Metabolic responses of freshwater crustaceans to climate change and other anthropogenic stressors

Global biodiversity is nowadays being lost at an accelerated rate, and it is mainly due to human action. Several aspects of human interference have been claimed as particularly threatening for species and ecosystems, but for a long time they have been studied and considered separately. Instead, in recent years, it has emerged that some of these threats can interact, thus causing deeper effects. In my PhD thesis I took into account three of the main anthropogenic stressors to natural environments. In particular I investigated some aspects of the interaction between climate change and other two menaces, invasive species and pollution, focusing my research on freshwater crustaceans. A large part of my work considered the interaction between climate change and a notorious invasive species, non native for European freshwater environments: the red swamp crayfish Procambarus clarkii. This astacid, native of North America, is one of the most cosmopolitan alien crayfish, being introduced in all continents except Australia and Antarctica. It nowadays represents one of the 100 worst invasive species for Europe, causing several problems to invaded ecosystems and human activities. I investigated different aspects of the biology of this species, analyzing how they are influenced by temperature and other environmental factors linked with global warming. I firstly considered the effect of water temperature on its aggressive behaviour during interactions with other invasive crayfish species for Europe. My experiment revealed that this crayfish doesn’t suffer the increase of temperature, remaining highly competitive at temperatures at which other species result weakened. Then I studied some aspects of its physiology, analyzing adults’ thermal tolerance and investigating their ability to exploit aerial environment. This part of my work stressed that adults can bear temperature up to 37 °C and that this wide tolerance is due to their capability to efficiently breathe air. They in fact showed peculiar behaviours which allowed them to use aerial environment both to compensate water hypoxia and to thermoregulate. I also extended the study of thermal tolerance to embryos and early juveniles, being these onthogenetic stages typically more sensitive than adult one. In this part I could figure out that the thermal window of these phases is only slightly narrower than adults’ one, and that ovigerous females can actively select the most suitable temperature for embryos. Since global warming is expected to alter the extent and the salinity of transitional zones, and being my target species recently reported in slightly brackish areas, during my PhD I also worked on the salinity tolerance of P. clarkii. A high level of this parameter (27 ppt) resulted to be limiting for this crayfish. On the other hand P. clarkii revealed to easily sustain salinities up to 9 ppt, bringing us to conclude that this species could extend its spread to water bodies with low salinity levels. Moderately brackish water is not the only atypical habitat, for a freshwater crayfish, in which my study species could extend its threat. Another sensitive environment exposed to risk of invasion is represented by groundwater. During my PhD period, in fact, I reported for the first time the presence of this species in caves outside its native range. My target species has thus revealed to bear different environmental stressors and to possess several adaptations that make it able to face most of the environmental modifications forecasted in climate change scenarios. In addition to the main subject of my PhD, described above, I investigated the interaction between climate change and pollution, in order to analyse the effects of temperature rising and agriculture derived pollutant on alluvial aquifers. I conducted a preliminary experiment in which I measured the metabolic rates of two copepods species: Eucyclops serrulatus, an epigean species commonly found even in groundwater, and the hypogean Diacyclops belgicus that, differently from the previous one, presents several adaptations to groundwater life. My experiment showed a lower metabolic rate for the hypogean species; this feature, probably useful in a low energy environment, could limit the capability of this species to bear thermal and chemical variation. My work in progress will help in clarifying this topic and in forecasting the effects of temperature rising and pollution on this peculiar ecosystem and on the species which inhabit it.