Three molecular assays were used to detect and quantify white spot syndrome virus (WSSV) in DNA extracted from seston size-fractioned (0.02, 0.2, 1.2, and 20 μm) samples collected from a coastal ...lagoon and an adjacent shrimp farm. From 107 DNA extracts, only two from one sample tested positive for WSSV with nested PCR in the 1.2 and 20 μm fractions. These results were confirmed by a semi-quantitative (IQ2000TM WSSV Detection and Prevention System) and a quantitative (IQREALTM WSSV Quantitative System) detection system based, based, respectively, on nested PCR and real-time PCR. A first viral load reference value (6.54 × 104 WSSV copies/mL) was established in a seston size fraction (1.2−20 μm). The results suggest that WSSV could be associated with both resuspension of fine clays and silts, and nanoplankton and organic colloids during infectious events.
Eutrophication has been shown to increase production of nutritionally low‐quality cyanobacteria and decrease the long‐chain polyunsaturated fatty acid (PUFA) content of seston. Contrarily, lake ...browning inhibits cyanobacteria contribution in seston and favours poorly grazable mixotrophic algal species. These environmental changes have probable impacts on the diet and long‐chain PUFA content of primary consumers. However, herbivorous zooplankton may preferentially retain PUFAs through diet selection for optimal growth and reproduction, but such selective feeding is challenging to document in nature owing to the difficulties in quantifying zooplankton diet.
Here, we sampled seston and herbivorous cladocerans (Daphnia sp. and Bosmina sp.) from lakes (n = 23) in Finland along eutrophication (total phosphorous) and browning gradients (dissolved organic carbon DOC). We analysed the fatty acid content of seston (mg FA/g POC particular organic content) and cladocerans (mg FA/g C), and estimated available and consumed diet biomass percentages with quantitative fatty acid signature analysis. Cladoceran diet preference was evaluated as the difference between consumed and available food sources, to understand if they preferentially retain high nutritional quality diet.
Generally, lake chemistry and morphometry poorly explained seston and cladoceran long‐chain PUFA contents. However, multiple linear models for shorter chain PUFAs (linoleic acid LA and alpha‐linolenic acid ALA) performed better in explaining variation in the LA and ALA content of seston (20% and 11%) and cladocerans (36% and 46%, respectively). The factors most strongly and positively associated with the LA and ALA content of seston and cladocerans were phosphorus and DOC concentrations, respectively.
Seston and cladoceran PUFA contents were clearly uncorrelated. In most of the sampled lakes, high‐quality diet (i.e., diatoms and cryptomonads) was preferred by cladocerans and low‐quality diet (cyanobacteria) was avoided. Lake chemistry poorly explained cladoceran diet preference, but high‐quality preference was positively associated with lake average depth.
In summary, our space‐for‐time study approach did not reveal that eutrophication or browning downgraded the seston nor cladoceran PUFA quality. We found no correlation with seston and cladoceran PUFA content, but a clear mismatch between available and consumed diet. Our results suggest a selective feeding strategy of cladocerans, possibly through foraging in high‐quality algae patches or selective assimilation of PUFAs.
Microplastic fibers (MPF) are a ubiquitous marine contaminant, making up to 90% of global microplastic concentrations. Imaging flow cytometry was used to measure uptake and ingestion rates of MPF by ...blue mussels (Mytilus edulis). Mussels were fed a diet of Rhodomonas salina and MPF concentrations up to 30 MPF mL−1, or 0.374% of available seston. Filtration rates were greatly reduced in mussels exposed to MPF. Uptake of MPF followed a Holling's Type II functional response with 95% of the maximum rate (5227 MPF h−1) occurring at 13 MPF mL−1. An average of 39 MPF (SE ± 15, n = 4) was found in feces (maximum of 70 MPF). Most MPF (71%) were quickly rejected as pseudofeces, with approximately 9% ingested and <1% excreted in feces. Mussels may act as microplastic sinks in Gulf of Maine coastal waters, where MPF concentrations are near the order of magnitude as the experimental treatments herein.
•Mussels take up MPF in a quantifiable and predictable manner.•MPF depress the mussel's filtration rate of microalgal prey at levels >3 MPF mL−1.•Most MPF within the body resided in the digestive gland, with less in the gill.•MPF are lost through pseudofeces and feces, with 60% of body load gone in 9 h.
Methylmercury (MeHg) transfer from water into the base of the food web (bioconcentration) and subsequent biomagnification in the aquatic food web leads to most of the MeHg in fish. But how important ...is bioconcentration compared to biomagnification in predicting MeHg in fish? To answer this question we reviewed articles in which MeHg concentrations in water, plankton (seston and/or zooplankton), as well as fish (planktivorous and small omnivorous fish) were reported. This yielded 32 journal articles with data from 59 aquatic ecosystems at 22 sites around the world. Although there are many case studies of particular aquatic habitats and specific geographic areas that have examined MeHg bioconcentration and biomagnification, we performed a meta-analysis of such studies. Aqueous MeHg was not a significant predictor of MeHg in fish, but MeHg in seston i.e., the base of the aquatic food web, predicted 63% of the variability in fish MeHg. The MeHg bioconcentration factors (i.e., transfer of MeHg from water to seston; BCFw-s) varied from 3 to 7 orders of magnitude across sites and correlated significantly with MeHg in fish. The MeHg biomagnification factors from zooplankton to fish varied much less (logBMFz-f, 0.75 ± 0.31), and did not significantly correlate with fish MeHg, suggesting that zooplanktivory is not as important as bioconcentration in the biomagnification of fish MeHg across the range of ecosystems represented in our meta-analysis. Partial least square (PLS) and linear regression analyses identified several environmental factors associated with increased BCF, including low dissolved organic carbon, low pH, and oligotrophy. Our study reveals the widespread importance of MeHg bioconcentration into the base of the aquatic food web for MeHg at higher trophic levels in aquatic food webs, as well as the major influences on the variability in this bioconcentration.
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•Extensive MeHg bioaccumulation literature review and meta-analysis•MeHg bioconcentration factors at food web base predict preyfish MeHg.•DOC and trophic status influence MeHg bioconcentration factors.•MeHg concentration in water column does not predict MeHg in biota.•Conceptualization of a MeHg BCF elevator leading to a BMF staircase
Extreme precipitation is occurring with greater frequency and intensity as a result of climate change. Such events boost the transport of allochthonous organic matter (allo-OM) to freshwater ...ecosystems, yet little is known about the impacts on dissolved organic matter (DOM) quality and seston elemental stoichiometry, especially for lakes in warm climates. A mesocosm experiment located in a Turkish freshwater lake was designed to simulate a pulse event leading to increased inputs of allo-OM by examining the individual effects of increasing water colour (HuminFeed®, HF), the direct effects of the extra energetic inputs (alder tree leaf leachate, L), and the interactions of the single treatment effects (combination of both sources, HFL), along with a comparison with unmanipulated controls. Changes in the DOM quality and nutrient stoichiometry of the allo-OM treatment additions was examined over the course of the experiments. Results indicated that there was an increase of high recalcitrant DOM components in the HF treatment, in contrast to an increase in less aromatic microbially derived molecules for the L treatment. Unexpectedly, seston C:P ratios remained below a severe P-limiting threshold for plankton growth and showed the same temporal pattern in all mesocosms. In contrast, seston N:P ratios differed significantly between treatments, with the L treatment reducing P-limiting conditions, whilst the HF treatment increased them. The effects of the combined HFL treatment indicated an additive type of interaction and chlorophyll-
a
was highest in the HFL treatment. Our results demonstrate that accounting for the optical and stoichiometric properties of experimental allo-OM treatments is crucial to improve the capacity to explain extrapolated conclusions regarding the effects of climate driven flooding on freshwater ecosystems in response to global climate change.
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•analysis of mineralogical and organic composition of riverine suspended matter.•identification of key components governing freshwater floc formation.•phyllosilicates, iron oxides/(oxy)hydroxides & ...microbial exopolymers are key.•they enhance physicochemical surface heterogeneities and consequently flocculation.•floc formation mechanisms and dynamics in composition and morphology explained.
Freshwater suspended particulate matter (SPM) plays an important role in many biogeochemical cycles and serves multiple ecosystem functions. Most SPM is present as complex floc-like aggregate structures composed of various minerals and organic matter from the molecular to the organism level. Flocs provide habitat for microbes and feed for larger organisms. They constitute microbial bioreactors, with prominent roles in carbon and inorganic nutrient cycles, and transport nutrients as well as pollutants, affecting sediments, inundation zones, and the ocean. Composition, structure, size, and concentration of SPM flocs are subject to high spatiotemporal variability. Floc formation processes and compositional or morphological dynamics can be established around three functional components: phyllosilicates, iron oxides/(oxy)hydroxides (FeOx), and microbial extracellular polymeric substances (EPS). These components and their interactions increase heterogeneity in surface properties, enhancing flocculation. Phyllosilicates exhibit intrinsic heterogeneities in surface charge and hydrophobicity. They are preferential substrates for precipitation or attachment of reactive FeOx. FeOx form patchy coatings on minerals, especially on phyllosilicates, which increase surface charge heterogeneities. Both, phyllosilicates and FeOx strongly adsorb natural organic matter (NOM), preferentially certain EPS. EPS comprise various substances with heterogeneous properties that make them a sticky mixture, enhancing flocculation. Microbial metabolism, and thus EPS release, is supported by the high adsorption capacity and favorable nutrient composition of phyllosilicates, and FeOx supply essential Fe.
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The seasonal migration of a salt wedge and rainfall were the major factors influencing the spatiotemporal distribution of ichthyoplankton and microplastics along the main channel of the Goiana ...Estuary, NE Brazil. The most abundant taxa were the clupeids Rhinosardinia bahiensis and Harengula clupeola, followed by the achirid Trinectes maculatus (78.7% of the catch). Estuarine and mangrove larvae (e.g. Anchovia clupeoides, Gobionellus oceanicus), as well as microplastics were ubiquitous. During drier months, the salt wedge reaches the upper estuary and marine larvae (e.g. Cynoscion acoupa) migrated upstream until the zones of coastal waters influence. However, the meeting of waterfronts in the middle estuary forms a barrier that retains the microplastics in the upper and lower estuary most part of the year. During the late dry season, a bloom of zooplankton was followed by a bloom of fish larvae (12.74 ind. 100 m−3) and fish eggs (14.65 ind. 100 m−3) at the lower estuary. During the late rainy season, the high freshwater inflow flushed microplastics, together with the biota, seaward. During this season, a microplastic maximum (14 items 100 m−3) was observed, followed by fish larvae maximum (14.23 ind. 100 m−3) in the lower estuary. In contrast to fish larvae, microplastics presented positive correlation with high rainfall rates, being more strictly associated to flushing out/into the estuary than to seasonal variation in environmental variables. Microplastics represented half of fish larvae density. Comparable densities in the water column increase the chances of interaction between microplastics and fish larvae, including the ingestion of smaller fragments, whose shape and colour are similar to zooplankton prey.
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•Salt wedge and rainfall influenced the distribution of plankton and microplastics.•Microplastics represented half of fish larvae density.•High freshwater inflow flushed microplastics and the biota seaward.•Interactions between microplastics and fish larvae are increasing.•Ingestion of microplastics might cause gut blockage and induce starvation.
Concerns are being raised that microplastic pollution can have detrimental effects on the feeding of aquatic invertebrates, including zooplankton. Both small plastic fragments (microplastics, MPs) ...produced by degradation of larger plastic waste (secondary MPs; SMPs) and microscopic plastic spheres used in cosmetic products and industry (primary MPs; PMPs) are ubiquitously present in the environment. However, despite the fact that most environmental MPs consist of weathered plastic debris with irregular shape and broad size distribution, experimental studies of organism responses to MP exposure have largely used uniformly sized spherical PMPs. Therefore, effects observed for PMPs in such experiments may not be representative for MP-effects in situ. Moreover, invertebrate filter-feeders are generally well adapted to the presence of refractory material in seston, which questions the potential of MPs at environmentally relevant concentrations to measurably affect digestion in these organisms. Here, we compared responses to MPs (PMPs and SMPs) and naturally occurring particles (kaolin clay) using the cladoceran Daphnia magna as a model organism. We manipulated food levels (0.4 and 9 μg C mL-1) and MP or kaolin contribution to the feeding suspension (<1 to 74%) and evaluated effects of MPs and kaolin on food uptake, growth, reproductive capacity of the daphnids, and maternal effects on offspring survival and feeding. Exposure to SMPs caused elevated mortality, increased inter-brood period and decreased reproduction albeit only at high MP levels in the feeding suspension (74% by particle count). No such effects were observed in either PMP or kaolin treatments. In daphnids exposed to any particle type at the low algal concentration, individual growth decreased by ~15%. By contrast, positive growth response to all particle types was observed at the high algal concentration with 17%, 54% and 40% increase for kaolin, PMP and SMP, respectively. When test particles comprised 22% in the feeding suspension, both MP types decreased food intake by 30%, while kaolin had no effect. Moreover, SMPs were found to homoaggregate in a concentration-dependent manner, which resulted in a 77% decrease of the ingested SMPs compared to PMPs. To better understand MP-processing in the gut, gut passage time (GPT) and evacuation rate of MPs were also assayed. SMPs and PMPs differed in their effects on daphnids; moreover, the particle effects were dependent on the MP: algae ratio in the suspension. When the MP contribution to the particle abundance in the medium changed from 1 to 4%, GPT for daphnids exposed to SMPs increased 2-fold. Our results suggest that MPs and, in particular, SMPs, have a greater capacity to negatively affect feeding in D. magna compared to naturally occurring mineral particles of similar size. Moreover, grazer responses observed in experiments with PMPs cannot be extrapolated to the field where SMPs dominate, because of the greater effects caused by the latter.
Two live feed relevant copepods for larval fish and shrimps, Pseudodiaptomus annandalei and Apocyclops royi, were predominant year-round in a tropical brackish fishpond system. The ponds environment ...is harsh concerning physicochemical properties; temperature 20-32 °C, salinity 15-23 besides abrupt salinity drops 15-9, frequent severe hypoxia, and poor nutritional seston quality. In 50 studies investigating several physiological endpoints, P. annandalei performs optimally within 18-32 °C and salinity 10-30 and A. royi within 24-32 °C and salinity 10-32. Most extreme, A. royi is reported in situ at salinity 50 and in the laboratory; it can adjust from salinity 20 to freshwater within just two generations when fed on Baker's yeast. Both species and in particular A. royi have developed an outstanding capability to convert ingested seston with poor fatty acid composition into the necessary long-chained polyunsaturated fatty acids (PUFAs) characterizing their tissues. Hence, they self-enrich their bodies' fatty acid profiles. Their physiological plasticity is likely a prerequisite for existing extensive mass production in the harsh pond environment. Moreover, A. royi exhibit additional traits, that is, high density tolerance qualifying also for intensive mass production suggesting it as the most promising live feed of the two species for fish and shrimp hatcheries.
Rivers are a major source of microplastic particles (<5 mm) to oceans, but empirical measurements of microplastic movement in freshwater ecosystems are rare. The hard, buoyant surface of microplastic ...is a novel habitat that selects for unique microbial assemblages in rivers, especially downstream of wastewater treatment plant (WWTP) point sources. We measured microplastic in surface water and benthic habitats 50 m upstream and 50, 305, 1115, and 1900 m downstream of the effluent outfall from a large WWTP in an urban river. We used high-throughput sequencing to measure bacterial assemblages on microplastic from surface and benthic habitats and compared them to bacterial assemblages from seston, water, and sediment. Concentrations of total microplastic and microplastic types (fragment, pellet) in surface water did not change with distance downstream of the WWTP. Thus, microplastic transport showed no net deposition or resuspension. Microplastic concentrations were much higher in the benthic zone than surface water. Benthic deposition appears to be a plastic sink over longer time scales, but subsequent studies are needed to resolve microplastic transport dynamics by particle type, size, and habitat. Composition of microplastic-attached bacterial assemblages differed from that of assemblages in water, seston, and sediment and supports domestic wastewater as a point source of microplastic (e.g., gastrointestinal taxa). Shifts in microplastic assemblages with distance from the WWTP suggest succession toward a ‘stream-like’ bacterial assemblage. Future studies are required to quantify the metabolic capacity of microplastic-associated bacteria. Estimates of transport distance, microplastic storage, and microbial interactions are critical to include lotic ecosystems in accountings of global plastic budgets.
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