The e!ects of the invasive Australian swamp stonecrop on the natterjack toad - A fight between two pioneer species In Dutch nature reserves there is a growing problem of the invasive species Australian swamp stonecrop (Crassula helmsii). This species often forms a thick biomass layer in freshwater systems, where it outcompetes native species and negatively influences water quality. The invasive species thrives on bare soils, both semi terrestrial and aquatic, which also provide habitat for the in the Netherlands native and endangered pioneer species: the natterjack toad (Epidalea calamita). In this research we test if Australian swamp stone crop negatively influences the deposition and hatching rate of natterjack toads eggs and the larvae growth and survival rate. We found that Australian swamp stonecrop significantly reduces natterjack toad egg deposition and hatching, threatening the reproduction and thereby the existence of the natterjack toad in areas with the invasive species. On the contrary, the presence of Australian swamp stonecrop unexpectedly increases larvae growth speed. Consequently, the larvae in presence of the invasive species reached the metamorphosis stage at a larger size than the larvae in the absence of Australian swamp stonecrop. Whether this is beneficial for these natterjack toads is unclear. This might be caused by the more stable and on average lower water temperatures in the presence of the invasive species and/or higher food availability. We conclude that the negative e!ects of Australian swamp stonecrop on the natterjack toad larvae ask for a response in which the invasive species is controlled and reduced in biomass and distribution. Het Brabants Landschap werkt in het natuurgebied de Gijzenrooise Zegge aan natuurherstel, met als speerpunt de ontwikkeling van de aanwezige populatie van rugstreeppad. Bij de ontwikkeling van het gebied raakten de kale waterbodems in een nieuw gegraven water al snel begroeid door watercrassula, een invasieve exoot afkomstig uit Australië. In opdracht van de provincie Noord-Brabant werden door Stichting Bargerveen en Soontiëns Ecology de e!ecten op de voortplanting van rugstreeppadden onderzocht.

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L. van Veenhuisen, J. van der Loop, M. van de Loo, & H. van Kleef. (2021). De effecten van watercrassula op rugstreeppad- Een gevecht tussen pioniers. RAVON, 23(1), 5–8.
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