Contents lists available at ScienceDirect Harmful Algae journal homepage: www.elsevier.com/locate/hal Causal relationships of Raphidiopsis (formerly Cylindrospermopsis) dynamics with water temperature and N:P-ratios: A meta-analysis across lakes with diferent climates based on inferential modelling Friedrich Recknagel a, ⁎ , Tamar Zohary b , Jacqueline Rücker c , Philip T. Orr d,1 , Christina Castelo Branco e , Brigitte Nixdorf c a University of Adelaide, School of Biological Sciences, Adelaide, Australia b Israel Oceanographic and Limnological Research, Kinneret Limnological Laboratory, Migdal, Israel c Brandenburg University of Technology, Department of Freshwater Conservation, Bad Saarow, Germany d Seqwater, Brisbane, Australia e Federal University of the State of Rio de Janeiro, Rio de Janeiro, Brazil ARTICLEINFO Keywords: Raphidiopsis raciborskii Meta-analysis Four lakes Climate Eutrophication Hybrid evolutionary algorithm HEA Water temperature N:P-ratios Phenology ABSTRACT Raphidiopsis raciborskii is a tropical toxic cyanobacterium that is rapidly expanding to diverse lake habitats in diferent climate zones by sophisticated adaptation mechanisms. This meta-analysis investigated correlations of R. raciborskii with water temperature and N:P (nitrogen to phosphorus)-ratios across four lakes with diferent climates and trophic states by means of long-term time series and the hybrid evolutionary algorithm HEA. The results have shown that in the lakes with temperate and Mediterranean climate, R. raciborskii is strongly correlated with water temperature since germination and growth rely on rising water temperatures in spring. In contrast, there was a weaker correlation with water temperature in subtropical and tropical lakes where pelagic populations of R.raciborskii are overwintering, and are present all year round. However, the highest abundances of R. raciborskii coincided with highest water temperature for the Mediterranean, subtropical and tropical lakes, whilst in the temperate Langer See the highest abundances of R.raciborskii occurred at 24.1 °C, even though temperatures of up to 27 °C were recorded in 2013 and 2014. The correlation of R.raciborskii with N:P-ratios proved to be strongest for the meso- to eutrophic Lake Kinneret (r 2 = 0.8) and lowest for the eutrophic Lake Paranoa (r 2 = 0.16). However, the assumption has been confrmed that R.raciborskii is growing fastest when waters are N-limited regardless of trophic states. In terms of phenology, the temperate and Mediterranean lakes displayed “fastest growth” in spring and early summer. In contrast, the growing season in subtropical and tropical lakes lasted from spring to autumn most likely because of overwintering populations, and growing importance of direct and indirect biotic regulating factors such as competition, grazing, remineralisation of nutrients along warming climate. In order to carry out a meta-analysis of time series across four diferent lakes, HEA served as powerful tool resulting in inferential models with predictive capacity for population dynamics of R. raciborskii just driven by water temperature or N:P-ratios, whilst coefcients of determination r 2 served as criteria for hypotheses testing. 1. Introduction The expanding global distribution of Raphidiopsis raciborskii (Wołoszyńska) Aguilera, Berrendero Gómez, Kastovsky, Echenique & Salerno (Aguilera et al., 2018) is attributed to a suite of sophisticated adaptation mechanisms characteristic of this bloom-forming nostoca- lean cyanobacterium. Akinetes that germinate only when water temperatures exceed 15 °C enable R. raciborskii to survive the cold months in temperate waters (Padisak, 1997; Rücker et al., 2009). In terms of nitrogen consumption, R. raciborskii shows a preference for dissolved inorganic (ammonium, nitrate) and organic (urea) forms of nitrogen (e.g. Saker and Neilan, 2001; Ammar et al., 2014; Burford et al., 2018), whilst heterocyte cells allow R. raciborskii to grow in N- limited waters by performing N 2 -fxation (e.g. Plominsky et al., 2013). https://doi.org/10.1016/j.hal.2019.04.005 Received 30 October 2018; Received in revised form 10 April 2019; Accepted 10 April 2019 ⁎ Corresponding author. E-mail address: friedrich.recknagel@adelaide.edu.au (F. Recknagel). 1 Present address: Grifth University, Australian Rivers Institute, Nathan, Australia. Harmful Algae 84 (2019) 222–232 1568-9883/ © 2019 Elsevier B.V. All rights reserved. T