Synergistic and additive effects of microplastic, nickel and pyrene on survival, reproduction, and egestion of a tropical copepod.

Coastal tropical ecosystems provide livelihood for millions of people but are at the same time exposed to an increasing intensity of diverse anthropogenic stressors, including pollution. Nevertheless, the combined effects of pollutants on marine ecosystems are poorly understood, particularly regarding lower trophic levels (plankton) and tropical ocean. We exposed the tropical copepod Centropages velificatus to 4-5 concentrations of a heavy metal (nickel), an oil compound (pyrene) and microplastic (PET), either alone or in combination, and measured their egestion, reproduction, and mortality rates. Microplastic alone did not have any effect on pellet or egg production of copepods, whereas nickel reduced egg production rate at concentrations ≥1 µg L-1 and pyrene reduced both egg and pellet production rates at concentrations ≥1 nM. The addition of nickel and pyrene to PET - microplastic resulted in a reduction similar to one caused by nickel or pyrene alone, suggesting an additive effect. In contrast, a combination of nickel and pyrene had a synergistic effect, with a strong reduction in survival, egg and pellet production. Our results suggest that combinations of contaminants that are commonly found in tropical coastal waters have detrimental effects on copepods-the crucial link in the pelagic food web-at lower concentrations than suggested by single stressor studies. This can have an influence on the food web productivity - the basis of fisheries that local communities rely on.

Microbial bioremediation of produced water under different redox conditions in marine sediments.

The discharge of produced water from offshore oil platforms is an emerging concern due to its potential adverse effects on marine ecosystems. In this study, we investigated the feasibility and capability of using marine sediments for the bioremediation of produced water. We utilized a combination of porewater and solid phase analysis in a series of sediment batch incubations amended with produced water and synthetic produced water to determine the biodegradation of hydrocarbons under different redox conditions. Significant removal of benzene, toluene, ethylbenzene and xylene (BTEX) compounds was observed under different redox conditions, with biodegradation efficiencies of 93-97% in oxic incubations and 45-93% in anoxic incubations with nitrate, iron oxide or sulfate as the electron acceptor. Higher biodegradation rates of BTEX were obtained by incubations dominated by nitrate reduction (104-149 nmolC/cm3/d) and oxygen respiration (52-57 nmolC/cm3/d), followed by sulfate reduction (14-76 nmolC/cm3/d) and iron reduction (29-39 nmolC/cm3/d). Chemical fingerprint analysis showed that hydrocarbons were biodegraded to smaller alcohols/acids under oxic conditions compared to anoxic conditions with nitrate, indicating that the presence of oxygen facilitated a more complete biodegradation process. Toxicity of treated produced water to the marine copepod Acartia tonsa was reduced by half after sediment incubations with oxygen and nitrate. Our study emphasizes the possibility to use marine sediment as a biofilter for treating produced water at sea without extending the oil and gas platform or implementing a large-scale construction.

Climate change and oil pollution: A dangerous cocktail for tropical zooplankton.

Climate change and oil pollution pose a major threat to tropical marine ecosystems and to the coastal communities relying on their resources. The Gulf of Guinea is severely affected by multiple human induced stressors, but the potential impacts of these on marine productivity remain unknown. We investigated the combined effects of heatwaves (climate stressor) and the polycyclic aromatic hydrocarbon pyrene (proxy for oil) on the copepod Centropages velificatus. We quantified survival, reproduction and fecal pellet production of females exposed to concentrations of 0, 10, 100 and 100+ nM (saturated) pyrene under simulated heatwaves of different thermal intensity (+3 °C and +5 °C above control treatment temperature). Thermal stress due to both moderate and intensive heatwaves resulted in reduced survival and egg production. The negative effects of pyrene were only measurable at the high pyrene concentrations. However, thermal stress increased the sensitivity of C. velificatus to pyrene, indicating a synergistic interaction between the two stressors. We document that the interaction of multiple stressors can result in cumulative impacts that are stronger than expected based on single stressor studies. Further research is urgently needed to evaluate the combined impact of climatic and anthropogenic stressors on the productivity of coastal ecosystems, particularly in the tropical areas.