Synchronous marine pelagic regime shifts in the Northern Hemisphere

Abstract

Regime shifts are characterized by sudden, substantial and temporally persistent changes in the state of an ecosystem. They involve major biological modifications and often have important implications for exploited living resources. In this study, we examine whether regime shifts observed in 11 marine systems from two oceans and three regional seas in the Northern Hemisphere (NH) are synchronous, applying the same methodology to all. We primarily infer marine pelagic regime shifts from abrupt shifts in zooplankton assemblages, with the exception of the East Pacific where ecosystem changes are inferred from fish. Our analyses provide evidence for quasi-synchronicity of marine pelagic regime shifts both within and between ocean basins, although these shifts lie embedded within considerable regional variability at both year-to-year and lower-frequency time scales. In particular, a regime shift was detected in the late 1980s in many studied marine regions, although the exact year of the observed shift varied somewhat from one basin to another. Another regime shift was also identified in the mid- to late 1970s but concerned less marine regions. We subsequently analyse the main biological signals in relation to changes in NH temperature and pressure anomalies. The results suggest that the main factor synchronizing regime shifts on large scales is NH temperature; however, changes in atmospheric circulation also appear important. We propose that this quasi-synchronous shift could represent the variably lagged biological response in each ecosystem to a large-scale, NH change of the climatic system, involving both an increase in NH temperature and a strongly positive phase of the Arctic Oscillation. Further investigation is needed to determine the relative roles of changes in temperature and atmospheric pressure patterns and their resultant teleconnections in synchronizing regime shifts at large scales.

Large scale, synchronous variability of marine fish populations driven by commercial exploitation

“…These scales are comparable to those of climate forcing in the NWA and NEA (22)(23)(24)(29)(30)(31). Thus, these analyses reveal that, contrary to the prevailing assumption (2,16,17), the scales of fishing mortality are equivalent to those of atmosphere-ocean forcing, and could account for a significant portion of the large-scale synchrony that prevails in these cod stocks.…”

“…In a recent comprehensive literature review (12) it was concluded that "it is well understood by marine scientists that climate variability is a strong driver of changes in fish populations and in fisheries." Although we do not dispute the potential importance of climate, the possibility that commercial exploitation could contribute significantly to these variations (13)(14)(15) has been largely dismissed, the assumption being that fishing mortality could not vary coherently at these scales (2,16,17). Other researchers have argued that estimates of exploitation rates often do not exist or are difficult to obtain, thereby limiting the incorporation of such effects into climate-related analyses of fish population dynamics (18).…”

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

“…In the North Sea [38] and Barents Sea [39], spatial downscaling of population models relating environmental and predation dynamics on key species have illustrated that relationships such as the apparent increased role of predation at lower water temperatures, first reported in among-system comparisons [40], are mirrored at smaller spatial scale orders of magnitude (figures 2 and 3). Therefore, in addition to examinations of commonalities in the timing of regime shifts [17,30], testing for important spatial variation within systems should be undertaken by downscaling potential relationships identified at larger spatial scales, as outlined using the Eastern Scotian Shelf as a future case study (figure 4). Future analyses will benefit from the application of such approaches to complement other strong tests of potential mechanisms [32,43,57] and assess their generality both among and within marine ecosystems, with the goal of anticipating future regime shifts and the factors that accentuate or thwart them.…”

“…R. Soc. B 370: 20130271 [11,[26][27][28][29] and continue to provide insight into the timing [17,30] and responses of large marine ecosystems and of marine fisheries to changing ocean conditions and exploitation that together are known to contribute to regime shifts [17,30,31]. This enhanced activity is partly due to the increasing availability of timeseries data for ocean climate and of survey-derived geospatial information for multiple trophic levels, and an expanding array of analytical frameworks and detection methods [2,3,7,32] that have allowed researchers to determine whether and where regime shifts have occurred.…”

Globalization, marine regime shifts and the Soviet Union

“…However, we propose that the fisheries-related dynamics of global key actors like the Soviet Union can serve an interesting complement to analyses of global and regional synchrony of regime shifts (cf. [35]). …”