Phytoplankton Organisms Research Articles

Calcareous Nannofossil variability controlled by Milankovitch and sub-Milankovitch periodicity in the Monte San Nicola section (Gelasian GSSP / MIS 100–104)

The Quaternary marks the beginning of the ice ages, with the establishment of a stable Northern Hemisphere ice sheet. The Monte San Nicola section, southern Sicily (Italy) is the Global Boundary Stratotype Section and Point of the Gelasian Stage of the Lower Quaternary Subseries and is attracting new attention for providing valuable information on paleoclimate evolution.Here we present a paleoenvironmental reconstruction based on new data from calcareous nannoplankton, the phytoplankton organisms that are sensitive to sea surface changes and water column dynamics. We adopt statistical and signal analysis to support our paleoenvironmental model. The most evident paleoenvironmental signal throughout the investigated interval is the contrast between the abundance patterns of placoliths and Florisphaera profunda, the former pointing to surface productivity (water column mixing, shallow nutricline), the latter to the establishment of a deep nutricline. The observed nutricline depth shift occurred with a regular precessional pace, following Northern Hemisphere summer insolation and, likely, North African monsoon activity. A significant periodicity of 8 kyr, in tune with late Quaternary Heinrich events, is also observed in nannoplankton taxa, supporting previous findings on the existence of suborbital climatic variability even at the Pliocene-Pleistocene transition.

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.

Delta-5 elongase knockout reduces docosahexaenoic acid and lipid synthesis and increases heat sensitivity in a diatom.

Recent global marine lipidomic analysis reveals a strong relationship between ocean temperature and phytoplanktonic abundance of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are essential for human nutrition and primarily sourced from phytoplankton in marine food webs. In phytoplanktonic organisms, EPA may play a major role in regulating the phase transition temperature of membranes, while the function of DHA remains unexplored. In the oleaginous diatom Phaeodactylum tricornutum, DHA is distributed mainly on extraplastidial phospholipids, which is very different from the EPA enriched in thylakoid lipids. Here, CRISPR/Cas9-mediated knockout of delta-5 elongase (ptELO5a), which encodes a delta-5 elongase (ELO5) catalyzing the elongation of EPA to synthesize DHA, led to a substantial interruption of DHA synthesis in P. tricornutum. The ptELO5a mutants showed some alterations in transcriptome and glycerolipidomes, including membrane lipids and triacylglycerols under normal temperature (22°C), and were more sensitive to elevated temperature (28°C) than wild type. We conclude that PtELO5a-mediated synthesis of small amounts of DHA has indispensable functions in regulating membrane lipids, indirectly contributing to storage lipid accumulation, and maintaining thermomorphogenesis in P. tricornutum. This study also highlights the significance of DHA synthesis and lipid composition for environmental adaptation of P. tricornutum.

Biometric analysis of food products of hybrid hypoophthalmichthys (Hypophthalmichthys spp.) to determine their nutritional value and use in the food industry

This scientific work describes research, the purpose of which was to study the spectrum of nutrition and the composition of the food lump, as studies aimed at assessing specific weight (%) of essential nutrients (glycogen, proteins, and lipids) in particular organs and tissues of different size and mass groups of the hybrid of Silver carp and Bighead carp in ponds and reservoirs in different periods of the year. In 2018, and 2019, the juveniles of the hybrid of Silver carp and Bighead carp in ponds and reservoirs mainly consumed phytoplankton organisms (from 30 to 90% by mass), among which green, diatom, and euglena algae predominated by mass in the food group. Zooplankton occupied an insignificant place in fish nutrition (up to 5%), even though its quantity and biomass were sufficient in reservoirs. The hybrid of Silver carp and Bighead carp does not hurt zooplankton communities, so it can be included in the stocking volume of Silver carp. The feeding spectrum and rations of different groups of Silver carp and Bighead carp in ponds and reservoirs had a well-defined seasonal character related to the composition of feed objects. In all size and mass groups of the hybrid of silver and bighead carp from ponds and reservoirs in 2018, and 2019, mostly satisfactory values of general metabolism indicators were found – glycogen, proteins, and lipids in the liver, gills, and muscles of fish. The difference found in the availability of essential nutrients in the body of the studied fish indicates a change in the intensity and direction of their metabolic processes.

Cross-domain diversity effects: linking diatom species richness, intraspecific richness, and biomass production to host-associated bacterial diversity.

Interactions between bacteria and microalgae are important for the functioning of aquatic ecosystems, yet interactions based on the biodiversity of these two taxonomic domains have been scarcely studied. Specifically, it is unclear whether a positive biodiversity-productivity relationship in phytoplankton is largely facilitated by niche partitioning among the phytoplankton organisms themselves or whether associated bacterial communities play an additional role in modifying these diversity effects. Moreover, the effects of intraspecific diversity in phytoplankton communities on bacterial community diversity have not been tested. To address these points, we factorially manipulated both species and intraspecific richness of three diatoms to test the effects of diatom species/strain diversity on biomass production and bacterial diversity in algae-bacteria communities. The results show that diatom intraspecific diversity has significant positive effects on culture biomass and the diversity of the associated free-living bacterial community (0.2-3μm size fraction), which are comparable in magnitude to species diversity effects. However, there were little to no effects of diatom diversity on host-associated bacterial diversity (>3μm size fraction), or of bacterial diversity on biomass production. These results suggest a decoupling of bacterial diversity from the diatom diversity-productivity relationship and provide early insights regarding the relations between diversity across domains in aquatic ecosystems.

Long-term adjustment of phytoplankton structure to environmental traits at timescales during lifetime development and over generations

Long-term ecological research of deep Lake Mondsee covers over more than six decades of phytoplankton observation. According to our study, phytoplankton groups of various phenological traits are suitable to address the impact of two major environmental stressors: nutrient surplus by eutrophication from 1968 to 1998 and warming by climate change. Here, we focus on phytoplankton biovolume, phytoplankton assemblage structure, net changes rates, and phytoplankton biodiversity. Biweekly net change-dependent persistence of phytoplankton assemblages followed a dome-shaped relationship of observations. A short-term persistence of taxonomic traits along weeks is predominant and contributes to the structural stabilization of phytoplankton assemblages. This short-term persistence is interpreted by the benefit of lifetime adjustment of phytoplankton organisms. The long-term development phytoplankton structure is discussed as an alignment of organisms over generations. Single key taxa, as Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis &Komárek 1988, which are omnipotent players in phytoplankton assemblages and occur during different environmental scenarios in the long-term, are most suitable for long-term ecological research. Our findings interpret that phytoplankton taxa are excellent organisms to track the impact of environmental constraints due to their short generation time (1), their lifetime adjustment (2), and the re-occurrence in the long-term over generations (3).

Surface light modulation by sea ice and phytoplankton survival in a convective flow model

Plankton dynamics depend in a complex manner on a variety of physical phenomena, according to both experimental and numerical data. In particular, experimental field studies have highlighted the relation between phytoplankton survival and turbulent upwelling and downwelling from thermal convection. Recent numerical works have also shown the importance of accounting for advective transport by persistent structures in simulation models. In nutrient-rich polar marine environments phytoplankton blooms are critically limited by light availability under ice-covered waters. Such heterogeneity of the light intensity distribution, in association with a large-scale coherent fluid flow, can give rise to nontrivial growth dynamics. In this work we extend a previous advection-reaction-diffusion model of phytoplankton light-limited vertical dynamics in the presence of convective transport. Specifically, we consider horizontally heterogeneous light conditions through the use of two regions with different production regimes, modelling the absence (presence) of light under (in between) obstacles. Such a model is intended as an idealized representation of nonuniformly ice-covered polar waters. By means of numerical simulations, we find that the main role of advective transport is to hinder phytoplankton growth, but also that such effect depends on the positions of the obstacles with respect to the upwelling and downwelling flow regions. Furthermore, we show that the sinking speed due to the density difference between phytoplankton organisms and water, while small, plays an important role, which depends on how it adds to the flow. These results indicate that advective transport can have a crucial impact on the survival conditions of sinking phytoplankton species in polar environments.

DEVELOPMENT OF A METHODOLOGY FOR MODELING THE STATE OF THE WATER ECOSYSTEM BASED ON THE METHODS OF ECOLOGICAL STOICHIOMETRY, TAKING INTO ACCOUNT THE ENERGY APPROACH

The article develops a methodology for modeling the state of the food chain of the aquatic ecosystem in terms of biomass growth of producers based on ecological energy stoichiometry. The research is based on a number of sinusoidal functions developed during the simulation of the monthly solar energy arrival per unit area by latitude. The average forecast indicator of energy input for southern Ukraine of 2518 MJ/m2 is very close to the results of similar applied measurements in Odesa. For modeling, the average latitude for Ukraine is 48°23′, the average inclinations of the sun for each of the 8 months according to the astronomical calendar (about 14), as well as the average duration of a sunny day, and the angle of incidence and reflection of the sun’s rays on water are determined based on them, taking into account only the angle of incidence at noon, and changes during the day (the angle of reflection ranges from 17.5 in June to 29.26 in September). Correction coefficients for latitude were derived, the percentage ratio of days with cyclonic weather, due to which there is an increase in reflection due to cloudiness and waves, was calculated – 638 hours and 30 minutes. The efficiency of photosynthesis for the main groups of phytoplankton organisms was calculated, which is 1.98 % for Chlorophyta, 2.38 % for Cyanophyta, 1.96 % for Euglenophyta and 1.65 % for all others. The overall average efficiency of photosynthesis was thus 1.83 %. Taking into account the area of ​​the water mirror, the arrival of energy, reflection, scattering and absorption. Taking into account the efficiency of photosynthesis, a stoichiometric simulation of the increase in biomass of producers was carried out. The potential of carbon dioxide deposition is 2.6 kg/m2 per year, oxygen release is 1.92 kg/m2, and biomass growth is 1.8 kg/m2. This is the maximum potential. The study is supplemented by derived correction factors based on energy and toxicological indices of environmental safety, ORP and the Redfield ratio. This gives a real total energy per square meter of 12335.66473 kJ, biomass growth of 773.1266184 g/m2. The predictive model yields 577.6 kg/ha per year of fish, which is close to the value of natural bioproductivity for herbivorous fish (505 kg/ha). At the stage of food chain analysis, it is proposed to additionally use the deduced regularity of the effect of salinity on the growth of macroliths and correction coefficients of fish productivity for different soils. The basis for automation and local modeling is laid.

Content of Nitrate, Phosphate, and Chlorophyll-a in Terkul Water, Rupat Strait, Riau

The waters of Terkul are related to the strait of Rupat. Around the Terkul area, there is an oil and gas industry with transportation, storage, processing, and distribution of oil supplies to various regions in Sumatra through ship transportation. This activity causes the waters of the Rupat Strait to be prone to oil pollution. Oil pollution can reduce the quality of the waters and cause nutrient content in the waters to decrease. Nutrients greatly affect the concentration of chlorophyll-a in the waters. Chlorophyll-a is a pigment capable of photosynthesis and is present throughout phytoplankton organisms. The purpose of this study was to analyze the association of nitrate concentration and phosphate concentration to chlorophyll-a. the study was conducted in April 2021. Waters sample was collected from the waters of Terkul and sample analysis was conducted in the Marine Chemistry Laboratory. The results of the study show that the association between chlorophyll-a and phosphate corresponds to the regression result of obtaining a value (r) of 0.67. Linearly shows a strong relationship

Changes in Toxin Production, Morphology and Viability of Gymnodinium catenatum Associated with Allelopathy of Chattonella marina var. marina and Gymnodinium impudicum.

Allelopathy between phytoplankton organisms is promoted by substances released into the marine environment that limit the presence of the dominating species. We evaluated the allelopathic effects and response of cell-free media of Chattonella marina var. marina and Gymnodinium impudicum in the toxic dinoflagellate Gymnodinium catenatum. Additionally, single- and four-cell chains of G. catenatum isolated from media with allelochemicals were cultured to evaluate the effects of post exposure on growth and cell viability. Cell diagnosis showed growth limitation and an increase in cell volume, which reduced mobility and led to cell lysis. When G. catenatum was exposed to cell-free media of C. marina and G. impudicum, temporary cysts and an increased concentration of paralytic shellfish toxins were observed. After exposure to allelochemicals, the toxin profile of G. catenatum cells in the allelopathy experiments was composed of gonyautoxins 2/3 (GTX2/3), decarcarbamoyl (dcSTX, dcGTX2/3), and the sulfocarbamoyl toxins (B1 and C1/2). A difference in toxicity (pg STXeq cell−1) was observed between G. catenatum cells in the control and those exposed to the filtrates of C. marina var. marina and G. impudicum. Single cells of G. catenatum had a lower growth rate, whereas chain-forming cells had a higher growth rate. We suggest that a low number of G. catenatum cells can survive the allelopathic effect. We hypothesize that the survival strategy of G. catenatum is migration through the chemical cloud, encystment, and increased toxicity.

ABUNDANCE OF PHYTOPLANKTON AS A DETERMINANT OF WATER QUALITY IN THE COASTAL AREA OF DUMAI BARAT DISTRICT, DUMAI CITY, RIAU PROVINCE

The coastal area in Dumai Barat District has experienced many changes in the function of coastal land and mangroves so that various human activities provide input of organic and inorganic materials that will affect air quality and phytoplankton. This research was conducted in March-April 2022. There are 3 stations with sampling 3 times, once/week. The air quality parameters measured were temperature, brightness, current velocity, dissolved oxygen, free carbon dioxide, pH, salinity, phosphate, nitrate, and phytoplankton. The results show that the temperature is 29.33-32.00oC, brightness is 58.67-69.67 cm, current velocity is 0.99-1.00 m/s, dissolved oxygen is 6.20-8.32 mg/L, free carbon dioxide is 7.92-15.84 mg/L, pH is 7.07-7.10, salinity is 20-28 ppt, phosphate is 0.7661-0.9955 mg/L, and nitrate is 0.6530 -0.8224 mg/L. There were 25 types of phytoplankton found, namely Bacillariophyceae (12 species), Chlorophyceae (6 species), Dinophyceae (1 species), Cyanophyceae (2 species), Euglenoidea (1 species), Coscinodiscophyceae (1 species), and Trebouxiophyceae (2 species ). The abundance of phytoplankton in the coastal area of West Dumai is 15,308-31,603 cells/L. Data analysis shows that the air quality is still good and can be tolerated by phytoplankton organisms with mesotrophic fertility.

Spatio-Temporal Distribution of Phytoplankton and Water Quality of Some Rivers of Haute Sanaga Department (Central Africa)

In Cameroon, rivers are subjected to physicochemical disturbances, which increase the degradation of water quality. The aim of this study was to determine the spatio-temporal diversity of the phytoplankton groups and to evaluate the environmental parameters of the sampling sites in order to assess the quality of water in two hydrographic networks. Physicochemicals analyzes were carried out according to the standard methods while phytoplankton organisms were harvested by direct sampling and analyzed by the Utermöhl method. The analysis of Ammonia Nitrogen, Dissolved Oxygen, Electric Conductivity, Nitrates, Orthophosphates, pH, Temperature, and Turbidity.of water revealed the poor state of health of the water. Data from the Long Dry Season differed significantly (p < 0.05) from those recorded in other seasons. The phytoplankton communities were made up of Chlorophyta, Chrysophyta, Cyanophyta, and Euglenophyta with 11 classes dominated by Bacilliarophyceae (12 210 Ind/mL) and Cyanophyceae (6 208 Ind/mL). Phytoplankton densities were higher the Long Rainy Season and much lower in the Small Dry Season than in the Long Dry Season. Station near NODISCAM indicated significant organic pollution under the effect of agro-industrial discharges operating upstream of this company. For this station, the different values showed significant differences (p < 0.05) from one station to another. Finally, spatio-seasonal variations of phytoplankton densities showed logical responses to changes of physicochemical conditions in the environment. This work highlights the need to treat wastewater from collection channels before its dump into the natural environment, to prevent progressive eutrophication of the receiving aquatic environment, and poisoning by water consumption.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance.

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

Pigment-based chemotaxonomy of the phytoplankton community from a marine mussel farming area

Microscopy technique is traditionally employed for assessing phytoplankton taxonomy. However, chemical approaches, such as the identification of biomarker pigments, allow to elucidate microalgae groups more quickly, in addition to detecting these valuable compounds. This study aimed to identify the pigment profile of microalgae species and to determine the seasonal pigment fluctuation in a marine mussel farm. Water samples were collected periodically between the years of 2014 and 2015. Phytoplanktonic organisms were isolated and cultivated in f/2 liquid medium under controlled temperature and light cycle. Cell content extracts from each unialgal culture and water sample were analyzed by High Performance Liquid Chromatography (HPLC). Pigment profiles of 13 marine microalgae strains were identified (12 Diatoms and 1 Dinoflagellate). Chlorophyll a and fucoxanthin were most present in Diatoms, while peridinin was the major carotenoid in Prorocentrum micans. Bacillariophyceae had higher density in the summer and fall. Dinophyceae, Cryptophyceae, Euglenophyceae, Prasinophyceae, Dictyophyceae and Ebriidea, had an increase in density during winter and spring. Following the trend of phytoplankton groups, pigments such as fucoxanthin, zeaxanthin, diadinoxanthin, chlorophyll c3 and c2, were identified throughout the year. Prasinoxanthin, peridinin, dinoxanthin and antheraxanthin were identified in samples collected during winter and spring.

Мониторинг концентраций хлорофилла в Баренцевом море: сравнение многолетних in situ и спутниковых данных

Phytoplankton organisms are the basis of the trophic chain and primary producers in the pelagial of the Barents Sea. The variation in phytoplankton biomass during the growing season is closely related to the change in chlorophyll a concentration. The data on the concentration of chlorophyll a in situ collected during the long-term (2006, 2007, 2010, 2013, 2015–2019) MMBI expedition research were compared with remote satellite sensing data. More than 200 in situ samples and satellite data were analyzed on the same dates in a 5x5 km square centered on the sampling point. It was revealed that permanent cloud cover over the Barents Sea interferes with the complete remote monitoring of this water area. The small number of coincidences of concentrations in situ with satellite data does not allow achieve global monitoring goals. Having analyzed the relationship of sea surface temperature as a key factor affecting the spatial and temporal distribution of chlorophyll a, a high degree of correlation (r = 0.89) between the parameters under consideration was determined, which indicates a sufficiently high reproducibility of the data of field measurements by satellite instruments.

Environmentally induced functional shifts in phytoplankton and their potential consequences for ecosystem functioning

Phytoplanktonic organisms are particularly sensitive to environmental change, and, as they represent a direct link between abiotic and biotic compartments within the marine food web, changes in the functional structure of phytoplankton communities can result in profound impacts on ecosystem functioning. Using a trait-based approach, we examined changes in the functional structure of the southern North Sea phytoplankton over the past five decades in relation to environmental conditions. We identified a shift in functional structure between 1998 and 2004 which coincides with a pronounced increase in diatom and decrease in dinoflagellate abundances, and we provide a mechanistic explanation for this taxonomic change. Early in the 2000s, the phytoplankton functional structure shifted from slow growing, autumn blooming, mixotrophic organisms, towards earlier blooming and faster-growing microalgae. Warming and decreasing dissolved phosphorus concentrations were linked to this rapid reorganization of the functional structure. We identified a potential link between this shift and dissolved nutrient concentrations, and we hypothesise that organisms blooming early and displaying high growth rates efficiently take up nutrients which then are no longer available to late bloomers. Moreover, we identified that the above-mentioned functional change may have bottom-up consequences, through a food quality-driven negative influence on copepod abundances. Overall, our study highlights that, by altering the phytoplankton functional composition, global and regional changes may have profound long-term impacts on coastal ecosystems, impacting both food-web structure and biogeochemical cycles.

Strong reorganization of multi-domain microbial networks associated with primary producers sedimentation from oxic to anoxic conditions in an hypersaline lake.

Understanding the role of microbial interactions in the functioning of natural systems is often impaired by the levels of complexity they encompass. In this study, we used the relative simplicity of an hypersaline crater lake hosting only microbial organisms (Dziani Dzaha) to provide a detailed analysis of the microbial networks including the three domains of life. We identified two main ecological zones, one euphotic and oxic zone in surface, where two phytoplanktonic organisms produce a very high biomass, and one aphotic and anoxic deeper zone, where this biomass slowly sinks and undergoes anaerobic degradation. We highlighted strong differences in the structure of microbial communities from the two zones and between the microbial consortia associated with the two primary producers. Primary producers sedimentation was associated with a major reorganization of the microbial network at several levels: global properties, modules composition, nodes and links characteristics. We evidenced the potential dependency of Woesearchaeota to the primary producers' exudates in the surface zone, and their disappearance in the deeper anoxic zone, along with the restructuration of the networks in the anoxic zone toward the decomposition of the organic matter. Altogether, we provided an in-depth analysis of microbial association network and highlighted putative changes in microbial interactions supporting the functioning of the two ecological zones in this unique ecosystem.

Detection of the maximum resistance to the herbicides diuron and glyphosate, and evaluation of its phenotypic cost, in freshwater phytoplankton.

One of the most important anthropogenic impacts on freshwater aquatic ecosystems close to intensive agriculture areas is the cumulative increase in herbicide concentrations. The threat is especially relevant for phytoplankton organisms because they have the same physiological targets as the plants for which herbicides have been designed. This led us to explore the evolutionary response of three phytoplanktonic species to increasing concentrations of two herbicides and its consequences in terms of growth and photosynthesis performance. Specifically, we used an experimental ratchet protocol to investigate the differential evolution and the limit of resistance of a cyanobacterium (Microcystis aeruginosa) and two chlorophyceans (Chlamydomonas reinhardtii and Dictyosphaerium chlorelloides) to two herbicides in worldwide use: glyphosate and diuron. Initially, the growth rate of M. aeruginosa and D. chlorelloides was completely inhibited when they were exposed to a dose of 0.23 ppm diuron or 40 ppm glyphosate, whereas a higher concentration of both herbicides (0.46 ppm diuron or 90 ppm glyphosate) was necessary to abolish C. reinhardtii growth. However, after running a ratchet protocol, the resistance of the three species to both herbicides increased by an adaptation process. M. aeruginosa and D. chlorelloides were able to grow at 1.84 ppm diuron and 80 ppm glyphosate and C. reinhardtii proliferated at twice these concentrations. Herbicide-resistant strains showed lower growth rates than their wild-type counterparts in the absence of herbicides, as well as changes on morphology and differences on photosynthetic pigment content. Besides, herbicide-resistant cells generally showed a lower photosynthetic performance than wild-type strains in the three species. These results indicate that the introduction of both herbicides in freshwater ecosystems could produce a diminution of primary production due to the selection of herbicide-resistant mutants, that would exhibit lower photosynthetic performance than wild-type populations.

Salinity, a climate-change factor affecting growth, domoic acid and isodomoic acid C content in the diatom Pseudo-nitzschia seriata (Bacillariophyceae)

ABSTRACT Freshening of the oceans is a predicted outcome of climate change. Marine phytoplankton organisms are in general affected by salinity changes and, given their key role in oceanic food webs and geochemical cycles, it is important to investigate the response of phytoplankton species to salinity changes. Diatom species of the genus Pseudo-nitzschia can form massive and, at times, toxic blooms, because several Pseudo-nitzschia species produce the neurotoxin domoic acid. Domoic acid can cause amnesic shellfish poisoning in humans and harm animals in the marine food web. The species Pseudo-nitzschia seriata can produce domoic acid in cold-water areas, like the Arctic. Hence, it is relevant to investigate the response of P. seriata to different salinity levels. Three strains of P. seriata were exposed to four different salinity levels (15, 20, 30 and 40). None of the strains grew at salinity 15, and maximum growth rates were found at salinity 30. All three strains contained toxins at salinities 20–40, with the highest cellular content occurring at salinity 20. The peak in toxin content was related to a significantly lower growth rate. However, the higher toxin content overrode the lower growth rate, ultimately resulting in a higher toxin potential at salinity 20. In addition to domoic acid, all strains contained isodomoic acid C in surprisingly high amounts, similar to the domoic acid content.

Effects of two synthetic pyrethroids on Arthrospira platensis Gomont growth and antioxidant parameters

The transport of pesticides from application areas to other areas results in pesticide contamination and this sort of contamination has led to unexpected environmental problems worldwide. It is important to determine the responses of phytoplanktonic organisms to these chemicals for an understanding of the effects of pesticides on aquatic ecosystems. In this study, Arthrospira platensis Gomont cyanobacteria were exposed to different concentrations of the pesticides cypermethrin (0-50 µg mL-1) and deltamethrin (0-2 µg mL-1). Changes in chlorophyll-a concentration, the absorbance of OD560, antioxidant parameters (SOD, APX, GR, MDA, H2O2, and proline) were determined under the pesticide exposure. Our results showed that there is a decrease in OD560 absorbance and chlorophyll-a content proportionate to the increase of pesticide levels. Superoxide dismutase enzyme activity decreased with Cyp and Dlm application in A. platensis cultures. Glutathione reductase enzyme activity also decreased with Cyp applications but did not change with Dlm application. Ascorbate peroxidase enzyme activity increased with Cyp treatments but did not change with Dlm applications. Although malondialdehyde and hydrogen peroxide contents did not change with Cyp applications, they increased with Dlm applications. Proline contents increased with Cyp applications but decreased with Dlm applications. In conclusion, deltamethrin is more toxic than cypermethrin in the concentrations applied.