AUTHOR=Vlašiček Ivan , Marić Pfannkuchen Daniela , Smodlaka Tanković Mirta , Baričević Ana , Kužat Nataša , Knjaz Mia , Grižančić Lana , Podolšak Ivan , Kogovšek Tjaša , Pfannkuchen Martin 

TITLE=Cluster analysis of long-term phytoplankton data from the Northern Adriatic reveals environmental influences and disruptions in seasonal patterns

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=Volume 13 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2025.1498307

DOI=10.3389/fevo.2025.1498307

ISSN=2296-701X

ABSTRACT=The Northern Adriatic is a dynamic and the most productive part of the Adriatic Sea. The phytoplankton of the Northern Adriatic is, as many studies in this area showed, under heavy influence of freshwater inputs and anthropogenic pressures. Cluster analysis of a more than 20 year phytoplankton data set across steep spatio-temporal, ecological gradients on a longitudinal transect across the northern Adriatic, allowed us to identify significant and reoccurring phytoplankton species assemblages. Those phytoplankton clusters show stable seasonality and relation to environmental conditions and are presumed to be cornerstones of important ecosystem services provided by phytoplankton. Our results demonstrate that the stable seasonality of important phytoplankton clusters is disrupted, leading to a destabilisation of seasonal patterns in the biodiversity of primary producers. During the last 20 years, clusters characterised by dominating species were replaced by clusters characterised by the coexistence of several species. Overall the frequency of dense blooms of single species appears to decline. Multivariate analysis showed that possible reasons might lie in oligotrophication and increased salinity dynamics. Our results suggest the importance and applicability of cluster analysis in taxon based biodiversity long term data sets to elucidate functional biodiversity changes.