In order to understand of the processes controlling phytoplankton successions in the NE Black Sea, long-term data series are needed. We compiled 15 years (2002-2017) of measurements from which the existence emerges of a tight link between phytoplankton species dominance and nutrients concentrations. The latter is strongly influenced by wind direction. The link between algal dominance and nutrients is mediated by the growth strategy adopted by algal species. In spring, when nutrients are abundant, small diatoms such as Pseudo-nitzschia pseudodelicatissima, with a "rapid growth strategy", prevail. In late spring and early summer, when N is low and P and Si are high, coccolithophorids such as Emiliania huxhleyi dominate, thanks to an "affinity growth strategy". Large diatoms, especially Pseudosolenia calcar-avis, dominate in summer and autumn, when their "storage growth strategy" allows the exploitation of discontinuous upwelling of nutrients. These seasonal changes of dominant species influence the structure of the food web.

Laboratorio di Fisiologia delle Alghe e delle Piante Dipartimento di Scienze della Vita e dell'Ambiente Università Politecnica delle Marche Ancona Italy; STU UNIVPM Joint Algal Research Center Shantou China; Institute of Microbiology Academy of Sciences of the Czech Republic Algatech Trebon Czech Republic; National Research Council Institute of Marine Science ISMAR Venezia Italy

P P Shirshov Institute of Oceanology RAS Nakhimovski av Moscow Russia

The Southern Branch of the P P Shirshov Institute of Oceanology RAS Gelendzhik Krasnodar region Russia

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