Skeletonema Costatum Research Articles

Ecological Insights from Phytoplankton Diversity Off Veraval, Gujarat Coast, India

Phytoplankton species are sensitive to environmental and seasonal variability. This property of phytoplankton can be used to predict and study fluctuations in the ecological health of the system. In this study, phytoplankton diversity and its direct interactions with abiotic components of the ecosystem were studied to evaluate the health and stability of the coastal waters of Veraval, Gujarat coast, India. Results showed that diatoms dominated the ecosystem with a strong seasonal pattern of community succession. Waters were well churned and turbidity hindered penetration of light into deeper layers during the fall and winter monsoon season whereas stratification during spring inter-monsoon governed the distribution of different phytoplankton groups in the water column. These seasonal shifts resulted in a sincere pattern of annually re-occurring seasonal succession and formation of bloom events in the region. Apart from general phytoplankton diversity and its seasonal succession, the study intended to understand the forces governing the diversity and ecological system as a whole. To meet this objective, percent light intensities of chlorophyll-a, at various depths and temperatures were studied in relation to phytoplankton density. The correlation did not stand well for stations having active bloom formation showing that chlorophyll-a cannot be used as a proxy of phytoplankton biomass during bloom conditions. Thus excluding the points corresponding to active bloom conditions, second order polynomial equations were developed explaining the changes in chlorophyll-a concentration with variations in phytoplankton cell counts for study seasons. It was observed that most phytoplankton cells preferred upper well-lit layers of the water column with 100% light intensity followed by depths with 50% and 1% light intensities respectively. Study on temporal dynamics of the phytoplankton community in relation to temperature showed that the winter monsoon was characterized by a temperature range of 21.9 °C to 29 °C where Navicula distans was the most abundant phytoplankton species. Skeletonema costatum was the most abundant species at 27.2 °C during fall intermonsoon. Spring inter monsoon had an abundance of Navicula distans at both 28.35 °C and 28.9 °C.

Responses of Marine Diatom–Dinoflagellate Interspecific Competition to Different Phosphorus Sources

Phosphorus (P) is an essential nutrient element of phytoplankton, as well as a limiting factor for phytoplankton growth. It controls the succession of blooms from diatoms to dinoflagellates, especially in the East China Sea (ECS), where the eutrophication is serious. Most studies have only considered a single aspect of dissolved inorganic phosphorus (DIP) or dissolved organic phosphorus (DOP). In contrast, we investigated the growth interactions among the major bloom-forming marine diatom Skeletonema costatum and dinoflagellates Prorocentrum donghaiense and Karenia mikimotoi by using bi-algal cultures combined with DIP and DOP. Our results revealed that (1) P. donghaiense and K. mikimotoi have survival strategies that are superior to those of S. costatum in a bi-algal culture, whether under P-sufficient or P-deficient conditions, and (2) P. donghaiense has a slight competitive advantage over K. mikimotoi when P is sufficient, but the reverse is true when P is deficient. The difference in interspecific competition results at different P concentrations with DIP and DOP mainly arises from the variation in the utilization abilities of different species as regards different P sources, a finding which can also provide strong evidence for revealing the succession of diatoms and dinoflagellates blooms in the ECS.

Evaluation of different types of phytoplankton on rearing of vannamei shrimp larva (Litopenaues vanamei)

This study aims to determine the effect of giving different types of phytoplankton on the survival, abundance of bacteria, and water quality of white shrimp (Litopenaeus vannamei). This research was carried out from October to November 2020 at the Laboratory of the Brackish Water Cultivation Center (BBAP) Ujung Batee, Aceh Besar. The larvae of the tested shrimp used were shrimp at Nauplius stages 5-6. The method used was a Completely Randomized Factorial Design (CRD) with 5 treatments and 4 replications. Provision of phytoplankton Thalassiosira sp and artificial feed (treatment A), Chaetoceros sp and artificial feed (treatment B), Skeletonema costatum (Treatment C), a combination of phytoplankton Thallasiosira sp, Chaetoceros sp, Skeletonema costatum and artificial feed (treatment D) and artificial feed alone (treatment E). The test larvae were placed in a container with a density of seed stocking for each container was 100 fish/liter with a maintenance period of up to Post larval stage 1 (PL 1). The frequency of giving phytoplankton was done 2 times a day, namely at 09.00 am and 15.00 pm. While the frequency of artificial feed was 6 times, namely at 07.00 WIB in the morning, 11.00 WIB, 16.00 WIB in the afternoon, 21.00 WIB at night, 01.00 WIB in the morning, and 04.00 WIB in the morning. The results obtained showed that the treatment with phytoplankton had a significant effect on the survival of vanname shrimp larvae. Therefore, it can be concluded that the highest survival rate is in treatment D.Keywords: phytoplankton; survival; vaname; water quality

Evaluation of different types of phytoplankton on rearing of vannamei shrimp larva (Litopenaues vanamei)

This study aims to determine the effect of giving different types of phytoplankton to the survival, abundance of bacteria and water quality of white shrimp (Litopenaeus vannamei). This research was carried out from October to November 2020 at the Laboratory of the Brackish Water Cultivation Center (BBAP) Ujung Batee, Aceh Besar. The larvae of the tested shrimp used were shrimp at Nauplius stage 5-6. The method used was a Completely Randomized Factorial Design (CRD) with 5 treatments and 4 replications. Provision of phytoplankton Thalassiosira sp and artificial feed (treatment A), Chaetoceros sp and artificial feed (treatment B), Skeletonema costatum (Treatment C), a combination of phytoplankton Thallasiosira sp, Chaetoceros sp, Skeletonema costatum and artificial feed (treatment D) and artificial feed alone (treatment E). The test larvae were placed in a container with a density of seed stocking for each container was 100 fish/liter with a maintenance period of up to Post larval stage 1 (PL 1). The frequency of giving phytoplankton was done 2 times a day, namely at 09.00 am and 15.00 pm. While the frequency of artificial feed was 6 times, namely at 07.00 WIB in the morning, 11.00 WIB, 16.00 WIB in the afternoon, 21.00 WIB at night, 01.00 WIB in the morning and 04.00 WIB in the morning. The results obtained showed that the treatment with phytoplankton had a significant effect on the survival of vaname shrimp larvae. Therefore, it can be concluded that the highest survival rate is in treatment D.Keywords: phytoplankton; survival; vaname; water quality

Đa dạng sinh học thực vật phù du ở vùng hạ lưu sông Vàm Cỏ, tỉnh Long An

The study was conducted at ten sites in the lower of Vam Co river, Long An province from January to July 2018. The samples were collected by phytoplankton net and fixed with 5% formalin at the field. A total of 223 phytoplankton species were recorded, belonging to 106 genera, 66 families, 37 orders, and 6 divisions, of which the diatom group dominated in the species number. The average cell density ranged from 27 144 ± 8 508 cells/liter to 153 743 ± 45 300 cells/liter. The dominant species recorded in the study area include Merismopedia punctata, Oscillatoria acuta, Oscillatoria perornata, Oscillatoria sp., Microcystis aeruginosa, Microcystis panniformis, Lyngbya martensiana, Cyclotella meneghiniana, Skeletonema costatum, Coscinodiscus jonesianus, Melosira granulata. The high densities of phytoplankton were rich food sources for larvae, zooplankton, shrimp, fish, and bivalves. The Shannon - Weiner index, Simpson index, and Margalef index showed that the phytoplankton of lower Long An was diverse and abundant.

Algicidal characteristics of novel algicidal compounds, cyclic lipopeptide surfactins from Bacillus tequilensis strain D8, in eliminating Heterosigma akashiwo blooms.

Heterosigma akashiwo blooms have caused severe damage to marine ecosystems, the aquaculture industry and human health worldwide. In this study, Bacillus tequilensis D8 isolated from an H. akashiwo bloom area was found to exert high algicidal activity via extracellular metabolite production. This activity remained stable after exposure to different temperatures and light intensities. Scanning electron microscopy observation and fluorescein diacetate staining indicated that the algicidal substances rapidly destroyed algal plasma membranes and decreased esterase activity. Significant decreases in the maximum photochemical quantum yield and relative electron transfer rate were observed, which indicated photosynthetic membrane destruction. Subsequently, the algicidal compounds were separated and purified by high-performance liquid chromatography and identified as three surfactin homologues by interpreting high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy data. Among these, surfactin-C13 and surfactin-C14 exhibited strong algicidal activity against three HAB-causing species, namely, H. akashiwo, Skeletonema costatum, and Prorocentrum donghaiense, with 24 h-LC50 values of 1.2-5.31 μg/ml. Surfactin-C15 showed strong algicidal activity against S. costatum and weak algicidal activity against H. akashiwo but little activity against P. donghaiense. The present study illuminates the algicidal characteristics and mechanisms of action of surfactins on H. akashiwo and their potential applicability in controlling harmful algal blooms.

Potential risk from and prevention of phytoplankton outbreaks in blocking the cooling water system in a nuclear power plant on the Southeast China coast

The invasion or aggregation of marine biota in coastal waters has become a common problem, threatening the safety of cooling water systems in the context of environmental and climate changes. However, studies on issues of coastal nuclear power plants from the view of marine ecology have mostly focused on the thermal effluent, entrainment effect on organisms, residual chlorine, radioactivity, etc. There is a lack of information on the safety of cooling water systems in nuclear power plants blocked by marine biota. Based on field and historical datasets, this study screened phytoplankton species that may potentially block the cooling water system of the Fuqing nuclear power plant on the Southeast China coast, identified the phytoplankton risk and a risk calendar, and established a catalog of risk phytoplankton species for the cooling water system. The screening criteria were simultaneously required as follows: (1) particle size of cells or group >2000 μm; (2) phytoplankton bloom or aggregation events occurred in surrounding areas; (3) and species abundance maintained at >0.5×105 cells/L in the surrounding area. Nine high-risk species were screened out that can easily form colonies, clusters, and groups, including Thalassiosira diporocyclus, Thalassiosira subtilis, Noctiluca scintillans, Phaeocystis globosa, Pseudo-nitzschia pungens, Pseudo-nitzschia delicatissima, Skeletonema costatum, Skeletonema dohrnii, Paralia sulcata. Due to small cells or the formation of short chains, some dominant phytoplankton species, even those with advantages in abundance and occurrence, had difficulty threatening the reliability of cooling water systems in nuclear power plants. The outbreak of different phytoplankton species varied daily, and the risk of blockage was highest from April to July. The biological characteristics, ecological mechanisms underlying outbreaks of high-risk phytoplankton species are reviewed and discussed, suggesting a high degree of temporal and spatial variability of blockage risk. Finally, main prevention and control measures used against high-risk phytoplankton species are provided to imply new ideas and methods for nuclear power plants. These strategies have very important practical and scientific significance.

Toxicity Testing Organisms for Marine Ecotoxicological Research in China

Since the late 1970s, marine ecotoxicology began to sprout and develop in China. Based on the principles of dose-response relationships, some marine organisms are used in toxicity tests to evaluate the impact of marine pollutants on marine organisms and marine ecosystems. At the early stage, marine ecotoxicological research mainly focused on the bioaccumulation, biomagnification, and biodegradation of traditional pollutants such as heavy metals, radioactive elements, organotin, petroleum hydrocarbons, and pesticides, as well as their toxic effects on survival, growth, and other physiological indicators. With the development of Chinese industry, marine pollution has become increasingly serious. In addition to the traditional marine pollutants, toxicological research has been conducted on emerging pollutants with potential risks to marine ecosystems, such as POPs, emerging organic pollutants, nanomaterials, and microplastics. Moreover, the species of marine organisms used in toxicity testing have become more diverse. The selection of testing organisms is essential for evaluating toxicity correctly. The toxicity tests should be conducted on a variety of organisms from different trophic levels to ensure the comprehensive understanding of the impact of pollutants on marine ecosystems. The major types of marine organisms used in the toxicity testing include marine alga, protozoa, rotifera, annelida, mollusc, echinoderma, arthropoda, cephalopoda, and marine fish, which have been used in the toxicological studies of various marine pollutants. The outcome results can serve as the scientific basis for the ecological risk assessment of marine pollutants and the establishment of seawater quality criteria. It should be noted that the sensitivity of different testing organisms to different types of pollutants is quite diverse. Therefore, in addition to conducting a battery of tests on a variety of species which play important roles in marine ecosystems, elucidating the toxic mechanisms in different species is also important for marine ecotoxicological studies. The application of the above-mentioned organisms in marine ecotoxicology research in recent years is briefly reviewed here. Particularly, the six commonly used marine model species (Skeletonema costatum, Euplotes vannus, oysters, sea urchins, Tigriopus japonicus, and Oryzias melastigma) used in toxicity testing are introduced in detail.

Early warning of red tides using bacterial and eukaryotic communities in nearshore waters

Anthropogenic discharge activities have increased nutrient pollution in coastal areas, leading to algal blooms and microbial community changes. Particularly, microbial communities could easily be affected with variation in nutrient pollution, and thus offered a promising strategy to predict early red tides warning via microbial community-levels variation and their keystone taxa hysteretic responses to nutrient pollution. Herein high-throughput sequencing technology from 52 samples were used to explore the variation of microbial communities and find the significant tipping points with aggravating nutrient conditions in Xiaoping Island coastal area. Results indicated that bacterial and microeukaryote communities were generally spatial and seasonal heterogeneity and were influenced by the different nutrient conditions. Procrustes test results showed that the comprehensive index of organics polluting (OPI), total nitrogen (TN), inorganic nitrogen (DIN), and total phosphorus (TP) were significantly correlated with the composition of bacteria and microeukaryotes. A SEGMENTED analysis revealed that the threshold of TN, DIN, and NH4–N for bacterial community were 0.23 ± 0.091 mg/L, 0.21 ± 0.084 mg/L, 0.09 ± 0.057 mg/L, respectively. Tipping points for TN, DIN, and NH4–N agreed with the concentration during Ceratium tripos and Skeletonema costatum blooms. Co-occurrence network results found that Planktomarina, Acinetobacter, and Verrucomicrobiaceae were keystone and OPI-discriminatory taxa. The abundant changes of Planktomarina at station A1 were significantly correlated with the development of C. tripos blooms (r = 0.55, p < 0.05), and also significantly correlated with TN, DIN, and NO3–N (r≥|0.55|, p < 0.05). The abundant changes of Acinetobacter and Verrucomicrobiaceae at station C1 were significantly correlated with the development of C. tripos blooms (r ≥ 0.77, p < 0.05), and also significantly correlated with PO4–P (r ≥ 0.64, p < 0.05). The dynamic abundance of keystone taxa showed that the trend of rapid changes could be monitored 1.5 months before the occurrence of red tide. Therefore, this study provides an assessment method for early warning of red tide occurrence and factors that trigger red tide.

The Addition of Seaweed Extract (Sargassum sp) as Fertilizer on Culture Media on The Total Density of Skeletonema costatum Cells

Microalgae Skeletonema costatum is a natural food that contains nutrients needed for aquaculture. Seaweed contains several nutrients and has body regulatory substances, namely auxin, gibberellin and cytokinin which are useful for increasing the growth of microalgae cells, including S. costatum. The study aims to examine the addition of Sargassum sp. on culture media on cell density of S. costatum. The benefit of this study is to obtain scientific information regarding the addition of Sargassum sp., thus, it can be a natural fertilizer that can be used in the economical cultivation of S. costatum. This study consisted of 5 treatments, namely the concentration of Sargassum sp. extract in media (control) 0 mg/500 mL, 25 mg/500 mL, 50 mg/500 mL, 75 mg/500 mL and a concentration of 100 mg/500 mL, these treatments were repeated three times. S. costatum cell density was checked every 6 hours. The results showed that the use of extracts of Sargassum sp. 100 mg/500 mL had the highest cell density of S. costatum (2.08×107 cells/mL), followed by 75 mg/500 mL (2.00×107 cells/mL), 50 mg/500 mL (1.99×107 cells/mL, 25 mg/500 mL (1.97×107 cells/mL), and 0 mg/500 mL (1.05×107 cells/mL).

Biomineral Flocculation of Kaolinite and Microalgae: Laboratory Experiments and Stochastic Modeling

AbstractIn estuaries and coastal waters, the flocculation of cohesive sediments is significantly affected by extracellular polymeric substances secreted by microalgae. In this study, laboratory experiments are carried out to explore the role of two typical microalgae (Skeletonema costatum and Cyclotella meneghiniana) on suspended fine‐grained sediments under various turbulent shear and environmental conditions. The results show that the shear rate is a dominant factor in controlling the biomineral flocculation processes, and the existence of microalgae generally enhances the aggregation of mineral sediments with microalgae. It is also found that floc size distributions (FSDs) and mean sizes are clearly influenced by different algal species and concentrations, especially under intensive turbulent environments. Moreover, a quasi‐Monte Carlo (QMC) based bivariate population balance model is developed to simulate the FSDs of sediment‐algae flocs. This model is reasonably validated by two analytical solutions and laboratory observations, and indicates a potential extension for tracking the properties of microalgae‐associated fine sediment flocs due to the discrete nature of the QMC method.

Effects of phosphate on the toxicity and bioaccumulation of arsenate in marine diatom Skeletonema costatum

The effects of nutrient phosphate (P) at environmentally relevant levels on the toxicity of arsenic (As) in marine microalgae have been rarely known. In the present study, we explored the toxicity and bioaccumulation of As in a globally distributed diatom species Skeletonema costatum at different ambient P concentrations. The results showed that As toxicity was suppressed at elevated P concentrations. Intracellular As content ([As]intra) and the molar ratio of intracellular As to P ([As:P]) were negatively correlated with the ambient P concentrations. The trends of As bioaccumulation were substantially different between the relatively low (0, 0.5 and 1.5 μM) and high P concentrations (7.5 and 37.5 μM). Both [As]intra and [As:P] suggested that As bioaccumulation was a better factor to explain the As toxicity comparing to the ambient As concentration. The 4 h As uptake kinetics at different P concentrations followed Michaelis–Menten kinetic pattern. The maximum uptake rates (Vmax) decreased with the increase in P concentrations, and the half-saturation constants (Kd) remained constant except for that at extremely high P concentration (37.5 μM-P), suggesting the depression of P on As uptake was mainly due to the non-competitive effect. Overall, these results demonstrate that the P concentration in seawater is an important factor affecting As toxicity and bioaccumulation in the marine diatom. This study therefore helps us better understand the effects of eutrophication on the toxicity and biogeochemistry of As in the marine environment.

Features of Temperature Adaptation of Phaeodactylum tricornutum, Nitzschia sp., and Skeletonema costatum (Bacillariophyceae) under Different Light Conditions.

Two types of possible adaptive response of the photosynthetic apparatus of diatoms to the changes in growth temperature conditions are shown. The first type is a temperature-dependent change in the content of chlorophyll in the cell, aimed at matching the rates of light and dark reactions of photosynthesis (noted in Phaeodactylum tricornutum and Nitzschia sp. 3). At the limiting light intensity, a temperature decrease from 20 to 5°C leads to an increase in the initial slope of light dependence of the C/Chl ratio; under the optimal light conditions at a temperature decrease from 20 to 10°C and from 10 to 5°C, the C/Chl ratio increases 1.5-fold in both species. The second type of response to the changes in growth temperature conditions was observed in Skeletonema costatum, for which the chlorophyll content in the cell does not depend on the temperature in the range of 10-20°C. The adaptation of the photosynthetic apparatus in this case probably occurs due to the changes in the activity of enzyme systems and in the rate of enzyme processes. The potential productivity of all studied species of algae at 10°C, calculated as the increase in biomass per unit of chlorophyll per day, does not differ significantly. Under the conditions of light inhibition, a temperature decrease leads to a progressive decrease in the content of chlorophyll in the cells of all algal species under study due to a decrease in the rate of pigment synthesis against the background of its intense photooxidation.

Equilibrium and Kinetic Modeling of Crystal Violet Dye Adsorption by a Marine Diatom, Skeletonema costatum.

Significant efforts have been made to improve adsorbents capable of eliminating pollutants from aqueous solutions, making it simple and quick to separate from the treated solution. In the current study, the removal of Crystal Violet Dye (CVD) from an aqueous synthetic solution onto a marine diatom alga, Skeletonema costatum, was investigated. Different experiments were conducted as a function of different pH, contact time, adsorbent dosage, temperature, and initial CVD concentration. The highest adsorption efficiency (98%) was obtained at 0.4 g of S. costatum, pH 3, and a contact time of 120 min, at 25 °C. Furthermore, Fourier-transform infrared spectroscopy (FTIR) results display that binding of CVD on S. costatum may occur by electrostatic and complexation reactions. Moreover, the Brunauer–Emmett–Teller surface area analysis (BET) obtained was 87.17 m2 g−1, which, in addition to a scanning electron microscope (SEM), reveals large pores that could enhance the uptake of large molecules. However, the equilibrium adsorption models were conducted by Halsey, Langmuir, Freundlich, Henderson, and Tempkin isotherm. In addition, multilayer adsorption isotherm best described the uptake of CVD onto S. costatum. The maximum monolayer adsorption capacity (qmax) was 6.410 mg g−1. Moreover, thermodynamic parameters of the adsorption studies suggested that the uptake of CVD onto S. costatum was endothermic and spontaneous. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic equations were applied to model the adsorption kinetic data. It was seen that the kinetics of the adsorption may be described using pseudo-second-order kinetic equations. Finally, the present work concluded that the marine diatom alga S. costatum is suitable as a natural material for the adsorption of CVD.

Biological indicators as tools for monitoring water quality of a hot spot area on the Egyptian Mediterranean Coast

El-Mex Bay is a semi-sheltered coastal embayment located west of Alexandria, the Egyptian Mediterranean Sea. It is considered as a hot spot area receiving industrial, agricultural, and domestic wastes from the adjacent Lake Mariut through El-Umum Drain. To evaluate the water quality of the bay, phytoplankton and macroalgae as biological tools were investigated seasonally concerning physicochemical parameters from 2018 to 2019. The results indicated that the Bay harbored a diversified phytoplankton community (162 species), comprising 99 freshwater forms, 38 marine, 22 euryhaline, and only 3 brackish forms. The total average phytoplankton abundance was 419,414 unit/L. Few species were responsible for the main bulk of phytoplankton namely Merismopedia tenuissima, Cylindrotheca closterium, Cyclotella sp., Skeletonema costatum, Scenedesmus quadricauda, Scenedesmus bijugus, and Tetradesmus dimorphus. During the study period, El-Mex Bay was affected by the presence of 13 harmful and /or toxic algal species, among which the mediophyte species Skeletonema costatum was responsible for the peak occurring during autumn (2018). The results of the recorded nutrients indicated that the Bay is highly loaded, where NH4, NO2, NO3, PO4, and SiO4 attained 141.68 µM, 25.61 µM, 151.16 µM, 10.73 µM, and 232.86 µM, respectively. The macroalgal flora was represented only by the two opportunistic species (Ulva fasciata and Ulva intestinalis). Both species could survive in freshwater conditions exhibiting very broad salinity tolerance (6.51–38.41‰) and a high level of nitrogenous compounds. Those results revealed that El-Mex Bay suffers from pollution and deterioration of water quality.

Individual and combined toxicity of microplastics and diuron differs between freshwater and marine diatoms

Microplastics are considered as the emerging pollutants, which not only directly affect aquatic organisms, but also causes combined pollution by adsorbing other pollutants. Diuron, as one of the most widely used herbicides, is frequently monitored in the aquatic environment for its adverse effects on aquatic organisms. However, little is known about the combined toxicity of microplastics and diuron to aquatic organisms, especially diatoms. In this study, freshwater diatom (Cyclotella meneghiniana) and marine diatom (Skeletonema costatum) were selected to study the individual and combined toxicity of microplastics (polystyrene, 0.6– 1.0 μm) and diuron. Experimental concentrations of microplastics and diuron were set at 50 mg/L and 100 μg/L, respectively, which have been shown to significantly inhibit the growth of aquatic organisms. Results suggested that both single microplastics and single diuron significantly inhibited the growth of the two diatoms, while significant SOD and MDA increase were only found in single diuron exposure. For diatoms exposed to individual microplastics, the microplastic particles adsorbed inside Cyclotella sp. and those aggregated around Skeletonema sp. were the major factor inhibiting the growth of diatom, respectively. According to the independent action model, the combined toxicity for both diatoms were all antagonistic. The adsorption behavior of microplastics to diuron alleviated the intracellular damage to diatoms caused by diuron, and the oxidative stress induced by diuron mitigated the physical damage to diatoms caused by microplastics. Collectively, our findings suggest that the co-existence of microplastics and diuron may affect their respective toxicity to diatoms. The mechanism of this “cross-phenomenon” between microplastics and diuron and their combined toxicity to different aquatic organisms need to be further studied.

Inorganic Nitrogen Uptake Characteristics of Three Typical Bloom-Forming Algae in the East China Sea

Inorganic nitrogen (N) is an important element for eutrophication and harmful algal bloom (HAB) formation. However, the roles of inorganic N in HAB outbreaks are still unclear. Here, we compared the affinities and abilities for inorganic N uptake and assimilation among three typical bloom-forming algae in the East China Sea (ECS), Skeletonema costatum, Prorocentrum donghaiense and Alexandrium pacificum by investigating the uptake and enzymatic (nitrate reductase (NR) and glutamine synthetase (GS) kinetics for nitrate and ammonia. The Ks of nitrate and ammonium in S. costatum was lower than those in P. donghaiense and A. pacificum. The NR activity of S. costatum and P. donghaiense exhibited a positive relationship with the nitrate concentration, and NR activity of S. costatum was nearly 4-fold higher than that of P. donghaiense at high nitrate concentration. However, the NR activity of A. pacificum could not be detected. The GS activity of three species decreased with the increase of ammonium concentrations, and the highest GS activity was detected in A. pacificum. S. costatum presented the highest affinity for nitrate and ammonium, followed by P. donghaiense and A. pacificum. Moreover, P. donghaiense exhibited the highest affinity for intracellular ammonium. Our results characterized the differences in inorganic nitrogen uptake among the three typical bloom-forming algae, which may contribute to the formation of blooms in the coastal waters of the ECS.

Characterization and classification of estuarine suspended particles based on their inorganic/organic matter composition

An 11 hours survey was performed on the 17th of September 2014 in the Rhine Region Of Freshwater Influence (Rhine-ROFI) about 10 km downstream of the mouth of the Rotterdam Waterway during calm weather conditions. Suspended Particle Matter (SPM) measurements were performed during a full tidal cycle, near the seabed, at neap tide, and samples were taken at 0.6 meter above bed for on-board analysis. The measurements were performed with (a) LISST 100X, a submersible particle size analyzer, (b) LISST-HOLO, a submersible digital holographic camera, (c) a home-made underwater camera and (d) an on-board LabSFLOC2 video microscopy equipment that used in-situ collected samples. The first aim of the present study was to compare the results obtained from the different monitoring techniques and to characterize the different types of suspended particles found in-situ. It was found that that the highly anisotropic particles present in the water column lead to multiple peaks in the Particle Size Distributions (PSD) found using the LISST 100X. Using the LISST-HOLO, underwater camera and LabSFLOC2 camera these particles could properly be imaged and meaningful PSD’s were obtained using these techniques in the size range &amp;gt; 20 μm. LabSFLOC2, LISST-HOLO and the underwater camera moreover provide information on the size and aspect ratio of particles. On the other hand, LISST 100X can be used to detect the fine fraction (&amp;lt;20 μm), a size range that is not accessible for the other techniques. From the analysis of the data on the survey day, three classes of particles were identified, based on composition rather than size (the sizes given here are purely indicative): (1) mineral (inorganic) sediment particles in the range size 5 - 20 μm, (2) organic/inorganic aggregates in the size range 20 - 200 μm and (3) organic particles in the size range &amp;gt; 200 μm. A large range of settling velocities (0.1 - 10 mm/s) and aspect ratios between 1 and 10 were recorded by video microscopy (LabSFLOC2). This spreading in settling velocities and aspect ratio was due to the different properties (shape, effective density and size) of the particles in the water column. The second aim of the study was to reproduce the flocs found in-situ in the lab and investigate the kinetics of flocculation between inorganic and living organic matter. Laboratory experiments were conducted with grab samples obtained from Port of Rotterdam harbour and living microalgae (Skeletonema costatum). The results of these experiments showed a shift in effective density upon addition of living algae to the sediment, which confirmed the flocculation ability between sediment and microalgae. The flocculation occured on a timescale of minutes and lead to flocs having a large spread in density for a given size, due to the heteregeous inorganic/organic composition of the flocs. This spread in density was at the origin of the large range of settling velocities for a given floc size observed in-situ, which leads to conclude that organic matter should be an important input parameter in sediment transport models.

Characterization of Fine-Scale Turbulence Generated in a Laboratory Orbital Shaker and Its Influence on Skeletonema costatum

Turbulence is one of the ubiquitous aspects of aquatic systems and affects many physical and biological processes. Based on direct velocity measurements and a computational fluid dynamics (CFD) simulation, we characterized the distribution of the turbulent kinetic dissipations rates (ε) in an orbital shaker system within a range of rotation frequencies. CFD was able to estimate the ε distribution in containers accurately, which was confirmed by other two methods and was independent of velocity measurement. The results showed that ε was linearly correlated with the rotational frequencies. Despite the existence of gradients of ε and the fact that a mean circular horizontal flow was formed within the tank, the energy levels of the whole tank varied spatially within an order of magnitude and the ε distributions at different rotational frequencies were similar, suggesting that the ε distribution in the whole tank could be seen as quasi-homogeneous. To investigate the influence of turbulence on algae growth, culture experiments of a typical diatom—Skeletonema costatum were carried out under different turbulence conditions. Our results suggested turbulence mixing promoted nutrient uptake and growth of Skeletonema costatum, which could be attributed to the break of the diffusion-limited resource concentration boundary layer surrounding phytoplankton.

Testing cocolitophoro Emiliania huxleyi on an aquaculture‐produced purple sea urchin ( Paracentrotus lividus ) larvae diet

The nutritional quality of Paracentrotus lividus larvae's feed plays an important role in their survival and development. The lipid profile of microalgae is largely reflected in the successful development of different metamorphoses. Emiliania huxleyi is the most common cocolitophoro in the oceans and the most important microalgae for calcium carbonate sedimentation on the ocean floor. Despite its biological and geological importance, the application of this microalgae in sea urchin larvae feeding is still unknown. In this work, the performance of E. huxley was evaluated as a P. lividus larvae feeding. Three diets were tested: D1: (Rhodomonas marina), D2 (R. marina, Skeletonema costatum, Emiliania huxleyi) and D3 (E. huxley). Larvae fed with the D2 diet (75.8%) and D3 (74.9%) had a survival at 15 DAH higher than D1 (48.7%). Larvae development was significantly higher in larvae fed with more than one species of algae (D1 and D2), compared with larvae fed only with E. huxley. On day 15 DAH, the number of larvae in the pre-fixation state was much higher in D1 and D2. The analysis of the E. huxley fatty acid profile has a relatively low content of total fatty acids, being, however, rich in DHA (22: 6ω3). The DHA/EPA ratio in these microalgae is significantly higher than the other microalgae used in this work. This research also found that a multiple microalgae species diet promotes optimal development, with the E. huxley species contributing to a high survival rate.