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Synchronous Regime Shifts Across European Seas

Final Report Summary - SYNRESH (Synchronous Regime Shifts Across European Seas)

Regime shifts are sudden, substantial, and temporally persistent changes in the state of ecosystems [1]. They involve large-scale reorganizations in the structure and function of the biological components in ecosystems [2-4]. In the oceanic realm, regime shifts have been reported in most basins where long time series of data are available, both in the northern [5-15] and the southern hemispheres [16, 17]. They have also been reported in limnological, estuarine, and terrestrial ecology. These phenomena do not just interest scientists, but managers as well, since such shifts can have extensive impacts on local economies.

Recent research has found that many marine regime shifts occurred quasi-simultaneously, raising the question about global-scale environmental forcing. In particular, all European seas seem to have undergone regime shifts in the late 1980s [10], and fishery population synchronies have been observed between ocean basins [18].

The project SYNRESH has a dual, scientific and policy focus aiming to: (i) address via a comparative, inter-basin approach the question of large-scale synchrony in regime shift timing and its drivers and (ii) link science to marine policy and translate research into policy suggestions.

Data from eleven marine pelagic ecosystems in the northern hemisphere were collected for inter-basin comparisons: the North Sea, the Baltic Sea, the northern Adriatic Sea (eastern Mediterranean Sea), the Ligurian Sea (western Mediterranean Sea), the northern and southern ECOMON areas from Gulf of Maine to Mid-Atlantic (western Atlantic); the California Current (eastern Pacific), the eastern and western Pacific Rim, and the Oyashio Current and transition Zone (western Pacific). These data sets represent the longest time series of pelagic data in the northern hemisphere, ranging from 1960s to 2000s. This study was the first time the datasets were analysed jointly.

The same statistical methodology, described in [19], was applied for the first time to all 11 marine systems, aiming to answer the questions whether regime shifts occurred in all systems, whether they were co-occurring, and the possible mechanisms behind these phenomena. The results of these analyses have provided a varied picture: there is evidence for quasi-synchronicity of regime shifts, both within and between ocean basins, however, the precise year of the shifts varies somewhat from one basin to another, and these shifts lie embedded within considerable regional variability at both year-to-year and lower-frequency time scales. Of particular relevance is the late 1980s period, when regime shifts are identified in the majority of the basins around the world (7 out of 11).

Further analyses where developed in order to identify possible synchronizing mechanisms. The main biological signals (BioPCs) were extracted by Principal Component Analysis (PCA) on the first 3 PCs of all systems combined and were analysed in relation to changes in several northern hemisphere climatic signals, e.g. the Northern Hemisphere Temperature, the Arctic Oscillation, the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation, and northern hemispheric temperatures, winds and sea level pressures. The results of these analyses suggest that the main factor synchronizing the regime shifts on large scales is the northern hemisphere temperature, however, changes in atmospheric pressure patterns over the Arctic also seem to act as an important driver for the biological systems and might also influence temperature changes. Further investigation is required to distinguish their relative roles.

These results have also highlighted the need for better understanding the synergistic relations between drivers. To address this point, an experimental methodology based on the Genetic Programming (GP) technique was tested using the North Sea [20] as a case study. A comprehensive collection of 87, bottom-up and top-down potential drivers was used in this GP experiment to approximate the abundance of Calanus finmarchicus. The resulting new model [20] identified three potential drivers of C. finmarchicus at the North Sea scale: predators (herring abundance and biomass), temperature (SST), and circulation (N. Atlantic flow in the North Sea). This suggests that C. finmarchicus is controlled by multiple drivers, top-down (predators) and bottom-up drivers, including processes the affect the species niche (temperature) and the species transport into the North Sea.

IMPLICATIONS OF THE RESULTS
These results indicate the possibility of quasi synchronicity in the pelagic response to large scale drivers (temperature, pressure patterns). “Quasi” means that the year of the shift is not exact, but somewhat varies from basin to basin, and that not all basins may be part of it, although the majority are. The implications of the quasi-synchronicity in the reorganizations of pelagic ecosystems can be influential. First, it indicates the possibility of biological teleconnections between unconnected basins; in other words, pelagic populations may respond within a short period to some supra-basin signal. Second, these results indicate the importance of large-scale drivers (e.g. climate pressure variations, climate warming) in driving pelagic community variability. In fact, local drivers (fishing, eutrophication, pollution) obviously cannot explain basin-scale teleconnections. However, data on local drivers were not available for most basins in this study so they can still have an important role, for example, for setting the preconditions for a system shift. Third, teleconnections in the biological realm across marine basins are not yet considered a possibility in main stream science and therefore are not incorporated in biological or physical models; however, this possibility should now be taken into consideration.

This work also stresses the importance of analysing at the same time multiple types of drivers in order to provide results that are not biased by the variables selected. Most of the research normally uses a few of the proposed drivers.

The analyses in this work highlight the importance of forwarding the field of the prediction of regime shifts, which is still in an infancy stage. As a policy preliminary response to the topic of abrupt state changes, we suggest to develop indicators of basin resilience (i.e. its capacity to return to its normal state after a perturbation) and of early warnings for regime shifts. This work also shows the necessity of distinguishing local from large-scale drivers and pressures, as they will need different types of marine ecosystem protection strategies and policy responses.

Finally, a major, unplanned for, success of SYNRESH has been the approval of a thematic issue on “Marine regime shifts around the globe: theory, drivers, and impacts” to be published (2014) on the journal Philosophical Transactions B (http://rstb.royalsocietypublishing.org).

Additional successes include 2 special session/workshop in two international conferences:
RESILIENCE 2014 - Montpellier, France, May 4-8, 2014, Session: Marine regime shifts around the globe: theory, drivers, and impacts. Session chairs: Albert Norström, Magnus Nyström, Alessandra CONVERSI, and
IMBER Open Science Conference 2014. Bergen, Norway 23-27 June 2014, http://www.imber.info/index.php/Meetings/IMBER-OSC-2014/Sessions-Workshops/ Marine-regime-shifts-around-the-globe-thesocietal-challenges (Workshop "Marine regime shifts around the globe: the societal challenges". Conveners: Alessandra CONVERSI, Christian Möllmann, Martin Edwards, Carl Folke, and Sebastian Villasante).

TARGET GROUPS: It is expected that the results of the project SYNRESH will be of interest for oceanographers, modellers, marine planners, and marine managers.

CONTACT: Dr. Alessandra Conversi, Marie Curie Fellow in the project SYNRESH.
Currently Senior Researcher at the National Research Council of Italy (CNR) – ISMAR,
a.conversi@ismar.cnr.it.

CITED REFERENCES
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19. Beaugrand G., Conversi A., Chiba S., Edwards M., Fonda-Umani S., Greene C.H. Mantua N.J. Otto S.A. Reid P.C. Stachura M., et al. Submitted Synchronous marine pelagic regime shifts in the Northern Hemisphere. Philosphical Transactions of the Royal Society B
20. Papworth D., Marini S., Conversi A. in prep. Declining Calanus: What is driving Calanus finmarchicus abundance in the central North Sea? A new model based on Genetic Programming. To be submitted to Global Change Biology.
21. Rees S., Fletcher S., Glegg G., Marshall C., Rodwell L., Jefferson R., Campbell M., Langmead O., Ashley M., Bloomfield H., et al. 2013 Priority questions to shape the marine and coastal policy research agenda in the United Kingdom. Marine Policy 38, 531-537.
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