Phytoplankton plays a key role in marine biogeochemical cycles. Physiological adaptations of phytoplankton affect biodiversity, dynamics and interactions in marine ecosystem networks. Our earlier results indicate a wide range of ecophysiological adaptations that are unconstrained and differentiated at species/lineage level. Physiological adaptations determine the spatial-temporal dynamics in phytoplankton but also resilience of the community to environmental changes. The main objective of this project is a detailed investigation of marine phytoplankton dynamics through its yearly cycles by following composition and physiological characteristics of the community. Next to classical approaches of taxonomic identification and physiology measurements, we will implement high-throughput molecular methods based on next generation sequencing of barcodes and transpcritomes. To better understand physiological responses of phytoplankton species and improve taxonomic resolution of metatranscriptome analyses, this project will isolate key species from environmental samples are isolated in into monoclonal cultures and subject them to nutrient limitations. This approach will result in a valuable dataset of physiological responses (transcriptome reference database and resource responsive gene expression) of targeted (key) species to targeted (key) conditions. The Northern Adriatic offers marked ecological gradients and represents an ideal ecosystem to observe phytoplankton/transcriptomes under different ecological challenges. Inclusion of the South Adriatic will gieve a wider aspect and allows comparisons between two connected but diverse environments. The expected results will allow this project to test and characterize the hypothesized niche compartmentalization in plankton ecology. This project further will allow a deeper understanding of the physiological pathways and adaptations of phytoplankton and will furthermore shed light on the complex life strategies of key species.