ABSTRACT The northern Adriatic is a highly dynamic marine ecosystem where multiple environmental stressors, particularly phosphorus limitation, shape phytoplankton communities. Previous studies have established annual phytoplankton succession patterns primarily using light microscopy, while metatranscriptomic analyses have been lacking. This study used a metatranscriptomic approach to investigate the taxonomic and functional dynamics of the northern Adriatic phytoplankton community, focusing on the predominant group of dinoflagellates. Monthly sampling from April 2021 to March 2022 at two coastal stations revealed dinoflagellates as the most metabolically active phylum throughout the year in the size fraction > 50 μm. Peaks in metabolic activity of other studied phyla aligned with the characteristic seasonal species succession observed in previous studies. Community ordination indicated distinct seasonal shifts driven by environmental factors, notably phosphorus and silicon availability, as well as species interactions. Both photosynthesis and phagotrophy emerged as important trophic strategies for dinoflagellates. Nitrogen and phosphorus metabolism showed clear seasonal trends, with dinoflagellates employing various strategies for nutrient acquisition and recycling depending on resource availability. Changes in the activation of different cellular processes highlighted a seasonal shift in metabolic investment, with spring favouring rapid population expansion, while the rest of the year was characterised by prevalent transcription of genes indicative of cellular maintenance and adaptation. This study provides critical new insights into dinoflagellate phytoplankton ecology and emphasises the need for further multi‐method research to fully understand their role in the northern Adriatic ecosystem.
Knjaz et al. (Thu,) studied this question.