Impacts of salinity and fish-exuded kairomone on the survival and macromolecular profile of Daphnia pulex.

Global warming is already causing salinization of freshwater ecosystems located in semi-arid regions, including Turkey. Daphnids, which are important grazers on phytoplankton and a major food source for fish and invertebrates, are sensitive to not only changes in salinity levels, but also presence of predators. In this study, the interactive effect of salinity toxicity (abiotic factor) with predation pressure mimicked by the fish-exuded kairomone (biotic factor) and the effect of salt acclimation on daphnids were investigated. Impacts of these stressors on daphnid survival, life history and molecular profile were observed. The presence of the kairomone antagonistically alters the effect of salinity, as observed from the 24- and 48-h LC(50) values and survival results. Molecular findings provided solid evidence to this antagonism at even lower salt concentrations, for which antagonism was not evident with organismal data. Fish predation counterbalances the negative effect of salinity in terms of reserve energy density. Therefore, it is important to investigate multiple stressor effects in ecotoxicological bioassays complemented with molecular techniques. The single effect of increasing salinity resulted in increased mortality, decreased fecundity, and slower somatic growth in Daphnia, despite their acclimation to salinity. This insignificance of acclimation indicates that Daphnia do not have any physiological mechanisms to buffer the adverse effects of salinity, making it a very crucial factor. Salinity-induced reduction in population growth rate of freshwater keystone species Daphnia-despite acclimation-indicates that global warming-induced salinity may cascade through the food web and lead to dramatic environmental consequences in the structure of lake ecosystems.

Tracking the microplastic accumulation from past to present in the freshwater ecosystems: A case study in Susurluk Basin, Turkey.

Microplastic pollution in aquatic ecosystems has become a global issue in recent years due to its presence everywhere around the world. Although several studies have explored the impact of the accumulation of those small particles in marine environments, comparisons of freshwater systems with marine environments are scarce. In the current study, due to the lack of long-term data on microplastic pollution, we used paleolimnological approaches to acquire the missing information regarding this hot topic. Two short cores were taken from Bursa province in Turkey, which is the center of industrial and agricultural production with many different sectors such as textile and manufacturing. The first core sample was taken from a relatively pristine environment, Lake Uluabat, and the second one was taken from a delta area where all the discharge coming from the basin flowed through to the Marmara Sea. The sediment core from the lake was dated back to the 1960's and the majority of the sample was dominated by fibers. Despite there being no uniform distribution pattern, the number of the microplastics showed decreasing trend after the lake became a Ramsar site. Due to the continuous mixing in the sampling area, there were obstacles via the dating of the Delta core. Nevertheless, the data showed that a high number and variety of microplastics have accumulated over the last decade in the province. This can be interpreted as microplastic pollution reaching the sea directly from the basin. These findings revealed that a plastic chronostratigraphy would give important temporal data regarding the microplastic accumulation in aquatic ecosystems.

Effects of 4-nonylphenol, fish predation and food availability on survival and life history traits of Daphnia magna straus.

This study aimed to investigate the compound effect of environmentally relevant 4-nonylphenol (NP) concentrations and natural stressors-namely fish predation and food availability-on Daphnia magna, which were exposed to four NP concentrations (0, 1, 5 and 10 microg l(-1)) under optimum or low food concentrations (1.00 and 0.075 mg C l(-1), respectively) in water (un)conditioned by a fish predator (Alburnus alburnus). A(n) "environmentally relevant" and "no observable effect" concentration (NOEC) of NP (10 microg l(-1)) resulted in a significant reduction (P < 0.01**) in daphnids' survival when it was encountered concurrently with conditions of low food availability and presence of fish predation. The significance of the results lies in the observation that not only environmentally relevant concentrations of NP but also NP concentrations reported to have no observable effect on daphnids may in reality have unexpected critical effects on D. magna survival under conditions more parallel to natural ecosystems. The deterioration of the life-history traits-namely, NP-induced delay in the age at first reproduction (P < 0.001***) and fish kairomone-induced reduction in the size at first reproduction (P < 0.001***)-of the D. magna individuals is also crucial, as such alterations could significantly influence future generations and result in ultimate adverse effects at the community level because large-bodied daphnids are key-stone species in freshwater ecosystems. The results of this study demonstrate the importance of taking into account environmentally realistic conditions while investigating the effects of NOEC levels of toxicants on non-target aquatic species.

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins.

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.

Food web effects of titanium dioxide nanoparticles in an outdoor freshwater mesocosm experiment.

Over the course of 78 days, nine outdoor mesocosms, each with 1350 L capacity, were situated on a pontoon platform in the middle of a lake and exposed to 0 µg L(-1) TiO2, 25 µg L(-1) TiO2 or 250 µg L(-1) TiO2 nanoparticles in the form of E171 TiO2 human food additive five times a week. Mesocosms were inoculated with sediment, phytoplankton, zooplankton, macroinvertebrates, macrophytes and fish before exposure, ensuring a complete food web. Physicochemical parameters of the water, nutrient concentrations, and biomass of the taxa were monitored. Concentrations of 25 µg L(-1) TiO2 and 250 µg L(-1) TiO2 caused a reduction in available soluble reactive phosphorus in the mesocosms by 15 and 23%, respectively, but not in the amount of total phosphorus. The biomass of Rotifera was significantly reduced by 32 and 57% in the TiO2 25 µg L(-1) and TiO2 250 µg L(-1) treatments, respectively, when compared to the control; however, the biomass of the other monitored groups-Cladocera, Copepoda, phytoplankton, macrophytes, chironomids and fish-remained unaffected. In conclusion, environmentally relevant concentrations of TiO2 nanoparticles may negatively affect certain parameters and taxa of the freshwater lentic aquatic ecosystem. However, these negative effects are not significant enough to affect the overall function of the ecosystem, as there were no cascade effects leading to a major change in its trophic state or primary production.