A holistic view of marine regime shifts

Abstract

Understanding marine regime shifts is important not only for ecology but also for developing marine management that assures the provision of ecosystem services to humanity. While regime shift theory is well developed, there is still no common understanding on drivers, mechanisms and characteristic of abrupt changes in real marine ecosystems. Based on contributions to the present theme issue, we highlight some general issues that need to be overcome for developing a more comprehensive understanding of marine ecosystem regime shifts. We find a great divide between benthic reef and pelagic ocean systems in how regime shift theory is linked to observed abrupt changes. Furthermore, we suggest that the long-lasting discussion on the prevalence of top-down trophic or bottom-up physical drivers in inducing regime shifts may be overcome by taking into consideration the synergistic interactions of multiple stressors, and the special characteristics of different ecosystem types. We present a framework for the holistic investigation of marine regime shifts that considers multiple exogenous drivers that interact with endogenous mechanisms to cause abrupt, catastrophic change. This framework takes into account the time-delayed synergies of these stressors, which erode the resilience of the ecosystem and eventually enable the crossing of ecological thresholds. Finally, considering that increased pressures in the marine environment are predicted by the current climate change assessments, in order to avoid major losses of ecosystem services, we suggest that marine management approaches should incorporate knowledge on environmental thresholds and develop tools that consider regime shift dynamics and characteristics. This grand challenge can only be achieved through a holistic view of marine ecosystem dynamics as evidenced by this theme issue.

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).…”

Addressing surprise and uncertain futures in marine science, marine governance, and society

“…The ecosystem science challenge More and more marine ecosystems provide examples of sudden and dramatic changes or regime shifts (Andersen et al 2008, de Young et al 2008, Conversi et al 2015. Often, regime shifts can be traced back to the interaction of environmental drivers with ecological processes , Thrush et al 2014.…”

Misapplied survey data and model uncertainty result in incorrect conclusions about the role of predation on alewife population dynamics in Lake Huron: a comment on

“…Isolating and quantifying the effects of a single factor remains challenging both because we lack critical data and multiple variables have likely interacted and contributed to alewife dynamics. Moreover, determining the relative importance of top-down or bottom-up effects is fraught with difficulty (Allen 2015), and a more holistic approach has been advocated for investigating the role of exogenous drivers and internal mechanisms in explaining ecosystem change (Conversi et al 2014). He et al (2015) argue that "predation played an important role in the alewife collapse during 2003 in the main basin of Lake Huron and remained important in suppressing their abundance in subsequent years", but their misapplication of the trawl survey data makes this an unsubstantiated conclusion.…”