Trophic Organisms Research Articles

Acute Exposure to Polyethylene Microbeads and Effects on the Water Flea Moina Macrocopa.

Microplastics merit attention as they can be ingested by lower trophic organisms, transferred to the food web, and pose potential risks to higher trophic levels. This study investigated the accumulation and effects of polyethylene microbeads (PEMBs, 63-75μm) on adult water flea Moina macrocopa (600-800μm), an order-magnitude difference in size, as a result of acute exposure. The organisms were exposed to PEMBs in four treatments of 0 (the Control), 5, 50, and 500mg PEMB/L for examining PEMB accumulation, survival and reproduction of the organisms after the 24- and 48-h exposures. In general, M. macrocopa ingested PEMBs within 24-h exposure and reached the cumulative PEMB accumulation value of 0.17 ± 0.21 beads/adult after 48-h exposure in the 500mg PEMB/L treatment. Exposure to PEMBs resulted in a statistically significant decrease of the cumulative survival rates, from 93 ± 12% in the Control to 37 ± 21% in the 500mg/L treatment. Nevertheless, exposure to PEMBs did not significantly reduce the cumulative reproduction (p > 0.05), although a decrease was observed. This study suggests that the relatively large-size PEMBs could be ingested by the relatively small-size M. macrocopa and pose potential risks to these organisms.

Potato yield and quality are linked to cover crop and soil microbiome, respectively

Crop-specific cultivation practices including crop rotation, cover cropping, and fertilisation are key measures for sustainable farming, for which soil microorganisms are important components. This study aims at identifying links between agronomic practices, potato yield and quality as well as soil microorganisms. We analysed the roles of cover crops and of the soil prokaryotic, fungal, and protistan communities in a long-term trial, differing in crop rotation, i.e. winter wheat or silage maize as pre-crop, presence and positioning of oil radish within the rotation, and fertilisation, i.e. mineral fertiliser, straw, manure, or slurry. Up to 16% higher yields were observed when oil radish grew directly before potatoes. Losses of potato quality due to infection with Rhizoctonia solani-induced diseases and common scab was 43–63% lower when wheat + oil radish was pre-crop under manure or straw + slurry fertilisation than for maize as pre-crop. This contrast was also reflected by 42% higher fungal abundance and differences in β-diversity of prokaryotes, fungi, and protists. Those amplicon sequence variants, which were found in the treatments with highest potato qualities and differed in their abundances from other treatments, belonged to Firmicutes (2.4% of the sequences) and Mortierellaceae (28%), which both comprise potential antagonists of phytopathogens. Among protists, Lobosa, especially Copromyxa, was 62% more abundant in the high potato quality plots compared to all others, suggesting that specific higher trophic organisms can improve crop performance. Our findings suggest that successful potato cultivation is related (1) to planting of oil radish before potatoes for increasing yield and (2) to fertilisation with manure or straw + slurry for enriching the microbiome with crop-beneficial taxa.

Freshwater algal biofilm assemblages are more effective than invertebrate assemblages at aggregating microplastics

Microplastics, plastic particles less than 5 mm in length, are a ubiquitous pollutant in the environment, but research on freshwater microplastic contamination is lacking. A possible fate of microplastics in freshwater environments is to become entangled or aggregated in biofilms, which are matrices of algae, bacteria, and micro invertebrates that grow on underwater surfaces, following a progression of settling algae, periphyton, and finally invertebrate colonization. This in-situ study at the Oasis Marina at National Harbor in Oxon Hill, Maryland, examined how the taxonomic assemblages of freshwater biofilms in the Potomac River are associated with the number of microplastics aggregated within them. Aluminum discs, acting as artificial substrate for biofilm growth, were deployed at the water's surface and at 2 m depth to survey biofilm assemblage and were sampled monthly from October 2021–October 2022. Microplastic abundances in the water column were measured every 2 weeks over the same period. Spatial and temporal trends in trapped and suspended microplastics, water quality parameters (temperature, dissolved oxygen, pH, salinity, conductivity, turbidity, ammonia, nitrate, and phosphate), and biofilm assemblages were measured and compared to explore factors affecting the abundance of microplastics and their partitioning between the water column and biofilms. Water quality had no measurable impact on microplastic abundance in the water column at either depth, but temperature was negatively correlated to microplastic abundance in biofilms. As the weather warmed and biofilms progressed to invertebrate settling, they tended to contain fewer microplastics. This may have occurred because less biologically rich biofilms, primarily composed of unicellular algal colonies, provide a favorable surface for microplastic deposition. Understanding seasonal changes in biofilm assemblage and microplastic abundance may help track the fate of microplastics in freshwater systems, particularly in their interactions with lower trophic organisms.

Effects of Silver, Gold, and Platinum Nanoparticles on Selected Nematode Trophic Groups

Abstract As trophic organisms, nematodes play an essential role in the soil environment: they mineralize nutrients into plant-available forms, are a food source for other soil organisms, and feed on pathogenic organisms and plant pests, therefore regulating populations of soil microorganisms. The plant-parasitic nematodes are important pests of crops. Nanoparticles (NP) are increasingly used in agriculture and other production sectors. They are present in the soil, not necessarily in trace amounts, and can affect various soil organisms, including nematodes. In this article, the effects of silver (Ag), gold (Au), and platinum (Pt) nanoparticles on the mortality and reproduction activity of selected nematode species from two trophic groups: entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and Steinernema feltiae) and plant parasitic nematodes (PPN) (Xiphinema diversicaudatum, Ditylenchus dipsaci, Heterodera schachtii) were studied under laboratory conditions. All nanoparticles decreased the nematode population to an extent depending on the nematode species, nanoparticle type, and exposure time. AgNP had the greatest nematicidal effect, except for AuNP, which reduced the population of H. schachtii the most. The greatest sensitivity to AgNP was observed in X. diversicaudatum (100% mortality), D. dipsaci (90% mortality), and 37 to 13% mortality in other species. Effect of AuNP and PtNP on entomopathogenic nematodes was comparable to the control, not treated with nanoparticles. AuNP and PtNP similarly influenced nematode mortality. However, the effect of nanoparticles on new generations of entomopathogenic nematodes developing in host larvae Galleria mellonella was inconclusive. All nanoparticles decreased the number of larvae of S. feltiae and increased the number of H. bacteriophora migrating outside the cadavers compared to the control.

Microplastic contamination in the sediment of the Johor Strait Estuary, Malaysia

The issue of microplastics has garnered significant attention in light of their potential environmental hazards and possible health effects on higher trophic organisms and humans. However, the available information is restricted and knowledge about the interaction between microplastics in aquatic sediments and the microplastic-related impacts of aquaculture activities, and this area has not yet been adequately researched. This research looks at the occurrence and properties of microplastics in the bed sediment from Perna veridis aquaculture activity areas, in the Strait of Johor, Malaysia. Bed sediments were collected in replicates from five sampling sites using a box corer (Wildco). The extracted organic matter was digested with 30% hydrogen peroxide (H2O2) before being separated using NaCl and ZnCl solutions. The inspection of plastic debris was conducted via a Stereomicroscope (HSZ-600) at magnifications ranging from 40x to 45x and considered according to morphology, size, and colour. Microplastic polymers were validated using Attenuated Total Reflection Fourier Transferred Infra-Red (ATR-FTIR) spectroscopy. The sediment samples exhibited a varying range of microplastic abundance, with values ranging from 29 to 60 particles/kg.d.w. Microplastics within the size range of 101-500μm (63%) predominated in all samples collected, with fragments (79%) and fibres (18%) being the main morphologies of MPs found. The dominant particles found in the sediment were polypropylene (PP) and polyamide. The findings suggest that aquaculture practises may have an impact on the presence of microplastics (MPs) in bottom sediment, as these locations are well-known aquaculture areas for Perna veridis.

Comparison of the Composition and Abundance of Phytoplankton Based on Different Land Use in the Cisadane River, Tangerang Regency

Phytoplankton is an autotrophic organism that produce its own food through the process of photosynthesis with the help of sunlight which forms the basis of water productivity to be utilized for trophic organisms above. In freshwater, river plankton are categorized as potamoplankton. Rivers are a dominant freshwater ecosystem and have a more stable morphology than other freshwaters. Changes in land function is triggered by an increase in human population, an increase in the number of residential areas and industrial activities that discharge untreated waste into the river. Because of the importance of phytoplankton for life, it is necessary to conduct research on the Comparison of Phytoplankton Composition and Abundance Based on Different Land Uses in the Cisadane River, Tangerang Regency. In this study, sampling was carried out using a purposive sampling method by measuring parameters such as pH, temperature, and water transparency. Identification of phytoplankton composition and abundance was carried out using the Sedgwick Rafter Counting Cell (SRCC) using the sweep method. The results of this study obtained 23 phytoplankton genera from 6 classes consisting of: Bacillaryophyceae, Cyanophyceae, Chlorophyceae, Conjugatophyceae, Trebouxiophyceae, and Zygnematophyceae. Phytoplankton abundance was 185-490 Ind/L with the highest abundance in both areas are Bacillaryopiceae and Navicula. The diversity index was 1.307-2.124 and the dominance index was 0.201-0.461. Water quality parameters that affect the composition and abundance of phytoplankton are water-transparency, pH, and water temperature. The fertility level of the Cisadane River waters has an oligotrophic fertility level.

Contrasting currents drive geographic variability in the biomass of Pacific saury (Cololabis saira), zooplankton, and phytoplankton in the northwestern Pacific

Exploring the biomass relationships among fish, zooplankton, and phytoplankton and the potential mechanisms that drive changes in their biomass are important for us to understand the structure and dynamics of aquatic ecosystems. In this study, we thus measured the biomass of planktivorous Pacific saury (Cololabis saira), zooplankton, and phytoplankton in the less-explored northwestern Pacific to illustrate their biomass relationships, and to explore underlying mechanisms driving the spatial patterns of biomass for these trophic organisms. Our results showed that the sampling area could be divided into the Kuroshio-driven low-nutrient and high-chlorophyll region (i.e, LNHC) and the Oyashio-driven high-nutrient and low-chlorophyll region (i.e, HNLC). In the LNHC, the phytoplankton biomass was on average threefold higher than that in the HNLC. By contrast, the biomass of zooplankton in the LNHC was averagely twofold lower than that in the HNLC. Differently, the average stock of Pacific saury in the LNHC was generally consistent with that in the HNLC. Apart from the positive correlation between zooplankton biomass and the stocks of Pacific saury, there were no linear relationships of biomass across the three organisms. The implication is that the top-down effects by zooplankton grazing or Pacific saury feeding are unlikely to cascade further down to the phytoplankton biomass in the northwestern Pacific. Based on the canonical correspondence analysis, we found that the biomass of Pacific saury, zooplankton, and phytoplankton between HNLC and LNHC responded differently to specific environmental factors (e.g., temperature, salinity, and nutrients), indicating that the contrasting Oyashio and Kuroshio currents had an impact on the geographic variation of the biomass for these organisms. Altogether, our findings provide insights into the biomass relationships among Pacific saury, zooplankton, and phytoplankton, and the researches for the dynamics of these trophic organisms in marine ecosystems.

Drivers of diatom production and the legacy of eutrophication in two river plume regions of the northern Gulf of Mexico

In the northern Gulf of Mexico (nGoM), the Louisiana Shelf (LS) and Mississippi Bight (MB) subregions are influenced by eutrophication to varying degrees. Despite recognition that dissolved silicon may regulate diatom productivity in the nGoM, there is only one published data set reporting biogenic silica (bSiO2) production rates for each subregion. We report that bSiO2 production rates on the LS and MB are high and appear to be controlled by different nutrients among seasons. Despite exceptional upper trophic level biomass regionally, which suggests significant primary production by diatoms (as in other systems), gross euphotic-zone integrated bSiO2 production rates are lower than major bSiO2 producing regions (e.g. upwelling systems). However, when normalizing to the depth of the euphotic zone, the bSiO2 production rates on the LS are like normalized rates in upwelling systems. We suggest local river-plume influenced hydrography concentrates diatom productivity within shallow euphotic zones, making production more accessible to higher trophic organisms. Comparison of rates between the LS and MB suggest that the fluvial nitrate within the LS stimulates bSiO2 production above that in the MB, which has a smaller watershed and is less eutrophic (relatively). Beyond understanding the factors controlling regional bSiO2 production, these data offer the most comprehensive Si-cycle baseline to date as the LS and MB will likely exchange freely in the mid to late century due to land subsidence of the Mississippi River delta and/or sea-level rise.

Study of Phytoplankton Biomass and Environmental Drivers in and around the Ross Sea Marine Protected Area

The Southern Ocean plays a vital role in the global climate system and the life cycle of high-latitude marine life. Phytoplankton is an important source of primary productivity in this ecosystem. Its future changes could affect Southern Ocean geochemistry, carbon export, and higher trophic organisms. To better protect Antarctica, three different marine protected areas (MPA) have been established in the Ross Sea region. Because time-continuous and regionally complete data are difficult to obtain in this region, we obtained data from ocean model outputs to understand the spatiotemporal variability of phytoplankton biomass in this region. This study explored the correlation between phytoplankton biomass and key environmental factors. Phytoplankton biomass peaks in February as temperatures rise and sea ice melts. Correlations also vary between different protected areas. The correlation between biomass, nitrate, and salinity in the Krill Research Zone (KRZ) area was significantly different from other protected areas. In addition, in the context of global warming, Antarctica lacks temperature perception. The model results show a downward trend in temperature and an increase in sea ice coverage in the western Ross Sea that other studies have also pointed to. How phytoplankton biomass will change in protected areas in the future is a question worth considering. Finally, the study simply simulates future regional trends by comparing the biomass distribution in hot years to average years. This will increase our knowledge of the polar system.

Impact of Pacific Ocean heatwaves on phytoplankton community composition

Since 2013, marine heatwaves have become recurrent throughout the equatorial and northeastern Pacific Ocean and are expected to increase in intensity relative to historic norms. Among the ecological ramifications associated with these high temperature anomalies are increased mortality of higher trophic organisms such as marine mammals and seabirds, which are likely triggered by changes in the composition of phytoplankton, the base of the marine trophic food web. Here, we assimilated satellite ocean color data into an ocean biogeochemical model to describe changes in the abundance of phytoplankton functional types (PFTs) during the last decade’s (2010s) warm anomalies in the equatorial and northeastern Pacific Ocean. We find important changes associated with the “Blob” warm anomaly in the Gulf of Alaska, where reduced silica supply led to a switch in community composition from diatoms to dinoflagellates, resulting in an increase in surface ocean chlorophyll during the Summer–Fall of 2014. A more dramatic change was observed in the equatorial Pacific, where the extreme warm conditions of the 2016 El Niño resulted in a major decline of about 40% in surface chlorophyll, which was associated with a nearly total collapse in diatoms.

Mesoscale eddies modulate the dynamics of human fishing activities in the global midlatitude ocean

AbstractFrequent fishing activities are causing overfishing, destroying the habitat of marine life, and threatening global marine biodiversity. Understanding the dynamics of fishing activities and their drivers is crucial for designing and implementing effective ocean management. The fishing activities in the open sea are reported to be characterized by high spatial variability in local waters; however, it is still unclear whether their high spatial variability is random or regulated by oceanographic variations. Mesoscale eddies are ubiquitous swirling currents that dominate locally biogeochemical processes. Previous case studies presented an ongoing debate regarding how eddies exert impacts on high trophic organisms, which imposes limitations on understanding the dynamics of fishing activities based on the bottom‐top control hypothesis from eddies to fish and fishing activities. By combining global fishing activities from deep learning and oceanic eddy atlases from satellite monitoring, we showed that the spatial variations in fishing activities were closely related to mesoscale eddies in the global midlatitude ocean, confirming that fishing activities primarily targeting tuna, were aggregated in (repelled from) anticyclonic (cyclonic) eddy cores. This eddy‐fishing activity relationship was opposite to satellite‐observed primary production but corresponded well with the temperature and oxygen content in deeper water. By integrating existing evidence, we attribute eddy‐related fishing activities to a reasonable hypothesis that warm and oxygen‐rich deeper water in anticyclonic eddies relieves the thermal and anoxic constraints for diving predation by tuna while the constraints are aggravated in cold and oxygen‐poor cyclonic eddies.

Metal(Loid)s in Aquatic Products and Their Potential Health Risk

Aquatic products decrease environmental burdens and improve human health by supplying various essential nutrients, while their contamination with metal(loid)s could pose health risks to humans through food chain. In this study, the concentrations, trophic magnification and health risks of multiple metal(loid)s in various aquatic products were analyzed, including arsenic, cadmium, mercury, lead, cobalt, manganese, iron, copper, nickel and zinc. The results showed that the total concentrations of the metal(loid)s in marine foods from the same sea area were in the following order: seaweeds > shellfish > cephalopods > crustaceans > saltwater fish > freshwater fish. Arsenic speciation analysis indicated that high concentrations of arsenolipids were detected in lower trophic organisms. The maximum level of organoarsenic in seafood should be evaluated because of the potential toxicity of arsenolipids and arsenosugar metabolites. Weekly intake of metal(loid)s was far below the recommended provisional tolerable weekly intake even with excessive consumption of aquatic products. The hazard index was above 1 for excessive consumers, while our results also indicated that the health risks from aquatic products could be sharply decreased by reducing the ingestion of seaweeds and cephalopods. The study provided valuable guidance on the consumption of aquatic products by the general public.Graphical abstract

Triphenylmethane dye (C52H54N4O12) is potentially a hazardous substance in edible freshwater fish at trace level: toxicity, hematology, biochemistry, antioxidants, and molecular docking evaluation study.

Malachite green (C52H54N4O12) is a synthetic dye that is used in textile industries as a colorant and in aquaculture sectors to contain microbial damage. Aquatic contamination of malachite green(MG) has been reported globally. Fish is the highest trophic organism among aquatic inhabitants, highly sensitive to waterborne contaminants (metals, coloring agents, etc.). Toxicity of waterborne chemicals on nontarget organisms can be determined by assessing biomarkers. Assessing blood parameters and tissue antioxidants (enzymatic and nonenzymatic) is useful to evaluate MG toxicity. To initiate the MG toxicity data for freshwater fish (Cyprinus carpio), the median lethal toxicity was primarily evaluated. Then, hematological, blood biochemical (glucose, protein, and cholesterol) and tissue biochemical (amino acids, lipids), and vital tissue (gills, liver, and kidney) antioxidant capacity (CAT, LPO, GST, GR, POxy, vitamin C, and GSH) of C. carpio were analyzed under acute (LC50-96h) and sublethal (Treatment I-1/10th and Treatment II-1/5th LC50-96h) exposure periods (28days). Molecular docking for MG with hemoglobin was also obtained. Biomarkers examined were affected in the MG-treated groups with respect to the control group. Significant changes (p < 0.05) were observed in hematology (Hb, RBCs, and WBCs), glucose, proteins, lipids and tissue CAT, LPO, and GST activities under acute MG exposure. In sublethal treatment groups, biomarkers studied were significant (p < 0.05) throughout the study period. The potential for MG binding to hemoglobin was tested in this study. MG is potentially a multiorgan toxicant. Literally a chemical that is harmful to the aquatic environment if safety is concerned.

Fish and Prey Resources in Reservoir Coves with and without Offshore Artificial Habitat Structures

Artificial habitat structures are used to mitigate habitat loss within aquatic ecosystems and to increase angler catch rates; however, the potential trophic outcomes of concentrating fish at structure additions are rarely evaluated. We compared fish and fish prey assemblages between reservoir coves with and without newly added offshore habitat structures (PVC cubes enclosing 2.25 m3). Further, we tested whether offshore habitat additions changed fish assemblage and abundance in littoral habitats of treated coves. Coves with offshore structures had higher concentrations of fish and an assemblage structure dominated by Pomoxis and Lepomis species at offshore sites compared to coves without offshore structures. There was no evidence for an effect of offshore structures on fish relative abundance and assemblage structure in nearby littoral habitats. Zooplankton and benthic macroinvertebrate abundances did not change because of the addition of habitat structures. Lack of a response of lower trophic organisms may be due to low predation mortality or else losses to predation are replaced by increased prey production or immigration at the offshore structures. Our results indicated that artificial structures effectively concentrated fish, but increases in fish density may be partitioned among newly available structure in offshore habitats and existing structure within littoral habitats. Future studies are needed to test for a relationship between foraging space and food resources provided by artificial habitats, which may be useful for optimizing the number, size, and material composition of structures used in habitat enhancement programs.

Effects of environmental factor fulvic acid on AgNPs food chain delivery and bioavailability

Due to its antimicrobial activity, silver nanoparticles (AgNPs) have become the most commonly applied nanomaterials. However, the potential ecotoxicological toxicity of AgNPs in the environment is still unclear. Here we assessed the trophic transfer and toxicity of commercially manufactured polyvinyl pyrrolidone (PVP)-coated AgNPs using a model food chain from Escherichia coli (E. coli) to Caenorhabditis elegans (C. elegans). Our results demonstrated that AgNPs could be accumulated in E. coli and transferred to C. elegans that preyed on the bacteria. Although low concentration of AgNPs had no significant inhibition on E. coli, they could affect germ cell apoptosis, reproduction ability and population size of C. elegans through food chain. Importantly, natural organic matter (NOM), which is omnipresent in environmental system, could increase the accumulation of AgNPs in E. coli and C. elegans, and significantly enhance the ecotoxicity of AgNPs. Our findings indicated that potential risks of nanomaterial through food chain should be considered for higher trophic organisms. And environmental factors could play an important role in transport of nanomaterials and altering their accumulation and toxicity in ecosystem.

Effect of selenium nanoparticles induced toxicity on the marine diatom Chaetoceros gracilis

Discharge of nanomaterials into the environment contributes to a diverse group of pollutants. In the present study, the toxicity of selenium nanoparticles (SeNPs) on the marine diatom Chaetoceros gracilis was studied in the laboratory by conducting 96 h toxicity experiments. The SeNPs were synthesized by reducing sodium selenite using L-cysteine and characterized by spectroscopic and microscopic techniques. X-ray photoelectron spectroscopic (XPS) data showed a distinctive selenide peak at 56 eV, indicating the oxidation states Se3d3/2 and Se3d5/2. Raman spectra results indicated the characteristic A1 and S mode of selenium (Se). Growth inhibitory experiments were performed (LC50 14.63 mg/L) for 96 h using various concentrations of SeNPs and its membrane damage to cells was observed. Upon treatment with SeNPs, an increased percentage of reactive oxygen species (ROS) production was detected from 28.77±3.13% to 130.55±3.16% after 96 h. Malonaldehyde (MDA), a biomarker of lipid peroxidation was quantified and exposure to 50 mg/L of SeNPs significantly (p < 0.05) increased MDA concentration from 4.31±0.02 to 5.05±0.05 µM in 96 h. The morphological distortion, including cell wall damage, that affects the cellular integrity upon exposure to SeNPs was evident from microscopic studies. These results clearly indicate that, even at lower concentrations, SeNPs toxicity on lower trophic organisms is significant enough to cause cellular level alterations.

Scavenging of select radionuclides and trace elements by pelagic Sargassum in the Caribbean Sea

In recent years, the North Atlantic and the Caribbean Sea have experienced unusual and unprecedented pelagic Sargassum blooms, which may adversely affect coastal ecosystems and productive ocean. Sargassum has the potential to scavenge trace elements and radionuclides from seawater, and when bioaccumulated and thus concentrated, can pose a potential threat to higher trophic organisms, including humans that consume impacted seafood. In this study, trace elements and naturally-occurring U/Th-series radionuclides were measured in Sargassum that were collected in the coastal waters of the Caribbean Sea (Antigua/Barbuda, Belize, and Barbados) to better define baseline concentrations and activities, and to assess the scavenging potential for these trace elements and radionuclides. The mean concentration of trace elements observed in Sargassum collected across these three Caribbean Sea are ranked accordingly to the following descending order: Sr > As>Fe > Mn > Zn > Ni > V > C > Cd > Se > Co > Cr > Pb > Ag > Hg. 210-Po and 210Pb activities in Sargassum were observed to be more elevated than previously reported values.

The impact of engineered nanomaterials on the environment: Release mechanism, toxicity, transformation, and remediation

The presence and longevity of nanomaterials in the ecosystem, as well as their properties, account for environmental toxicity. When nanomaterials in terrestrial and aquatic systems are exposed to the prevailing environmental conditions, they undergo various transformations such as dissociation, dissolution, and aggregation, which affects the food chain. The toxicity of nanomaterials is influenced by a variety of factors, including environmental factors and its physico-chemical characteristics. Bioaccumulation, biotransformation, and biomagnification are the mechanisms that have been identified for determining the fate of nanomaterials. The route taken by nanomaterials to reach living cells provides us with information about their toxicity profile. This review discusses the recent advances in the transport, transformation, and fate of nanomaterials after they are released into the environment. The review also discusses how nanoparticles affect lower trophic organisms through direct contact, the impact of nanoparticles on higher trophic organisms, and the possible options for remediation.

Vertical Distribution of Phytoplankton Community and Pigment Production in the Yellow Sea and the East China Sea during the Late Summer Season

Phytoplankton community structure, which plays an important role in determining productivity and food web structure, can provide important information for understanding variations in marine ecosystems under projected climate change scenarios. Rising temperatures due to climate change will increase and intensify water stratification. To understand the community composition and distribution characteristics of phytoplankton under stratified conditions, phytoplankton pigments were analyzed in the Yellow Sea (YS) and East China Sea (ECS) during the late summer season. In addition, pigment production was measured to estimate the physiological characteristics of phytoplankton relating to light, which is an essential element of photosynthesis. During our observation period, no distinct differences were found in the community composition and pigment production of phytoplankton in the YS and the ECS, but differences in the vertical distribution were observed. Overall, the dominant phytoplankton classes at the surface depth were pico-sized cyanobacteria (46.1%), whereas micro- and nano-sized diatoms (42.9%) were the abundant most classes at a 1% light depth. The major factors controlling the vertical distributions of the phytoplankton community were temperature and nutrients (i.e., nitrate and ammonium). Cyanobacteria were positively correlated with water temperature and ammonium, whereas diatoms were negatively related to water temperature and positively correlated with nitrates. Based on the pigment production, it was found that cyanobacteria at the surface layer encountered excessive irradiance conditions during the study period. The productivity of the cyanobacterial community could be decreased under high-light and high-temperature conditions. This means that cyanobacteria could have a negative influence on the quantity and quality of food available to upper trophic organisms under warmer conditions.

Methylmercury in caddisflies and mayflies: Influences of water and sediment chemistry

Quantifying methylmercury (MeHg) concentrations and uptake at the base of the food web is useful for assessing mercury exposure risk to higher trophic level organisms. Higher MeHg concentrations near the base of the food web may result in more MeHg exposure and accumulation in higher trophic organisms. Here, we analyze MeHg in caddisflies, mayflies, lake water, and sediment collected from two temperate lakes and one brook in Kejimkujik National Park, Nova Scotia, Canada. Overall, caddisfly larvae MeHg (15.38–276.96 ng/g; n = 29) was not significantly correlated with water chemistry. Whereas mayfly naiads MeHg (14.28–166.82 ng/g; n = 31) was positively correlated with water MeHg (rs = 0.43), negatively correlated with pH (rs = −0.49), and positively correlated with dissolved organic carbon (DOC; rs = 0.48). Of the mercury in insect tissues, the %MeHg ranged from 56 to 75 % in caddisfly larvae and 38–47 % in mayfly naiads. MeHg bioaccumulation factors (BAF) varied greatly (water to tissue BAFs = 0.145 × 106–1.054 × 106; sediment to tissue BAFs = 0.017 × 106–0.541 × 106). This study highlights the importance of quantifying variations in MeHg bioaccumulation and BAFs of common aquatic insect bioindicators at the base of complex food webs.