Dear Colleagues,

Phytoplankton is a diverse group of the autotrophic components of the plankton community, which plays a key role in ocean and freshwater ecosystems. It is the base of several aquatic food webs and in a balanced ecosystem provides food for a wide range of organisms. Phytoplankton can vary from prokaryotic cyanobacteria, through plant-like algae, to armor-plated diatoms, dinoflagellates, or marine coccolithophores. These mostly unicellular, seemingly uncomplicated organisms are still a source of new information about their toxicity, prey "hunting" methods, and invasiveness. Crypto-diversity within the species is also an interesting phenomenon.

These organisms inhabit the upper sunlit layer of almost all freshwater bodies and oceans on Earth. Phytoplankton, like terrestrial plants, is exposed to seasonal variation and has markedly faster turnover rates than plants. Hence, phytoplankton responds rapidly on a global scale to natural environmental dynamics and human-made impacts. Moreover, many representatives of phytoplankton, whether single species or even whole genera, are indicatory organisms of changes that occur in fresh and marine waters. These changes mainly manifest in changes in the trophic status of aquatic ecosystems and the ecological state of waters. Especially in this rapidly changing world, natural impacts such as climate change and ocean acidification as well as anthropogenic effects such as fisheries or industrial pollution may result in damages to aquatic food web structure and even phenology, including trophic interactions between phytoplankton, zooplankton, and related communities. Therefore, it is critically important to understand how phytoplankton communities are affected by those impacts in order to take better care of them.

In this Special Issue, we look forward to articles that address phytoplankton biodiversity, both marine and freshwater. We very much welcome papers dealing with changes in phytoplankton as a whole community, but also with individual groups of phytoplankton, as well as papers that demonstrate the connection between the effects of natural and anthropogenic causes on phytoplankton manifesting in the form of changes in the phenotype and genotype of species.

Dr. Małgorzata Poniewozik
Guest Editor

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• anthropogenic impacts
• biodiversity
• climate change
• indicator species
• phenotypic plasticity
• phylogenetic analyses
• phytoplankton
• taxonomy
• temporal and spatial distribution of phytoplankton