Climate and Local Hydrography Underlie Recent Regime Shifts in Plankton Communities off Galicia (NW Spain)

Antonio Bode,Marta M. Varela,Manuel Ruíz-Villarreal,Luz María García García,Mar Nieto-Cid,Maria Ángeles Louro,Marta Álvarez

doi:10.3390/oceans1040014

Antonio Bode, Marta M. Varela + Show 5 more

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https://doi.org/10.3390/oceans1040014

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Abstract

A 29-year-long time series (1990–2018) of phyto- and zooplankton abundance and composition is analyzed to uncover regime shifts related to climate and local oceanography variability. At least two major shifts were identified: one between 1997 and 1998, affecting zooplankton group abundance, phytoplankton species assemblages and climatic series, and a second one between 2001 and 2002, affecting microzooplankton group abundance, mesozooplankton species assemblages and local hydrographic series. Upwelling variability was relatively less important than other climatic or local oceanographic variables for the definition of the regimes. Climate-related regimes were influenced by the dominance of cold and dry (1990–1997) vs. warm and wet (1998–2018) periods, and characterized by shifts from low to high life trait diversity in phytoplankton assemblages, and from low to high meroplankton dominance for mesozooplankton. Regimes related to local oceanography were defined by the shift from relatively low (1990–2001) to high (2002–2018) concentrations of nutrients provided by remineralization (or continental inputs) and biological production, and shifts from a low to high abundance of microzooplankton, and from a low to high trait diversity of mesozooplankton species assemblages. These results align with similar shifts described around the same time for most regions of the NE Atlantic. This study points out the different effects of large-scale vs. local environmental variations in shaping plankton assemblages at multiannual time scales.

Highlights

Ecosystem regime shifts, or “sudden, dramatic, long-lasting changes in ecosystem structure and function” [1], represent changes in state that may be irreversible
This study reports, for the first time, multiple regime shifts in plankton assemblages off NW Iberia for the last 29 years
The fact that some of the shifts were mainly related to climate, while others were concurrent with changes in local oceanographic variables, may be due to time lags in the response of the ocean, and to the particular conditions of the studied sites

Summary

Introduction

“sudden, dramatic, long-lasting changes in ecosystem structure and function” [1], represent changes in state that may be irreversible. Earlier theories implied that the ecosystem alternated between two stable states depending on the intensity of the attractor variables and feedback mechanisms, while recent studies reveal rather more complex stepwise changes [2]. Most of the existing studies point to climatic oscillations as major drivers of these shifts [3,4,5]. Recognizing shifts is important when interpreting past changes and predicting future states (e.g., those related to climate change), as they provide the basis for management and the development of conservation policies [8,9]. Recent evidence points to a quasi-synchronicity in Oceans 2020, 1, 181–197; doi:10.3390/oceans1040014 www.mdpi.com/journal/oceans

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