Effects of marine contaminant mixtures on the copepod genus Pseudocalanus. How ambient contaminant mixtures affect mortality, food intake and fecal pellet production.

Abstract: Chemicals are present in almost every part of human society and their benefits to our everyday life are undeniable. Besides those benefits, chemicals are known to cause harm to both human health and the environment. As a consequence of runoff, discharge or leachates, a huge amount of chemicals produced and used will finally be released into the environment. Thus, a broad variety of different chemicals end up in the marine ecosystems, where organisms are exposed to a mixture of compounds. Zooplankton play an important role in marine ecosystems and represent several functions. Being grazers and also grazed upon, zooplankton connect the producers at the base of the food web with consumers at higher trophic levels. Furthermore, zooplankton fuels the biological carbon pump by producing fecal pellets that act as food source deeper in the water column. The most abundant group of zooplankton are copepods. Therefore, understanding impacts of different stressors on copepod species is crucial and a lot of ecotoxicological studies focus on those zooplankton group. The genus Pseudocalanus is among the numerically most dominant copepod genera in several marine ecosystems, including the Swedish and Norwegian west coast. The focus of this study was to determine changes of the copepod genus Pseudocalanus and to understand how marine contaminant mixtures from the west coast of Sweden affect those organisms. Six chemical extracts derived from water samples at six locations around Stenungsund were used. The municipality Stenungsund and the surrounding area contains agriculture, industry, harbours and hosts both thousands of inhabitants and tourists, which represents a wide variety of potential chemical sources and pathways for those compounds to reach the marine environment. Even though the predicted toxicity of the six chemical extracts containing polar organic compounds did not raise any concern, the experimental approach was set-up to prove the theoretical calculations. The results of this study are both unexpected and worrying. Significant increase in mortality was detected in concentrations five times higher than ambient environmental conditions (5x MEC). Furthermore, food intake and fecal pellet production were significantly reduced, down to approximately 20 % and 40 % in the 5x MEC form site M6 and even the ambient environmental concentration (1x MEC) indicated reduction (Figure 13 A, B). Both replicability and reliability of those results were proven, and I therefore suggest further research on different copepod species, younger life stages and additional endpoints. My results raise concern, especially when considering that the chemicals the copepods were exposed to, do not represent the entire ambient contaminant situation. Compounds like heavy metals and nonpolar organic compounds were not sampled, which results in an underestimation of my findings. I therefore suggest further investigations in this and other related locations as well as improved sampling techniques which represent the entire environmental contaminant mixture to ensure a clear reflection of the environmental situation and to avoid underestimation of effects.