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.

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.

Biochemical characteristics of zooplankton entering Atlantic mackerel processing plants in Iceland as side-catch.

The Northeast Atlantic mackerel (Scomber scombrus) is a zooplanktivorous fish with its main summer feeding grounds in the waters around Iceland. The zooplankton in the stomachs of the caught fish causes several problems during processing due to the high enzyme activity of the zooplankton. The aim of the study was to evaluate the chemical characteristics of zooplankton that accompanies mackerel as a side-catch and stomach fullness as affected by catching year, season, catching zone, and catching method over three mackerel seasons from 2016 to 2018. Species identification by the fatty acid tropic marker method (FATM) was also applied within the zooplankton rich side-stream. FATM analysis indicated that the majority of the zooplankton mass belonged to Calanus finmarchicus. The lipid composition of the zooplankton rich side-stream varied between years but was rich in monounsaturated, as well as polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The results suggest that the zooplankton rich side-stream from mackerel caught in Icelandic waters has the potential for further sustainable processing into valuable nutrients.