MEPS 502:85-104 (2014)  -  DOI: https://doi.org/10.3354/meps10693

ABSTRACT: Global warming is now unequivocal, and studies suggest it has started to influence natural systems, including the oceans. Here, we quantify plankton changes in the North Sea for the period 1958 to 2007 using an approach we call Multi-Scale Multivariate Split Moving Window (MMS-SMW) analysis that we apply to 5 groups: (1) diatoms, (2) dinoflagellates, (3) copepods, (4) other holozooplankton and (5) meroplankton. Three temporally persistent shifts were identified in the 1960s, the 1980s and during the period 1996 to 2003. The present study therefore reveals for the first time an abrupt ecosystem shift between 1996 and 2003 in the North Sea, which had the same magnitude in terms of species response as the well-documented shift detected in the 1980s. All ecosystem shifts coincided with a significant change in hydro-climatic conditions and had consequences for the structure and the functioning of the ecosystems. We showed that the 3 shifts only impacted 40% of the plankton species or taxa considered in the analysis and that the timing of the shift varied according to the planktonic group and even among species within a group.

KEY WORDS: Abrupt ecosystem shift · Plankton · Climate · Multiscale Split Moving Window Boundary analysis