Invasive Australian swamp stonecrop (Crassula helmsii) negatively affects spawning but accelerates larval growth of the endangered natterjack toad (Epidalea calamita)

C. helmsii often invades the breeding habitat of endangered amphibians, such as Epidalea calamita. However, effects on natterjack population were unclear. The spawning rate, egg survival and the speed of larval growth of this toad species in relation to the presence of C. helmsii were studied. For this study we’ve measured temperature (by temperature data loggers) and chemical properties (by ICP- and AA analysis) of the water, as affected by C. helmsii. Additionally we’ve measured numbers of spawning, egg survival and larval sizes to investigate larval growth rate performing an exclosure experiment at a field location (Gijzenrooise zegge). *The data appropriate to this article may contain Dutch notes. For an English explanation, please contact the author of the data Abstract of the paper: The invasive Crassula helmsii is expanding in Europe. Several ecological effects are described, most of which focus on ecosystem functioning and native vegetation but rarely on fauna. In North-western Europe, C. helmsii often invades the breeding habitat of endangered amphibians, such as Epidalea calamita. The spawning rate, egg survival and the speed of larval growth of this toad species in relation to the presence of C. helmsii were studied. In order to unravel causal mechanisms, the outcome is related to temperature and chemical properties of the water, as affected by C. helmsii. Spawning and egg survival were significantly lower in case of C. helmsii dominance compared to bare soil conditions, and negatively affected the population size of E. calamita. However, larval growth rate was significantly higher in C. helmsii dominated treatments, which could be beneficial for tadpoles. Differences in water temperature and chemistry were a possible explanation for these effects. It remains unclear whether the population viability of E. calamita is negatively affected when C. helmsii is present. In many areas, however, this plant species completely overgrows and causes desiccation of waterbodies. Therefore, appropriate management measures will be required to protect this toad against this invader