Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 561 (2016): 189-201, doi:10.3354/meps11915. ; Thalia democratica blooms are a recurrent phenomenon in many coastal areas of the Mediterranean Sea and have significant ecological effects. To better understand the environmental drivers of salp blooms, we conducted 8 surveys to sample T. democratica in contrasting seasonal, temperature and chlorophyll conditions. In each survey, short-term variations in the abundances of different salp stages were assessed by sampling the same population at 30 min intervals. Using these data, we estimated the parameters in a set of stage-classified matrix population models representing different assumptions about the influence of temperature and chlorophyll on each stage. In the model that best explains our observations, only females are affected by changes in water temperature. Whether this is a direct influence of temperature or an indirect effect reflecting low food availability, female reproduction cessation seems to slow population growth under unfavourable conditions. When conditions become favourable again, females liberate the embryo and change sex to male, allowing for mating under extremely low salp densities and triggering the bloom. In contrast to previous findings, our results suggest that females, rather than oozooids, are responsible for the sustainability of salp populations during latency periods. ; This work was founded by the Ministerio de Ciencia e Innovación under the Fishjelly project, the European commission ENPI CBC MED project under the Jellyrisk project and the European LIFE Commission under the Cubomed project. M. G. Neubert acknowledges the support of the US National Science Foundation (DEB-1145017 and DEB-1257545). ; 2017-12-15