Our understanding of aquatic ecology and ecosystem functioning continuously improves. The special issues of Hydrobiologia on "Emerging Trends in Aquatic Ecology" each represent a collection of papers to testify to the variety of approaches and topics that concur in reaching the common aim to scientifically underpin political and societal decisions to mitigate our impacts on our planet and its biodiversity.The series started exactly 100 volumes ago, with volume 750 in 2015 (Martens, 2015). We here proudly present the fourth edition of the series, with papers from colleagues within and outside of the editorial board of the journal.The current trend of continuous biodiversity loss resulted in several international and national regulations and funding schemes to target biodiversity protection and halt its loss. Such a trend is clearly reflected in the papers published in this special issue, which now, more than in the previous editions of the ETAE (Naselli-Flores et al., 2017;Thomaz et al., 2020), present studies that improve our basic understanding of the patterns and processes in biodiversity, that introduce and review state-of-the-art tools and approaches to study biodiversity, that use biodiversity to monitor and assess ecological quality of waters, and that study the effects of anthropogenic activities and climate change on aquatic biodiversity.Three papers deal with the distribution of species. They addressed the influence of abiotic processes like floodings on species occurrence and interactions in plants in the Amazons (da Silva et al., 2023), the role of dried aquatic macrophytes in dispersal of Neotropical ostracods (Rosa et al., 2023), and potential biases affecting our understanding of biodiversity and biogeography of microscopic aquatic organisms (Marrone et al., 2023 provide advice on the use of different literature databases when searching for literature surveys on topics in aquatic ecology, given
