Phytoplankton and anthropogenic changes in pelagic environments

“Phytoplankton” is a loosely defined functional term, indicating a group of organisms distributed into several taxonomic groups ranging from oxygenic photosynthetic bacteria to a number of eukaryotic classes included in protists. The range of specializations and adaptations of phytoplankton to a wide variety of environmental conditions is astounding. This demonstrates the susceptibility of highly different populations to react rapidly to environmental changes generated by natural stressors and anthropogenic impacts. The aim of this work is to critically review the state of the art of knowledge about the impact of anthropogenic stress factors on phytoplankton composition and structure. At present, the two most important environmental stressors are represented by climate change and eutrophication, which act globally and at regional/local scales, respectively. Along with effects mediated by many other legacy and emerging stressors (briefly reviewed), the effects of these two main changes have been analysed at different levels of phytoplankton organization, i.e. individuals, populations and communities. It is stressed that a better knowledge will be obtained by extending the focus of studies from organisms detectable by light microscopy to the whole range of protists and microbial populations detected with the use of “omics” technologies, including e.g. next generation sequencing and ecological metabolomics.