Seasonal phytoplankton dynamics in the coastal waters of the north-eastern Adriatic Sea

This study describes the dynamics of phytoplankton in relation to environmental factors in coastal waters of the north-eastern Adriatic Sea. The distant Po River's influence is rarely noted on the eastern coastal part of the northern Adriatic, but it does trigger the crucial alternations in the community, e.g. mass development of diatoms in July 2009. A highly variable ecosystem, like the northern Adriatic, sustains high species diversity. Even though quite a few species were present for more than several months, we identified the seminal species of the seasonal succession. During spring Prorocentrum micans, Leptocylindrus minimus, Chaetoceros throndsenii, Ceratium furca and Ceratium fusus were most characteristic. These species thrive in low salinity and mixed waters. Typical summer diatom species were Chaetoceros vixvisibilis and Proboscia alata, while Rhabdosphaera clavigera and Syracosphaera pulchra were identified as distinctive summer coccolithophorids. All the summer species preferred warmer waters with low nitrate and low silica content. The autumn community was characterised by species such as Calciosolenia murrayi, Chaetoceros socialis, Asterionellopsis glacialis, and Lioloma pacificum. These species were related not only to high nutrient conditions, but also to low Po River influence. In winter a prevalence of large diatoms Thalassiosira rotula, Neocalyptrella robusta and Pseudosolenia calcar-avis was recorded. The winter assemblage was characterised by species of cold water preference able to grow in well mixed conditions.

► Two year study of phytoplankton community in coastal NE Adriatic ► Importance of diatoms in N Adriatic phytoplankton is confirmed. ► Istrian coast, NE Adriatic, can be influenced by the Po River under stable conditions. ► Succession pattern of species in the coastal area is revealed.