Sublethal and lethal effects of pharmaceuticals and agricultural chemicals on the reproduction of freshwater crayfish

"By ecology, we understand the entire science of the organism's relations to the surrounding outside world, which include all "conditions of existence" in a broader sense. These are partly organic, partly inorganic; both are, as we have previously shown, of the greatest importance for the form of organisms, because they force it to adapt to them.” This is the first definition of the term ecology from 1866, written down in the work "Generelle Morphologie der Organismen" (General Morphology of Organisms) by Ernst Haeckel. Even today, more than 150 years later, this definition has not lost its meaning. On the contrary, research has increasingly focused on a holistic biological approach in recent decades. The inclusion of anthropogenic impacts is a growing field of study. In particular, the consideration of negative effects on organisms and, thus, on the entire ecosystem due to chemicals introduced into surface waters has become more and more important. Therefore, this aspect is focused on in this dissertation. In order to expand the understanding of the effects of chemical pollution, this thesis investigates whether and how certain substances affect the reproduction of crayfish, a group that is of particular importance for the ecosystem due to their diet and their impact on the structure of the water body. To this end, the influence of two chemicals on the gonadal maturation and embryonic development of the endangered, native noble crayfish (Astacus astacus) and the non-native parthenogenetically reproducing marbled crayfish (Procambarus virginalis) was investigated in laboratory studies. The substances Diclofenac and Terbuthylazine were selected for this study because of their high incidence in surface water bodies and their known toxicity. Diclofenac is a drug that is used to treat pain and inflammation in both human and veterinary medicine, while Terbuthylazine is a pre-emergence herbicide used primarily in the cultivation of sorghum, citrus fruits, corn, grapes and apples. The results show the impairment of noble crayfish reproduction in all tested concentrations, which were chosen to cover both, actually measured concentrations in surface waters and much higher doses of both substances. Especially sublethal effects such as histopathological changes and size deficits of the offspring occurred. In contrast, marbled crayfish show a higher resistance to the pollutants. While the effects induced by Diclofenac are still comparable to those on noble crayfish, the other results show that the reproduction of marbled crayfish is only impaired at concentrations that are multiple times higher than the amounts of substances that can actually be detected in surface waters. Therefore, the results of the laboratory investigations show that the reproduction and also the population dynamics of noble crayfish are impaired by currently existing substance concentrations in surface waters. In addition, it was shown that the use of marbled crayfish as model organisms for the determination of effective concentrations of individual substances is only possible to a limited extent. Since both substances do not usually occur in the environment as single contaminants but are usually introduced into surface waters together with a number of other chemicals through agricultural drains or outlets of sewage treatment plants, the effects of real mixed contamination were also investigated. For this purpose, egg-carrying female noble crayfish were exposed to different levels of contamination in surface waters in a field study. The pollution, which was discharged through a sewage treatment plant outlet, had immense effects on the embryonic development of the animals. Both lethal and sub-lethal effects could be demonstrated. Overall, this work shows that concentrations of environmental chemicals, currently measured in surface waters of Europe and beyond, influence the reproduction and, thus, the conservation of endangered noble crayfish. As a consequence, the contamination of water bodies should be controlled more closely, and the discharge of chemical substances should be prevented more effectively.