The Effects of Petroleum Hydrocarbons on Algae Can Be Reversed in the Presence of a Primary Consumer

The toxic effects of petroleum pollutants to microalgae in marine environment

Marine oil pollution is one of the major global environmental pollution problems. Marine microalgae are the foundation of the marine food chain, providing the main primary productivity of the ocean. They not only maintain the energy flow and material cycle of the entire marine ecosystem, but also play an important role in regulating global climate change. Exploring the impact of petroleum pollutants on marine microalgae is extremely important for studying marine environmental pollution. This review first introduced the sources, compositions, and forms of petroleum pollutants and their migration and transformation processes in the ocean. Then, the toxic effects of petroleum pollutants on marine microalgae were summarized. The growth of marine microalgae showed low-concentration promotion and high-concentration inhibition. The population growth and interspecific relationships of marine microalga was changed and the photosynthesis of marine microalgae was influenced. Finally, potential research directions and suggestions for marine microalgae in the future were proposed.

Periodic density as an endpoint of customized plankton community responses to petroleum hydrocarbons: A level of toxic effect should be matched with a suitable time scale

As an endpoint of community response to contaminants, average periodic density of populations (APDP) has been introduced to model species interactions in a community with 4 planktonic species. An ecological model for the community was developed by means of interspecific relationship including competition and predation to calculate the APDP. As a case study, we reported here the ecotoxicological effects of petroleum hydrocarbons (PHC) collected from Bohai oil field on densities of two algae, Platymonas subcordiformis and Isochrysis galbana, a rotifer, Brachionus plicatilis, and of a cladocera, Penilia avirostris, in single species and a microcosm experiment. Time scales expressing toxic effect increased with increasing levels of toxic effect from molecule to community. Remarkable periodic changes in densities were found during the tests in microcosm experiment, revealing a strong species reaction. The minimum time scale characterizing toxic effect at a community level should be the common cycle of population densities of the microcosm. In addition, the cycles of plankton densities shortened in general with increasing PHC, showing an evident toxic effect on the microcosm. Using APDP as the endpoint, a threshold concentration for the modeled microcosm was calculated to be 0.404 mg-PHC L^-1. The APDP was found to be more sensitive and reliable than the standing crops of populations as the endpoint. This indicated that the APDP, an endpoint at the community level, could be quantitatively related to the endpoints at the population level, and led to the quantitative concentration-toxic effect relationship at the community level.

A toxic effect at molecular level can be expressed at community level: A case study on toxic hierarchy

This study demonstrated hierarchical toxicity and addressed the relevance and differences of toxic effects at the molecular, individual, population, and community levels. Superoxide dismutase (SOD) activity, photosynthetic oxygen production, filtration rate, life span and densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized community tests were examined in response to a concentration gradient of aniline ranging from 0 to 50.0 mg L^-1. The SOD activity was the most sensitive endpoint with the fastest response to aniline according to the calculated no-detection of toxic effect concentration (NDEC) and the EC₅₀. The individual- and population-level endpoints, showing a lower response to aniline, could be constructed from the SOD activity in a stepwise manner. A multi-scale hierarchical model with endpoints at 4 levels was used to characterize toxic effects, at the scales of time and size. Linkage of SOD activity to toxic effects at a community level was established level by level to express the change in the customized community with the concentration of aniline. The calculated threshold concentration of aniline for the customized community was nearly equal to the minimum NDEC, demonstrating as great an impact on interactions by the toxic effect at subpopulation-level as that at the community level. However, we identified a trend of higher sensitivities of measured endpoints at sub-population level, decreasing sensitivity at higher levels but a great variety of sensitivities at community level. Although the characteristics of toxic effects are different at different levels, the structure and process of endpoints at adjacent levels are related to and interact with each other. The resulted indirect effects, together with direct effect, determine the toxic effect at every levels of biological complexity. The toxic effects at adjacent levels should be studied at the same time to better understand the ecological risk of contaminants.

The ecological competition and grazing reverse the effects of sulfamethoxazole on plankton: a case study on characterizing community-level effect

The toxic effects of sulfamethoxazole (SMX) on densities of two algae, Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and of a rotifer, Brachionus plicatilis, were tested by the population and community experiments. Two endpoints, the carrying capacity and the densities array of community in steady state (DACS), were used to characterize the toxic effects at a population level and a community one, respectively. The results showed that the carrying capacity of P. helgolandica var. tsingtaoensis and B. plicatilis did not decline significantly in population test when the concentration of SMX was lower than 6.0 mg L^-1 and 12.0 mg L^-1, respectively. However, I. galbana was sensitive to SMX and had presented toxic effect at 3.0 mg L^-1. By extrapolation of toxic effect at a population level to a community one, a derived community-NOEC was 3.0 mg L^-1, representing an inference from data of toxic effects at population level. In community experiment, when the customized community was in steady state, the density of I. galbana increased as a whole with SMX concentration in the range of tested concentration (0-144 mg L^-1), while that of P. helgolandica var. tsingtaoensis assumed the trend of a reversed "v" in this range. Only the density of B. plicatilis decreased with SMX concentration. With the DACS as endpoint, a NOEC for the customized community was determined to be 6.0 mg L^-1. This indicates that interspecific interactions can reverse the toxic effects of SMX on phytoplankton. The DACS was reliable and stable, serving as the endpoints in assessment of the effects of the pollutants on the ecosystems.

Interspecies Interactions Reverse the Hazard of Antibiotics Exposure: A Plankton Community Study on Responses to Ciprofloxacin hydrochloride

The ecotoxicological effects of Ciprofloxacin hydrochloride (CIP) were tested on population densities of plankton assemblages consisting of two algae (Isochrysis galbana and Platymonas subcordiformis) and a rotifer (Brachionus plicatilis). The I. galbana showed a significant decrease in densities when concentrations of CIP were above 2.0 mg L⁻¹ in single-species tests, while P. subcordiformis and B. plicatilis were stable in densities when CIP were less than10.0 mg L⁻¹. The equilibrium densities of I. galbana in community test increased with CIP concentrations after falling to a trough at 5.0 mg L⁻¹, showed a completely different pattern of P. subcordiformis which decreased with CIP concentrations after reaching a peak at 30.0 mg L⁻¹. The observed beneficial effect was a result of interspecies interactions of trophic cascade that buffered for more severe direct effects of toxicants. The community test-based NOEC of CIP (2.0 mg L⁻¹), embodying the indirect effects, was different from the extrapolated one derived by single-species tests (0.5 mg L⁻¹), but all lacked confidence interval. A CIP threshold concentration of obvious relevance to ecological interaction was calculated with a simplified plankton ecological model, achieving a value of 1.26 mg L⁻¹ with a 95% bootstrapping confidence interval from 1.18 to 1.31 mg L⁻¹.

Species Composition, Seasonal Dynamics and Distribution of Phytoplankton of the Zaporizke Reservoir

Species composition, seasonal dynamics and distribution of phytoplankton were researched to characterize temporal dynamics and horizontal distribution of phytoplankton and to indicate the ecological status of the sites in the Zaporizke reservoir. During 2015 - 2016 a seasonal dynamics of species composition and quantitative characteristics of phytoplankton have been studied near Monastyrsky island in upper part of the reservoir both in surface and bottom layers in conjunction with water temperature measurement. At early September 2016 phytoplankton sampling was performed at different sites of the Zaporizke reservoir including the sites undergone to sewage impact. During phytoplankton seasonal dynamics diatom bloom was reported in March and early April and algae biomass was higher in the bottom layer with a gradual decrease in the direction of the surface layer. From July to October the apparent dominance of blue-green algae took place with a clear concentration in the surface layer. Domination of the species Microcystis aeruginosa determined phytoplankton distribution along the reservoir at the beginning of September. Despite the high resistance to the effects of toxic substances the level of Microcystis aeruginosa (Kützing) Kützing 1846 development decreased at the sites of direct sewage impact. At 100m below the sewages sites degree of phytoplankton development increased mainly due to increase of blue-green algae abundance. Indexes of phytoplankton showed the best ecological state at the site «near Kodaki water draw-off» and the worst ecological state at the sites of direct sewage impact. The results obtained are important to indicate ecological state of the sites in the Zaporizke reservoir.

Species Composition, Seasonal Dynamics and Distribution of Phytoplankton of the Zaporizke Reservoir

Species composition, seasonal dynamics and distribution of phytoplankton were researched to characterize temporal dynamics and horizontal distribution of phytoplankton and to indicate the ecological status of the sites in the Zaporizke reservoir. During 2015 - 2016 a seasonal dynamics of species composition and quantitative characteristics of phytoplankton have been studied near Monastyrsky island in upper part of the reservoir both in surface and bottom layers in conjunction with water temperature measurement. At early September 2016 phytoplankton sampling was performed at different sites of the Zaporizke reservoir including the sites undergone to sewage impact. During phytoplankton seasonal dynamics diatom bloom was reported in March and early April and algae biomass was higher in the bottom layer with a gradual decrease in the direction of the surface layer. From July to October the apparent dominance of blue-green algae took place with a clear concentration in the surface layer. Domination of the speciesMicrocystis aeruginosadetermined phytoplankton distribution along the reservoir at the beginning of September. Despite the high resistance to the effects of toxic substances the level ofMicrocystis aeruginosa (Kützing) Kützing 1846development decreased at the sites of direct sewage impact. At 100m below the sewages sites degree of phytoplankton development increased mainly due to increase of blue-green algae abundance. Indexes of phytoplankton showed the best ecological state at the site «near Kodaki water draw-off» and the worst ecological state at the sites of direct sewage impact. The results obtained are important to indicate ecological state of the sites in the Zaporizke reservoir.

A method linking the toxic effects at community-level with contaminant concentrations

In this study, we developed a method to quantify and link the toxic effects in community-level ecosystems with concentrations of petroleum hydrocarbons. The densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized ecosystems were examined in response to a concentration gradient of petroleum hydrocarbons ranging from 0 to 8.0mgL(-1). A three-population ecological model with interspecies competition-grazing relationships was used to characterize population sizes with concentrations of petroleum hydrocarbons. A threshold concentration of the simplified plankton ecosystem of 0.376mgL(-1) for petroleum hydrocarbons was calculated from the proposed model, which was higher than the no-effect concentration of 0.056mgL(-1) derived from the single-species toxicity tests and the predicted no-effect concentration of 0.076mgL(-1) calculated from the species sensitivity distribution. This finding indicates that interspecies competition and grazing reduced the toxic effect of petroleum hydrocarbons at the community level. The sensitivity analysis for model parameters demonstrates that plankton population biomasses are highly sensitive to filtration rates. Antagonism between interspecies interactions and petroleum hydrocarbon toxicity was attributed to the reduced filtration rate and zooplankton grazing pressure. The proposed method is a simple means to address the concern regarding the impacts of ecological interactions on ecological risk assessments of pollutants.