae powder (except C. muelleri powder) were not significantly different from those fed on live microalgae. However, the growth performance of juveniles fed with spray-dried microalgae powder could have been better than the live one. The digestive enzymatic activities were consistent with growth performance, and diets affected the antioxidant capacity. The spray-dried I. zhanjiangensis powder can serve as a substitute for live microalga in P. maxima juvenile indoor farming and is recommended under controlled conditions. The findings from this study would provide essential data to improve health management for P. maxima juveniles in indoor farming conditions.

Phycoremediation and valorization of hypersaline pickled mustard wastewater via Chaetoceros muelleri and indigenous bacteria

Hypersaline pickled mustard wastewater (PMW), a typical food wastewater with high nutrient content, was successfully bioremediated via the co-treatment of Chaetoceros muelleri and indigenous bacteria in this study. Chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus in 10 % PMW could be effectively reduced by 82 %, 90 %, 94 % and 96 %, respectively, after 12 days treatment. Oxygen species activities, malondialdehyde content, microalgal biomass, photosynthesis and extracellular polymeric substances were characterized during the treatment to determine the responses of the consortium when exposed to different concentration of PMW. Microbial community analysis demonstrated a significant increase in the relative abundance of Halomonas and Marinobacter in the 10 % PMW after 12 days treatment, which was beneficial for nutrients recycling by the diatoms. Meanwhile, C. muelleri was effective in reducing the relative abundance of potentially pathogenic bacteria Malaciobacter. In conclusion, the work here offers a promising and environmentally friendly approach for hypersaline wastewater treatment.

Effect of 4 microalgal diets on the proximal composition, chlorophyll concentration, and total carotenoid content in Artemia franciscana

Microalgae are the primary source of food for Artemia franciscana. In turn, Artemia serve as live food for various species in culture. The chemical composition of Artemia is of great importance because it affects the nutritional quality of the organisms produced in aquaculture systems. For this reason, the present study aimed to characterize the nutritional value, proximal composition, concentration of chlorophyll a and b, and total carotenoid content in the microalgae Thalassiosira weissflogii, Chaetoceros muelleri, Tetraselmis suecica, and Nannochloropsis sp., which were used to feed juvenile A. franciscana for 6 h. Artemia juveniles fed with these microalgae species exhibited higher concentrations of proteins, carbohydrates, lipids, chlorophyll a and b, and total carotenoids than those in the control. The organisms fed with Tetraselmis suecica presented the highest content of chlorophyll b, while those fed with Thalassiosira weissflogii and Chaetoceros muelleri showed the highest values of total carotenoids and chlorophyll a.

Effects of microalgae and stocking density on growth and survival rate of giant clam (Tridacna squamosa Lamarck, 1819) larvae

The present study aimed to evaluate the impact of microalgae mixture and stocking density on growth and survival rate of giant clam (Tridacna squamosa) at the veliger stage. In the first experiment, giant clam larvae of the D-stage were reared in the conical fiberglass tanks and fed with combinations of microalgae, including Chaetoceros muelleri and Isochrysis galbana (1:1), and C. muelleri, I. galbana and Nannochloropsis oculata, (1:1:1). One group of giant clam larvae without feeding was used as a control. The experiment was lasted for 7 days, until the Pediveliger stage with six replicate tanks. In the second experiment, the larvae (1 day post hatched, DPH) were reared at densities of 3, 5, 7 and 9 larvae mL-1 (so-called D3, D5, D7 and D9, respectively) for a period of 7 days. Each density was randomly assigned to 6 replicate tanks. The larvae were fed once a day with a mixture of C. muelleri, I. galbana and N. oculata, (5,000 cells/ml each type of algae). At 4DPH, extracted zooxanthelle (Symbiodinium microadriaticum) was seeded into the giant clam larvae at the concentration of 5,000cells/ml once a day.The results showed that larvae fed with C. muelleri, I. galbana and N. oculata (1:1:1) obtained the largest shell length (217.5 ± 3.1 µm), specific growth rate (SGR) 7.18 ± 0.34 (mean±SD) and the survival rate (31.5% ± 1.6%) (P<0,05). In addition, rearing densities significantly affected growth in shell length, SGR and survival rate in giant clam larvae. Of which, the larvae at D3 gained the highest shell length, SGR and survival rate. Meanwhile, the larvae at D9 had the lowest shell length, SGR and survival rate. There was no significant difference in larval survival rate between D3 and D5. Therefore, it is suggested that in the hatchery giant clam larvae reared at 5 larvae mL-1 in order to improve productivity.

Developing artificial mixed diets for larval culture of sea cucumber, Holthuria leucospilota, and their effects on the internal microbiota

During the seedlings culture of sea cucumbers including Holthuria leucospilota, natural microalgae are generally used as ideal food for the pelagic larvae of sea cucumbers, which lead to a strong demand for microalgae production. However, microalgae production is time-consuming and laborious and susceptible to pests and variable whether, and unstable supply of microalgae often results in culture failure of sea cucumber larvae. In this study, we tested the effect of three different diets on the growth, survival rate, and internal microbiota composition of sea cucumbers aiming to develop an artificial diet for H. leucospilota larvae. The results showed that the sea cucumber larvae fed with the mixed artificial diet (composed of Sargassum powder, chilled macroalgae solution, wall-breaking Chlorella powder, and yeast powder) had the most balanced growth rate, highest survival rate, and a higher α-diversity and abundance of Plesiocystis, Haloferula, and Firmicutes in body when they were compared to the larvae fed with the natural bait, Chaetoceros muelleri. However, the abundance of potential pathogenic bacteria, Francisella and Acinetobacter, was higher in the larvae fed with the natural bait. In conclusion, the mixed artificial diet was developed for H. leucospilota larval culture, which can be used as a good alternative to live microalga with cumbersome processes.