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Competition between cyanobacteria and green algae affects phytoplankton succession and the well-known cyanobacteria blooms. Climate warming and water acidification are two concerned environmental issues changing the freshwater ecosystems. To investigate the competitive responses of phytoplankton to warming and acidification, we co-cultured Microcystis aeruginosa and Scenedesmus obliquus at a temperature range of 15–35 °C and a pH range of 5–9. Results showed that S . obliquus was superior competitor at 15 °C. At 20–30 °C, the populations of both Scenedesmus and Microcystis were inhibited by the presence of each other. S . obliquus was in competitive domination at the initial phase of cultivation, but was finally replaced by M . aeruginosa . Microcystis kept competition advantage at 35 °C, whereas Scenedesmus outcompeted Microcystis at acidic conditions (pH ≤ 6). Neutral and weakly alkaline conditions (pH 7–9) supported the replacement of competition domination from Scenedesmus to Microcystis . The present study revealed that climate warming may accelerate the phytoplankton succession from green algae to cyanobacteria, with the predicted promoted cyanobacteria blooms. Nonetheless, water acidification causes Microcystis to be a weak competitor with green algae, suggesting that the advantageous effect of Microcystis toward green algae at high temperatures was controlled by other variables like the water pH.

Nanoparticles of zinc oxide (ZnO NPs) are extensively used in various applications, and their widespread use leads to their environmental presence, particularly in wastewater treatment plant effluents, rivers, and soil. This study focuses on the obscure puffer, Takifugu obscurus, an economically important fish in China, aiming to assess the toxic effects of ZnO NPs on its early life stages, emphasizing the need for understanding the ecological implications of ZnO NP exposure in aquatic environments. Exposure during the hatching stage resulted in a significant decrease in hatching rates, with embryos displaying surface coating at higher ZnO NP concentrations. Newly hatched larvae experienced deformities, and post-hatching exposure led to pronounced reductions in survival rates, particularly with higher ZnO NP concentrations. Two-month-old juveniles exposed to increasing ZnO NP concentrations exhibited a consistent decline in survival rates, emphasizing concentration-dependent adverse effects. Biochemical analyses revealed elevated malondialdehyde (MDA) levels and decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) activities in various tissues, indicating oxidative stress. This study underscores the ecological risks of ZnO NP contamination in aquatic environments, emphasizing the need for careful consideration of nanoparticle exposure in aquatic ecosystems.

Quinolone antibiotic (QA) residues in various natural environments have recently received massive scientific attention. Nevertheless, there is limited information on the distribution characteristics and potential hazards of antibiotics in coastal wetlands. Here, the occurrence, spatial and seasonal distribution, and ecological risk assessment of eight QAs including pipemidic acid (PPA), ofloxacin (OFL), enrofloxacin (ENR), ciprofloxacin (CIP), sarafloxacin (SAL), lomefloxacin (LOM), flumequine (FLU), and oxolinic acid (OA) in coastal wetland were investigated through collected water, sediment, benthos, and plant samples along the Jiangsu coastline in four seasons. The results demonstrated that all selected QAs were detected with varying frequencies and degrees, and their mean concentrations in water, sediment, plants, and benthos ranged from n.d. to 6.11 ng L−1, 3.10 μg kg−1, 6.14 μg kg−1, and 17.13 μg kg−1, respectively. The seasonal differences in antibiotic concentration indicated higher values in winter and significantly lower values in summer, while no significant variations were observed between spring and autumn. Based on the risk quotient (RQ) method, the ecological risk assessment revealed medium risks for OFL, ENR, CIP, and LOM, and low or no risks of other QAs. It is suggested that the differences in PNEC values between seasons and toxicity of antibiotic mixtures should be considered in future studies for better illustration of actual risk levels. This research provides fundamental data and an assessment pattern that governments and other scientific groups all over the world could use as reference to evaluate QA residues in coastal wetlands.

Microplastics represent an emerging threat to aquatic environments and organisms, as they infiltrate water systems, are ingested by marine species, and cause physical harm, endocrine disruption, and bioaccumulation up the food chain, potentially impacting biodiversity and human health. Aquatic ecosystems face considerable harm from microplastic pollution because fish in the early developmental stages, including embryos, larvae, and juveniles, are more susceptible due to their immature physiological and detoxification systems. This review aims to comprehensively explore the impacts of microplastics on the early life stages of fish. Aquatic environments receive primary and secondary MPs from urban runoff and industrial waste, together with degraded plastics, which affect fish embryos and larvae via direct ingestion, surface adhesion, and trophic transmission pathways. The physical impact of MPs causes digestive tract blockages that reduce hatching success and create developmental problems in fish organs, but chemical toxicity develops from plasticizers, heavy metal leaching, and pollutant adsorption, which causes oxidative stress, endocrine disruption, and metabolic dysfunction. Survival rates decrease because exposure causes fish to perform poorly during swimming activities and make limited efforts to avoid predators. The small dimensions and high chemical reactivity of MPs increase their bioavailability, which promotes tissue penetration and leads to accumulation at different levels of the food chain. This comprehensive review emphasizes that we need to establish uniform detection protocols, long-term exposure research, and effective strategies to control MP pollution. The resolution of these difficulties remains essential for protecting fish populations, as well as for protecting biodiversity and minimizing seafood contamination risks to human health.

Suitable temperature and light intensity play important roles in the formation of harmful algae blooms (HABs), which can pose serious threats to aquatic ecosystems and human health. In this study, we measured the growth, physiological function, and paralytic shellfish toxins (PSTs) production of Alexandrium pacificum (CCMA-272), a strain isolated from East China Sea, at different temperatures (15, 20, and 25 °C) and light intensities (30, 60, and 90 µmol photons/(m 2 ·s)). Results indicate that temperature and light intensity significantly affected the growth, physiology, and toxigenic potentials of A. pacificum . The optimal conditions for the growth of A. pacificum were observed at 20 °C under 60 µmol photons/(m 2 ·s). Regarding the production of PSTs, this strain of A. pacificum produced 12 PSTs, including carbamate toxins: saxitoxin (STX), neosaxitoxin (NEO), and gonyautoxin 1–4 (GTX1, GTX2, GTX3, GTX4); dicarbamoyl toxins: dicarbamoylsaxitoxin (dcSTX), dicarbamoylgonyautoxin 2, 3 (dcGTX2, dcGTX3); and N-sulfocarbamoyl toxins: N-sulfocarbamoylgonyautoxin 1, 2 (C1, C2), and gonyautoxin 5 (GTX5). Among all the PSTs, C2 was the most abundant. Low temperature (15 °C) and high light intensity (90 µmol photons/(m 2 ·s)) were beneficial for the production of PSTs in A. pacificum. When cultured at 20 and 25 °C, A. pacificum generated comparable total quantities of PSTs, yet the toxicity levels were lower at 25 °C. Intracellular PSTs contents were greater than extracellular PSTs contents, except those under the condition of 25 °C with 30 µmol photons/(m 2 ·s). However, as the increase of temperature, A. pacificum released more amounts of analogues with higher toxicity levels (e. g., STX and dcGTX 2 ) into the environment than intracellularly. These findings emphasize the significant sensitivity of A. pacificum to temperature and light intensity, highlighting the importance of evaluating both intracellular and extracellular PSTs for assessing its toxicity and aiding in the prediction and management of HABs.

Freshwater salinization is a growing environmental issue caused by various anthropic or natural factors that lead to changes in water chemistry and physical conditions, affecting the survival and diversity of phytoplankton. In this study, we tested the physiological, morphological and interspecific competition of the freshwater cyanobacterium Microcystis aeruginosa and the green algae Scenedesmus obliquus to salinity stress. Results demonstrated that increasing salinity had a significant negative effect on the growth of M. aeruginosa and S. obliquus. M. aeruginosa showed a decline in growth rate with increasing salinity, while S. obliquus showed a lower growth rate under salinity stress but with no significant difference between the two salinity groups. In cocultures, S. obliquus outcompeted M. aeruginosa, and the displacement was accelerated with increasing salinity. The photosynthetic performance of both algae was affected by salinity, the presence of competitors, and the cultivation time. S. obliquus showed morphological variations under salinity stress and the presence of a competitor. The study suggests that salinity stress and competition can have a significant impact on the growth and performance of algae species. The findings of our study suggest that the salinization of freshwater can impact the interspecific interactions among phytoplankton, which play a crucial role in the functioning of freshwater ecosystems.

Increased temperature accelerates vital rates, influencing microbial population and wider ecosystem dynamics, for example, the predicted increases in cyanobacterial blooms associated with global warming. However, heterotrophic and mixotrophic protists, which are dominant grazers of microalgae, may be more thermally sensitive than autotrophs, and thus prey could be suppressed as temperature rises. Theoretical and meta-analyses have begun to address this issue, but an appropriate framework linking experimental data with theory is lacking. Using ecophysiological data to develop a novel model structure, we provide the first validation of this thermal sensitivity hypothesis: increased temperature improves the consumer’s ability to control the autotrophic prey. Specifically, the model accounts for temperature effects on auto- and mixotrophs and ingestion, growth and mortality rates, using an ecologically and economically important system (cyanobacteria grazed by a mixotrophic flagellate). Once established, we show the model to be a good predictor of temperature impacts on consumer–prey dynamics by comparing simulations with microcosm observations. Then, through simulations, we indicate our conclusions remain valid, even with large changes in bottom-up factors (prey growth and carrying capacity). In conclusion, we show that rising temperature could, counterintuitively, reduce the propensity for microalgal blooms to occur and, critically, provide a novel model framework for needed, continued assessment.

Fish can maintain a stable intracellular concentration of ions in environments of variable salinities through osmoregulation. In this study, we focused on obscure puffer Takifugu obscurus ( T. obscurus ), an anadromous fish with high commercial value and rapid depression of wide populations, to investigate changes at molecular and physiological levels underlying salinity tolerance through multifaceted analyses integrating transcriptomics and micrography. We found that with the increase of salinity, the structure of the three main osmoregulation organs, i.e., gill, intestine, and kidney had remarkable changes. The results of transcriptome demonstrated that the ATP-binding box transporter and cyclic adenosine monophosphate (cAMP) signaling pathway in the gill and kidney were significantly reduced. Growth hormone, prolactin, and cortisol regulated more transporters of body composition and stimulated chloride cell proliferation and differentiation, which change the capacity for membrane transport between ion and water molecules. Adenosine-activating protein kinase and thyroid hormone signaling pathway were also significantly upregulated. These transcriptional levels changes of T. obscurus combined with ultrastructure in response to salinity increase indicated that osmoregulation is a complex process involving multiple organs and signaling pathways. Overall, this study can deepen the understanding of osmotic regulation during fish migration.

For the freshwater phytoplankton Scenedesmus , morphological defense induced by infochemicals released from grazers (such as Daphnia ) is considered to be a defensive strategy. In this study, we investigated the response of Scenedesmus obliquus to long-term repeated grazing infochemicals exposure, with two stimulation intervals (short period of 4 days and long period of 7 days per round). Results demonstrated that the defensive response of S. obliquus gradually degenerated with periodically repeated exposure to Daphnia infochemicals and the degeneration rate was positively correlated with stimulation frequency, that is, shorter intervals caused a faster decrease in average algal colony size. According to nonlinear regression fitting, a harmonic oscillator function with exponential attenuation could be applied to illustrate S. obliquus morph changes, with which the growth rate was positively correlated. Our study suggests that the optimal defensive colony size in S. obliquus might depend on trade-offs between its anti-grazing defense and other functions. This insight contributes to the understanding of algal inducible defense mechanism, serving as a complement to the optimal defense theory. Additionally, long-term periodic grazing threats without causing concrete damage may disrupt feedback mechanisms and real biomass loss is assumed to be an important precondition for sustaining enduring defensive phenotypes.

Atmospheric CO₂ level is increasing and considerably influences aquatic ecosystems. Grazer-induced defenses in phytoplankton stabilize the structures of aquatic food webs. Costs associated with defense have resulted in a situation in which the effectiveness of inducible defenses depends on environmental conditions. To investigate the grazer-induced defense responses to elevated air CO₂ levels, the algae Scenedesmus obliquus was cultured under two air CO₂ concentrations (390 ppm and 750 ppm) in the absence or presence of predator-derived cues (Daphnia filtrate). In response to Daphnia filtrate, colonial populations such as eight-celled colony were largely formed in S. obliquus. When air CO₂ was elevated to 750 ppm, the inorganic carbon contents in media increased, thereby stimulating algal reproduction and photosynthesis. Moreover, the volumes of unicells and two-celled colonies were enlarged under elevated CO₂ conditions. These physiological changes satisfied the material and energy demands for the formation of larger colonies. Based on the consistent surface area per volume of the large colony under ambient and elevated CO₂ conditions, the increased inorganic carbon (by CO₂ enrichment) facilitated the carbon uptake of the multi-celled colony. Thus, the morphological defense in phytoplankton was enhanced with more eight-celled colonies formed in populations grown in a high-CO₂ environment. The present result verified the hypothesis that inducible defense is less costly and has higher effectiveness with increasing carbon availability. The enhancement of anti-grazer morphological defenses in phytoplankton potentially alters the trophic cascades between phytoplankton and zooplankton and contributes to the redirected energy and nutrient flow in ecosystem-level processes under a CO₂-rising climate.