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Ecological resilience is the capability of an ecosystem to maintain the same structure and function and avoid crossing catastrophic tipping points (i.e. undergoing irreversible regime shifts). While fundamental for management, concrete ways to estimate and interpret resilience in real ecosystems are still lacking. Here, we develop an empirical approach to estimate resilience based on the stochastic cusp model derived from catastrophe theory. The cusp model models tipping points derived from a cusp bifurcation. We extend cusp in order to identify the presence of stable and unstable states in complex natural systems. Our Cusp Resilience Assessment (CUSPRA) has three characteristics: (i) it provides estimates on how likely a system is to cross a tipping point (in the form of a cusp bifurcation) characterized by hysteresis, (ii) it assesses resilience in relation to multiple external drivers and (iii) it produces straightforward results for ecosystem-based management. We validate our approach using simulated data and demonstrate its application using empirical time series of an Atlantic cod population and marine ecosystems in the North Sea and the Mediterranean Sea. We show that Cusp Resilience Assessment is a powerful method to empirically estimate resilience in support of a sustainable management of our constantly adapting ecosystems under global climate change. [ABSTRACT FROM AUTHOR]

Background: Anthropogenic pressures on marine ecosystems have increased over the last 75 years and are expected to intensify in the future with potentially dramatic cascading consequences for human societies. It is therefore crucial to rebuild marine life-support systems and aim for future healthy ecosystems. Nowadays, there is a reasonable understanding of the impacts of human pressure on marine ecosystems; but no studies have drawn an integrative retrospective analysis of the marine research on the topic. A systematic consolidation of the literature is therefore needed to clearly describe the scientific knowledge clusters and gaps as well as to promote a new era of integrative marine science and management. We focus on the five direct anthropogenic drivers of biodiversity loss defined by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES): (1) climate change; (2) direct exploitation; (3) pollution; (4) biological invasions; and (5) sea-use change. Our systematic map's regional focus lies on the North Sea, which is among the most impacted marine ecosystems around the globe. The goal of the present study is to produce the first comprehensive overview of how marine research on anthropogenic drivers in the North Sea has grown and changed over the past 75 years. Ultimately, this systematic map will highlight the most urgent challenges facing the North Sea research domain. Methods: The search will be restricted to peer-reviewed articles, reviews, meta-analyses, book chapters, book reviews, proceeding papers and grey literature using the most relevant search engines for literature published between 1945 and 2020. All authors will participate in the adjustment of the search in order to consider all relevant studies analyzing the effect of the direct anthropogenic drivers on the North Sea marine ecosystem. The references will be screened for relevance according to a predefined set of eligibility/ineligibility criteria by a pool of six trained reviewers. At stage one, each abstract and title will be independently screened by two reviewers. At stage two, potentially relevant references will be screened in full text by two independent reviewers. Subsequently, we will extract a suite of descriptive meta-data and basic information of the relevant references using the SysRev platform. The systematic map database composed will provide the foundation for an interactive geographical evidence map. Moreover, we will summarize our findings with cross-validation plots, heat maps, descriptive statistics, and a publicly available narrative synthesis. The aim of our visualization tools is to ensure that our findings are easily understandable by a broad audience. [ABSTRACT FROM AUTHOR]

Collapses and regime changes are pervasive in complex systems (such as marine ecosystems) governed by multiple stressors. The demise of Atlantic cod (Gadus morhua) stocks constitutes a text book example of the consequences of overexploiting marine living resources, yet the drivers of these nearly synchronous collapses are still debated. Moreover, it is still unclear why rebuilding of collapsed fish stocks such as cod is often slow or absent. Here, we apply the stochastic cusp model, based on catastrophe theory, and show that collapse and recovery of cod stocks are potentially driven by the specific interaction between exploitation pressure and environmental drivers. Our statistical modelling study demonstrates that for most of the cod stocks, ocean warming could induce a nonlinear discontinuous relationship between fishing pressure and stock size, which would explain hysteresis in their response to reduced exploitation pressure. Our study suggests further that a continuing increase in ocean temperatures will probably limit productivity and hence future fishing opportunities for most cod stocks of the Atlantic Ocean. Moreover, our study contributes to the ongoing discussion on the importance of climate and fishing effects on commercially exploited fish stocks, highlighting the importance of considering discontinuous dynamics in holistic ecosystem-based management approaches, particularly under climate change. [ABSTRACT FROM AUTHOR]

Understanding spatio-temporal dynamics of biotic communities containing large numbers of species is crucial to guide ecosystem management and conservation efforts. However, traditional approaches usually focus on studying community dynamics either in space or in time, often failing to fully account for interlinked spatio-temporal changes. In this study, we demonstrate and promote the use of tensor decomposition for disentangling spatio-temporal community dynamics in long-term monitoring data. Tensor decomposition builds on traditional multivariate statistics (e.g. Principal Component Analysis) but extends it to multiple dimensions. This extension allows for the synchronized study of multiple ecological variables measured repeatedly in time and space. We applied this comprehensive approach to explore the spatio-temporal dynamics of 65 demersal fish species in the North Sea, a marine ecosystem strongly altered by human activities and climate change. Our case study demonstrates how tensor decomposition can successfully (i) characterize the main spatio-temporal patterns and trends in species abundances, (ii) identify sub-communities of species that share similar spatial distribution and temporal dynamics, and (iii) reveal external drivers of change. Our results revealed a strong spatial structure in fish assemblages persistent over time and linked to differences in depth, primary production and seasonality. Furthermore, we simultaneously characterized important temporal distribution changes related to the low frequency temperature variability inherent in the Atlantic Multidecadal Oscillation. Finally, we identified six major sub-communities composed of species sharing similar spatial distribution patterns and temporal dynamics. Our case study demonstrates the application and benefits of using tensor decomposition for studying complex community data sets usually derived from large-scale monitoring programs. [ABSTRACT FROM AUTHOR]

How have North Sea skate and shark assemblages changed since the early 20th century when bottom trawling became widespread, whilst their environment became increasingly impacted by fishing, climate change, habitat degradation and other anthropogenic pressures? This article examines long-term changes in the distribution and occurrence of the elasmobranch assemblage of the southern North Sea, based on extensive historical time series (1902-2013) of fishery-independent survey data. In general, larger species (thornback ray, tope, spurdog) exhibited long-term declines, and the largest (common skate complex) became locally extirpated (as did angelshark). Smaller species increased (spotted and starry ray, lesser-spotted dogfish) as did smooth-hound, likely benefiting from greater resilience to fishing and/or climate change. This indicates a fundamental shift from historical dominance of larger, commercially valuable species to current prevalence of smaller, more productive species often of low commercial value. In recent years, however, some trends have reversed, with the (cold-water associated) starry ray now declining and thornback ray increasing. This shift may be attributed to (i) fishing, including mechanised beam trawling introduced in the 1960s-1970s, and historical target fisheries for elasmobranchs; (ii) climate change, currently favouring warm-water above cold-water species; and (iii) habitat loss, including potential degradation of coastal and outer estuarine nursery habitats. The same anthropogenic pressures, here documented to have impacted North Sea elasmobranchs over the past century, are likewise impacting shelf seas worldwide and may increase in the future; therefore, parallel changes in elasmo-branch communities in other regions are to be expected. [ABSTRACT FROM AUTHOR]