Influence of salinity on population growth, oxidative stress and antioxidant defense system in the marine monogonont rotifer Brachionus plicatilis

Combined toxic effects of yessotoxin and polystyrene on the survival, reproduction, and population growth of rotifer Brachionus plicatilis at different temperatures

Yessotoxin (YTX) is a disulfated toxin produced by harmful dinoflagellates and causes risks to aquatic animals. Polystyrene (PS) microplastics could absorb toxins in seawaters but pose threats to organism growth. In this study, the combined toxic effects of YTX (0, 20, 50, and 100 µg L-1) and PS (0, 5, and 10 µg mL-1) on the survival, reproduction, and population growth of marine rotifer Brachionus plicatilis at 20 °C, 25 °C, and 30 °C were evaluated. Results indicated that the survival time (S), time to first batch of eggs (Ft), total offspring per rotifer (Ot), generational time (T0), net reproduction rate (R0), intrinsic growth rate (rm), and population growth rate (r) of rotifers were inhibited by YTX and PS at 25 °C and 30 °C. Low temperature (20 °C) improved the life-table parameters T0, R0, and rm at YTX concentrations less than 100 µg L-1. Temperature, YTX, and PS had interactive effects on rotifers' S, Ft, Ot, T0, R0, rm, and r. The combined negative effects of YTX and PS on rotifers' survival, reproduction, and population growth were significantly enhanced at 30 °C. These findings emphasized the importance of environmental temperature in studying the interactive effects of microplastics and toxins on the population growth of zooplankton in eutrophic seawaters.

Multigenerational resilience of the marine rotifer Brachionus plicatilis to high temperature after additive exposure to high salinity and nanoplastics

To study multigenerational resilience to high temperature (HT) conditions, we exposed Brachionus plicatilis marine rotifers to HT, high salinity (HS), and nanoplastics (NPs), and measured reproductive and life-cycle endpoints. After exposure to HT, rotifer lifespans were reduced, but daily production of offspring increased. However, both combined HT/HS and HT/HS/NP exposure led to additional decreases in longevity and reproductive ability; the antioxidant defense mechanisms of the rotifers were also notably upregulated as measured by reactive oxygen species levels. Fatty-acid profiles were reduced in all conditions. In multigenerational experiments, the negative effects of HT dissipated rapidly; however, the effects of HT/HS and HT/HS/NPs required four generations to disappear completely. The findings indicated that B. plicatilis were able to recover from these environmental stressors. This study demonstrated the resilience of aquatic organisms in response to changing environmental conditions and provides insights into the complex interactions of different abiotic stressors.

Changes in life history parameters and expression of key genes of Brachionus plicatilis exposed to a combination of organic and inorganic ultraviolet filters

The increasing use of ultraviolet filters has become an emerging contaminant on the coast, posing potential ecological risks. Rotifers are essential components of marine ecosystems, serving as an association between primary producers and higher-level consumers. These organisms frequently encounter ultraviolet filters in coastal waters. This study aimed to assess the comprehensive effects of organic ultraviolet filters, specifically 2-ethylhexyl-4-methoxycinnamate (EHMC), and inorganic ultraviolet filters, namely, titanium dioxide nanoparticles (TiO2 NPs), on the rotifer Brachionus plicatilis. We exposed B. plicatilis to multiple combinations of different concentrations of EHMC and TiO2 NPs to observe changes in life history parameters and the expression of genes related to reproduction and antioxidant responses. Our findings indicated that increased EHMC concentrations significantly delayed the age at first reproduction, reduced the total offspring, and led to considerable alterations in the expression of genes associated with reproduction and stress. Exposure to TiO2 NPs resulted in earlier reproduction and decreased total offspring, although these changes were not synchronised in gene expression. The two ultraviolet filters had a significant interaction on the age at first reproduction and the total offspring of rotifer, with these interactions extending to the first generation. This research offers new insights into the comprehensive effects of different types of ultraviolet filters on rotifers by examining life history parameters and gene expression related to reproduction and stress, highlighting the importance of understanding the impacts of sunscreen products on zooplankton health.

Suitable Acidified Eggshell Powder Food Promotes Brachionus calyciflorus Growth and Reproduction: From Antioxidant Capacity Insight

Rotifers are natural initial bait for fish larvae in freshwater. Here, the effects of various concentrations of acidified eggshell powder solutions (0, 20, 40, 80, 160, and 320 mg/L) on the growth and reproduction of the rotifer Brachionus calyciflorus were evaluated in culture experiments (11 days). The population density, catalase (CAT) and superoxide dismutase (SOD) activity, and Na and Mg contents in rotifers were significantly higher in the 20-160 mg/L groups than in the control group. A redundancy analysis showed that the Na, Mg, Cr, K, and Ca contents were positively correlated with the rotifer population density and CAT and SOD activity. Furthermore, the generation time and lifespan of F2 rotifers were significantly higher in the 20-40 mg/L treatment groups (82.0 ± 3.7 hr and 162.0 ± 2.7 hr, respectively) than in the control group (64.0 ± 4.0 hr and 128.0 ± 4.0 hr, respectively). Average egg production in F2 rotifers was significantly higher in the 20-80 mg/L treatment groups (15.2 ± 0.7 individuals) than in the control group (11.7 ± 1.2 individuals). These results indicate that 20 mg/L eggshell powder is optimal for growth and reproduction in B. calyciflorus, providing a theoretical basis for using new mineral sources in high-quality open bait for fish larvae.

Salinity-dependent top-down effect of rotifer Brachionus plicatilis on removing harmful alga Phaeocystis globosa

Using appropriate zooplankton to transfer the primary productivity of harmful algae to higher trophic levels through food chain is an eco-friendly mode to remove harmful algae. To assess the top-down efficiency of rotifer removing Phaeocystis and the salinity effect, we adopted a series of salinities to carry out Phaeocystis-rotifer population dynamics and rotifer life-history experiments. Results showed that the time for rotifers to remove Phaeocystis population was the shortest when the salinity was ≤20 ‰. With salinity rising to above 25 ‰, although the clearance time of Phaeocystis population by rotifer was significantly prolonged, ultimately the Phaeocystis population were almost completely eliminated at all salinities. Additionally, rotifer matured and reproduced earlier at low salinity, while high salinity significantly delayed first reproductive time and decreased the total offspring. The above findings are helpful to assess the impacts of external environmental factors on the application of zooplankton to control harmful algae.

Swimming behaviour as an alternative endpoint to assess differences in abiotic stress sensitivities between strains of Brachionus koreanus (Rotifera: Monogononta)

Brachionus plicatilis is a cosmopolitan rotifer used as a model organism in several research areas and as live food in aquaculture. Being a species complex, responses to stressors vary even among strains of the same species and, thus, the responses of one species are not representative of the whole complex. This study aimed to address the effects of extreme salinity ranges, and different concentrations of hydrogen peroxide, copper, cadmium, and chloramphenicol, in two strains of B. koreanus (MRS10 and IBA3) from B. plicatilis species complex, by assessing effects on their survival and swimming capacity. Neonates (0-4 h old) were exposed to the stressors in 48 well-microplates, for 24 and 6 h, to evaluate lethal and behavioural effects, respectively. Tested conditions of chloramphenicol did not show any effects on rotifers. The behavioural endpoint showed to be particularly sensitive to assess the effects of high salinity, hydrogen peroxide, and copper sulfate, as swimming capacity impairment was observed for both strains in the lowest concentrations used in lethal tests. Overall, results showed that IBA3 was more tolerant to the majority of stressors, comparing to MRS10, which may be due to differences in physiological characteristics, highlighting the importance of performing multiclonal experiments. Also, swimming capacity inhibition proved to be a good alternative to the classical lethality tests, being sensitive to lower concentrations and with shorter exposure periods.

Physiological responses of marine Chlorella sp. exposed to environmental levels of triphenyltin

Triphenyltin (TPT) is a herbicide and antifouling agent that has been widely used. After TPT flows into water bodies, it will cause toxic effects on marine life. We evaluated the effect of environmental concentration level (0, 10, 100, and 200 ng/L) on the cell density, antioxidant capability, and photosynthesis-related genes in the marine Chlorella sp. The results showed that 10 and 100 ng/L TPT can promote the growth of marine Chlorella sp., 200 ng/L TPT can inhibit the growth of marine Chlorella sp., and the TPT toxicity was accumulative. The chlorophyll composition changed. The content of chlorophyll a in 100 ng/L and 200 ng/L groups was significantly higher than that in the control group (p < 0.05) in 13 days. The content of chlorophyll b in the 100 ng/L and 200 ng/L groups in 1 day and 13 days was significantly different from that in the control group (p < 0.05). The content of total chlorophyll in the 100 ng/L and 200 ng/L groups in 13 days was higher than that in the control group (p < 0.05). The 200 ng/L group began to suffer oxidative damage on the 12th day, and the pigment protein complex responded to oxidative damage through self-feedback regulation. On the 18th day, chld, cao, psy, rbcS, and rbcL genes were downregulated, and psbA gene was upregulated in the 10 ng/L and 100 ng/L groups, which may be a feedback regulation of self-oxidative damage. This paper analyzed toxicity of environmental levels of TPT to marine Chlorella sp., which provided new data support for the comprehensive evaluation of its marine ecological toxicity.

Environmentally relevant concentrations of mercury inhibit the growth of juvenile silver carp (Hypophthalmichthys molitrix): Oxidative stress and GH/IGF axis

Mercury (Hg) is a global environmental contaminant, and excessive mercury levels in water can adversely affect the growth of fish. Silver carp (Hypophthalmichthys molitrix) is one of the important freshwater aquaculture fish in China, and its natural resources have been critically declining. However, the effects of Hg²⁺ exposure on the growth hormone/insulin-like growth factor (GH/IGF) axis and its toxic mechanism are still unclear. In this study, we systematically evaluated the bioaccumulation, histomorphology, antioxidant status, hormone levels, and GH/IGF axis toxicity of juvenile silver carp after exposure to environmental-related concentrations of Hg²⁺ (0, 0.05, 0.5, 5, and 50 µg/L) for 28 days. Results showed that the Hg²⁺ bioaccumulation in the liver increased with a rise in Hg²⁺ concentration and time of exposure. The body length (BL), body weight (BW), weight growth rate (WGR) and specific growth rate (SGR) all decreased after Hg²⁺ exposure. The serum levels of growth hormones (GH and IGF) and thyroid hormones (T3 and T4) were significantly decreased, and the expressions of GH/IGF axis-related genes were significantly downregulated after 7, 14, and 28 days of Hg²⁺ exposure. Correlations between the growth parameters and growth hormones or expression of genes in GH/IGF axis further suggested that environmentally relevant concentrations of Hg²⁺ could have adverse effects on growth. In addition, with increasing Hg²⁺ exposure, superoxide activities of dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST)and levels of reduced glutathione (GSH) and malondialdehyde (MDA) were significantly increased, whereas the activity of glutathione peroxidase (GPx) significantly decreased and oxidative stress-related gene significantly changed. Liver lesions were mainly characterized by inflammatory cell infiltration, hepatocyte necrosis and fat vacuolation after exposure to Hg²⁺. Taken together, the results indicate that Hg²⁺ exposure leads to growth inhibition and oxidative stress in juvenile silver.

Reproductive toxicity of environmental levels of triphenyltin to the marine rotifer, Brachionus plicatilis

Triphenyltin (TPT) is a representative organotin often used in marine antifouling coatings, herbicides, and pesticides. However, leaching of TPT into water may be toxic to aquatic life. In this study, environmental concentrations of TPT were used to explore reproductive toxicity of TPT to Brachionus plicatilis, a representative marine rotifer. Toxicity was examined at individual, biochemical, and molecular levels and via phenotypic traits. Rotifers exposed to 10 ng/L TPT group showed increased population size, improved reproductive rate, and a higher weekly growth rate. At 100 ng/L TPT group, the greatest degree of oxidative damage was seen. Exposure to 200 ng/L TPT group shorten generation time, delayed reproduction, and obscured the reproductive peak. Expression of the Vasa gene associated with reproduction was increased after exposure to 10 and 200 ng/L TPT group and decreased at 100 ng/L TPT group. High concentrations of TPT reduced rotifer body length and width and slowed swimming speed. Findings provide a better understanding of the adverse effects of changing TPT concentrations on marine rotifer, by the life cycle parameters, oxidative stress defense mechanisms, expression of a gene related to reproduction, and phenotypic traits. This paper firstly analyzed the reproductive toxicity of environmental levels of organotin compounds to zooplankton, which provided new data support for the comprehensive evaluation of its marine ecological toxicity.

Species-specific effects of iron on temperate and tropical marine rotifers in reproduction, lipid and ROS metabolisms

Two euryhaline rotifers, the temperate species Brachionus plicatilis and tropical species Brachionus rotundiformis, were used to investigate the effects of iron (FeSO4·7H2O), an essential trace metal, on reproductive patterns and lifetables, including the metabolism of lipid and reactive oxygen species (ROS). B. plicatilis was more sensitive to iron with regard to sexual reproduction. While iron had no significant effect on the population growth at 0-48 μg/mL, it caused a decrease in the resting egg production. B. plicatilis exposed to 6 and 12 μg/mL of iron showed an increase in the intracellular ROS levels and a decrease in the neutral lipid content in sexual organs, accompanied by downregulation of antioxidant components CuZnSOD and two cytochromes (CYP clan 2&3). These patterns suggested that iron-induced oxidative stress was not neutralized by its antioxidant defense system, thus negatively affecting the fecundity of fertilized mictic females. However, B. rotundiformis showed a dose-dependent increase in population growth with extended lifespan and positive sexual reproduction in response to 0-24 μg/mL iron. Furthermore, compared to Fe-exposed B. plicatilis, B. rotundiformis showed better antioxidant mechanism, whereas genes involved in lipid synthesis (citrate lyase, mitochondrial CYP) and reproduction (vasa, sirtuin-2) were significantly upregulated compared to the control, implying that B. rotundiformis was likely to have higher resilience in response to iron-induced oxidative stress. These findings suggest that iron is likely to cause interspecific interactions in the B. plicatilis species complex, whereas the tropical species B. rotundiformis may have evolved an effective defense mechanism against iron-induced stress.