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.

Concentration of mercury and other metals in an Arctic planktonic food web under a climate warming scenario.

Arctic marine ecosystems act as a global sink of mercury (Hg) and other metals, and high concentrations of these have been measured in higher trophic-level organisms. Nevertheless, the concentrations of metals at the basis of the marine food web in the Arctic is less known despite the likelihood of biomagnification from dietary sources. We investigated the concentrations of mercury (Hg) and other metals in different size fractions of plankton in West Greenland. All size fractions contained detectable levels of Hg (ranging from 4.8 to 241.3 ng g dw-1) at all stations, although with high geographic variability, likely reflecting the sources of mercury (e.g., meltwater). In many cases, the concentrations in the larger-size fractions were lower than in the smaller-size fractions, suggesting depuration through the metabolic activity of mesozooplankton. Concentrations of Cd, Pb, V, Ni, and Cr were higher than previously reported elsewhere in the Arctic.

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.