Abstract
Data from five sites of the International Long Term Ecological Research (ILTER) network in the North-Eastern Pacific, Western Arctic Ocean, Northern Baltic Sea, South-Eastern North Sea and in the Western Mediterranean Sea were analyzed by dynamic factor analysis (DFA) to trace common multi-year trends in abundance and composition of phytoplankton, benthic fauna and temperate reef fish. Multiannual trends were related to climate and environmental variables to study interactions. Two common trends in biological responses were detected, with temperature and climate indices as explanatory variables in four of the five LTER sites considered. Only one trend was observed at the fifth site, the Northern Baltic Sea, where no explanatory variables were identified. Our findings revealed quasi-synchronous biological shifts in the different marine ecosystems coincident with the 2000 climatic regime shift and provided evidence on a possible further biological shift around 2010. The observed biological modifications were coupled with abrupt or continuous increase in sea water and air temperature confirming the key-role of temperature in structuring marine communities.
Highlights
Long-term ecological research aiming at understanding sources of natural variability in species composition, dominant species and functional diversity of marine communities is essential for disentangling the effects of natural environmental drivers and climate variation from the direct effects of local human activities (Giron-Nava et al 2017; Mirtl et al 2018)
LTER Santa Barbara Channel: Sixteen dynamic factor models were calculated to estimate the underlying common trend of the fish time-series differing in the covariance matrix employed, the number of trends and the included explanatory variables
The Akaike’s information criterion (AIC) values indicated that the best model fit was obtained for a non-diagonal matrix with two common trends explained by bottom temperature and the Pacific Decadal Oscillation (PDO) index (AIC = 415) (Table 2)
Summary
Long-term ecological research aiming at understanding sources of natural variability in species composition, dominant species and functional diversity of marine communities is essential for disentangling the effects of natural environmental drivers and climate variation from the direct effects of local human activities (Giron-Nava et al 2017; Mirtl et al 2018). Of particular note was the 1988 BRS, which was detected in marine ecosystems globally (e.g., Reid et al 2016; Conversi et al 2010), while the 2000 CRS/BRS has been subject to only a few long-term studies in specific marine systems (Kröncke et al 2013a; Beaugrand et al 2014; Dippner and Kröncke 2015; Perretti et al 2017) All these studies have shown that signals of climate variability can be detected by an increase in warm-temperate species, a decrease in cold-temperate species at various trophic levels of the marine ecosystem, and subsequently in changes in species composition and species richness
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