In this study, we conducted a 14-month investigation in Daya Bay, southern China to understand the effects of oyster farming on phytoplankton community and biomass by using size-fractionated phytopigments. Results proved the filtering effects of oysters on phytoplankton biomass. During the oyster culture period, the average concentration of total chlorophyll a (sum of size-fractionated Chl a) within the farming area was approximately 60% lower than that at the reference site. Phytoplankton depletion in the aquaculture zone mainly occurred in micro-sized fractions (>20 μm) of Chl a, fucoxanthin, and peridinin. The influence of oyster filtration on nano-sized (2.7–20 μm) pigments seemed less than that on micro-sized ones. The depletion of peridinin and 19′-hex-fucoxanthin in aquaculture zone was higher than those of the other pigments, which indicated that flagellated cells might be selectively filtered by oysters and could be more easily influenced by oyster aquaculture. The pico-sized Chl a (<2.7 μm) comprised 24% of total Chl a on the average in the aquaculture zone during the cultural period compared to 6% in the reference site. Picoeukaryote abundance, which was determined via flow cytometry, was significantly higher in the aquaculture zone than in the non-aquaculture areas. The abundance of picoeukaryote is significantly and positively correlated with the concentrations of pico-sized prasinoxanthin, violaxanthin, and neoxanthin, indicating that picoeukaryote is dominated by those in prasinophyte. The results suggest that oyster aquaculture might stimulate the growth of prasinophyte, although the seasonal variations are mainly controlled by the water temperature in the study area. This research highlights the successful use of size-fractionated phytopigments to estimate size-specific phytoplankton biomass and community, which can be applied as a routine method to monitor the environmental effect and food resources of bivalve aquaculture.

Although fluoride occurs naturally in the environment, excessive amounts of fluoride in freshwater and terrestrial ecosystems can be harmful. We evaluated the toxicity of fluoride compounds on the growth, viability, and photosynthetic capacity of freshwater (Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) and terrestrial (Chlorococcum infusionum) algae. To measure algal growth inhibition, a flow cytometric method was adopted (i.e., cell size, granularity, and auto-fluorescence measurements), and algal yield was calculated to assess cell viability. Rhodamine123 and fluorescein diacetate were used to evaluate mitochondrial membrane potential (MMA, ΔΨm) and cell permeability. Nine parameters related to the photosynthetic capacity of algae were also evaluated. The results indicated that high concentrations of fluoride compounds affected cell viability, cell organelle potential, and photosynthetic functions. The cell viability measurements of the three algal species decreased, but apoptosis was only observed in C. infusionum. The MMA (ΔΨm) of cells exposed to fluoride varied among species, and the cell permeability of the three species generally decreased. The decrease in the photosynthetic activity of algae may be attributable to the combination of fluoride ions (F−) with magnesium ions (Mg2+) in chlorophyll. Our results therefore provide strong evidence for the potential risks of fluoride compounds to microflora and microfauna in freshwater and terrestrial ecosystems.

This study investigates different UV doses (mJ/cm2) and the effect of dark incubation on the survival of the algae Tetraselmis suecica, to simulate ballast water treatment and subsequent transport.Samples were UV irradiated and analyzed by flow cytometry and standard culturing methods. Doses of ≥400mJ/cm2 rendered inactivation after 1day as measured by all analytical methods, and are recommended for ballast water treatment if immediate impairment is required. Irradiation with lower UV doses (100–200mJ/cm2) gave considerable differences of inactivation between experiments and analytical methods. Nevertheless, inactivation increased with increasing doses and incubation time. We argue that UV doses ≥100mJ/cm2 and ≤200mJ/cm2 can be sufficient if the water is treated at intake and left in dark ballast tanks. The variable results demonstrate the challenge of giving unambiguous recommendations on duration of dark incubation needed for inactivation when algae are treated with low UV doses.

Hypoxia often intensifies with rising dissolved CO2, but the concurrent effects of hypoxia and acidification on bivalves are largely unknown. In this study, immune responses of hemocytes in the mussel Mytilus coruscus were examined under six combinations of pH (7.3, 7.7 and 8.1) and dissolved oxygen (DO) concentrations (2mgL−1, 6mgL−1) for 72h. Generally, total hemocyte account, phagocytosis, esterase and lysosomal content were reduced under low DO and pH conditions, whereas hemocyte mortality and reactive oxygen species production increased under low DO and pH. Both hypoxia and low pH have negative effects on mussels, but the effects of pH are not as strong as DO. Moreover, significant interactions between DO and pH occurred. However, acidification generally doesn't aggravate the effects induced by hypoxia. Acidification and hypoxia may increase disease risk and impact the aquaculture of this species.

Tropical shrimp aquaculture systems in New Caledonia regularly face major crises resulting from outbreaks of Vibrio infections. Ponds are highly dynamic and challenging environments and display a wide range of trophic conditions. In farms affected by vibriosis, phytoplankton biomass and composition are highly variable. These conditions may promote the development of harmful algae increasing shrimp susceptibility to bacterial infections. Phytoplankton compartment before and during mortality outbreaks was monitored at a shrimp farm that has been regularly and highly impacted by these diseases. Combining information from flow cytometry, microscopy, pigment and phylogenetic analysis, the presence of Picocyanobacteria, Prasinophyceae and Diatomophyceae were detected as dominant phytoplankton groups and Cryptophyceae, Prymnesiophyceae and Dinophyceae as minor components. At the onset of the first shrimp mortalities, Bacillariophyceae increased while Cyanobacteria, Prymnesiophyceae and Dinophyceae decreased in the water column, followed by proliferation of Prasinophyceae. Several taxa were identified as potential harmful algae (Cyanobacteria, dinoflagellates and Phaeocystis).

Flow cytometry was applied to assess the microbiological impact of treated sewage effluent discharge into a small brook carrying surface runoff water. Increases in dissolved organic carbon and soluble reactive phosphorous were accompanied by increases in counts of intact bacteria by up to eightfold. Effluent ingress furthermore resulted in a pronounced shift of bacterial clusters. Whereas brook water upstream of the discharge point was characterised by a bacterial cluster with low nucleic acid (LNA) content, downstream water showed a shift to bacteria with high nucleic acid (HNA) content. Changes in the LNA/HNA ratio were largely maintained along the course of the brook. Results suggest that the LNA/HNA ratio can under certain conditions serve as an indicator of anthropogenic nutrient impact. Measuring impact on this low trophic level might be more sensitive and straightforward than measuring macroindicators. More evidence will however be required to assess the usefulness of LNA/HNA measurements to assess the ecological nutrient status of natural waters and the impact of nutrient pollution.

The authors investigated the microbial composition of phototrophic biofilms proliferating in a show cave using flow cytometry for the first time in such a context. Results are based on several biofilms sampled in the Moidons Caves (France) and concern both heterotrophic prokaryotes and autotrophic microorganisms. Heterotrophic microorganisms with low nucleic acid content were dominant in biofilms, as can be expected from the oligotrophic conditions prevailing within the cave. Analysis of the biofilm autotrophic components revealed the presence of several taxa, particularly the unicellular green algae Chlorella minutissima, specifically well adapted to this cave. Relationships between flow cytometry results and environmental variables determined in the cave were established and discussed so as to better understand biofilm proliferation processes in caves.

Harmful cyanobacteria bloom contributes to economic loss as well as the threat to human health. Agricultural waste products, particularly straw, have been used to control bloom while arbor plant is the potential candidate for limiting antialgal activity. This study investigated the use of Dracontomelon duperreanum defoliation extract (DDDE) to inhibit the activity of Microcystis aeruginosa. The primary goal of the research was to explore the solution to control cyanobacterial bloom. The photosynthetic activity, cell morphology, membrane integrity, and esterase activity of M. aeruginosa were determined using phytoplankton analyzer pulse amplitude modulation (Phyto-PAM) and flow cytometry before and after exposure to DDDE. The inhibitory rate of M. aeruginosa was about 99.6 % on day 15 when exposed to 2.0 g L⁻¹. A reduction of chlorophyll a (Chl-a) activity and changes in cell membrane suggested the algistatic property of DDDE. Inhibition of photosynthetic activity was reflected by changing mean Chl-a fluorescence intensity (MFI) which was about 52.5 % on day 15 when exposed to 2.0 g L⁻¹ DDDE as well as relative electron transport rates (rETRs) of algal cell. These changes might contribute to the suppression of M. aeruginosa. Algal cell exposed to DDDE may lead to cell volume reduction or slow growth. This resulted in a decreased proportion of normal or swollen granular cells after DDDE treatment.

Current tools to predict biofilm thickness and viability in spatial distribution are poor, especially those based on chemical oxygen demand (COD), total nitrogen (TN), and total phosphate (TP) due to their limited data and complex calculations. Here, support vector regression (SVR) was used to predict biofilm thickness and viability in a reactor filled with carriers of crushed stone globular aggregates. Analyses combined confocal laser scanning microscopy and flow cytometry with Kriging interpolation revealed that biofilm thickness varied from 22 to 31 μm, and biofilm viability decreased from 80 to 30 % in the flow direction of the reactor. The biofilm thickness at the bottom was thicker than that in the upper layer, but biofilm viability contrasted with biofilm thickness in the vertical distribution. The values of biofilm thickness and viability were predicted at a layer 35 cm from the bottom of the reactor with mean squared error values of 0.014 and 0.011, respectively. Correlation coefficients were 0.996 and 0.997 between carbon-nitrogen-phosphorus (C–N–P) removal with biofilm thickness and viability in spatial distribution, respectively. This study provided an important mathematical method to predict biofilm thickness and viability in spatial distribution based on the concentration of C–N–P.

As cadmium may be involved in the etiology of head and neck cancers, we investigated in the present work, the cytotoxic and genotoxic effects of Cd on human larynx cells. SQ20B cells were exposed to 25 and 50 μM Cd for 48 and 72 h. Results showed a dose-dependent decrease in cell viability, especially after 48 h, associated with mitochondria alterations as showed by transmission electronic microscopy. Surprisingly, the flow cytometry shows that the cells treated with Cd have a normal proliferative cycle like the untreated cell especially in G1 or G2 phase of cell cycle. DNA damages were investigated by comet assay and immunofluorescence for gamma layer of the H2AX (g-H2AX) foci formation. Results show a strong induction of DNA double-strand breaks after Cd exposure. Overall, our results demonstrate the cytotoxicity and genotoxicity of Cd in human larynx cells and support the view that Cd could be an etiologic factor of head and neck cancers.