| Summary: | This paper aims to reveal current changes (recent decades) in regional climatic variables like water temperature (WT), the duration of the ice-free period (ICE-FREE) and the precipitation rate (P), as exemplified by Petrozavodsk Bay (Lake Onega, European Russia), and to analyse their relationships with the global climatic indices NAO, AO and structural characteristics of biota (chlorophyll a concentration (Chl a), phytoplankton and zoobenthos abundance/biomass) in the lake ecosystem, which lies within the Baltic Sea catchment area. Spearman’s rank correlations yielded significant (p<0.05) relationships between the NAO and planktonic Cyanobacteria abundance, and also between NAO, AO, WT, P and the abundance and biomass of zoobenthos. Chl a correlates positively (R=0.66; p=0.03) with WT and negatively with ICE-FREE (R=−0.53; p=0.05). At the same time, multiple regression analysis confirmed that the global climate governs primarily the regional climatic variables and productivity level in the lake’s ecosystem, whereas most of the biotic characteristics respond to variability in the regional climate.
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