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Ecological communities can be stable over multiple generations, or rapidly shift into structurally and functionally different configurations. In kelp forest ecosystems, overgrazing by sea urchins can abruptly shift forests into alternative states that are void of macroalgae and primarily dominated by actively grazing sea urchins. Beginning in 2014, a sea urchin outbreak along the central coast of California resulted in a patchy mosaic of remnant forests interspersed with sea urchin barrens. In this study, we used a 14-year subtidal monitoring dataset of invertebrates, algae, and fishes to explore changes in community structure associated with the loss of forests. We found that the spatial mosaic of barrens and forests resulted in a region-wide shift in community structure. However, the magnitude of kelp forest loss and taxonomic-level consequences were spatially heterogeneous. Taxonomic diversity declined across the region, but there were no declines in richness for any group, suggesting compositional redistribution. Baseline ecological and environmental conditions, and sea urchin behaviour, explained the persistence of forests through multiple stressors. These results indicate that spatial heterogeneity in preexisting ecological and environmental conditions can explain patterns of community change.

This study aimed at testing the hypothesis that free-floating plants may facilitate the growth of submerged plants under hypertrophic conditions and intermediate plant density. The effects of Lemna presence on the growth of two submerged plants (Elodea nuttallii and Ceratophyllum demersum) over a nitrogen gradient were experimentally investigated. This was complemented with analysing the presence of C. demersum and E. nuttallii in Hungary and in Germany in relation to the density of free-floating plants. Results showed a negative exponential pattern between underwater light intensity and Lemna cover. Ceratophyllum and Elodea relative growth rate decreased with increasing nitrogen concentrations and additional low Lemna density stimulated Ceratophyllum and suppressed Elodea. Elodea decreased linearly with Lemna density while Ceratophyllum showed a unimodal response. Total algal biomass (epiphytic and planktonic) was higher in Ceratophyllum than in Elodea treatments and decreased rapidly with increasing Lemna density. The field studies showed a positive relationship between Ceratophyllum and a negative one between Elodea and free-floating plant cover. This study clearly showed that free-floating plants can have either facilitating or inhibiting impact on the growth of submerged plants depending on cover density and macrophyte species. The facilitating effect on Ceratophyllum is most likely due to suppressing epiphytic algal growth.

The global movement for ecosystem restoration has gained momentum in response to the Bonn Challenge (2010) and the UN Decade on Ecosystem Restoration (UNDER, 2021–2030). While several science-based guidelines exist to aid in achieving successful restoration outcomes, significant variation remains in the outcomes of restoration projects. Some of this disparity can be attributed to unexpected responses of ecosystem components to planned interventions. Given the complex nature of ecosystems, we propose that concepts from Complex Systems Science (CSS) that are linked to non-linearity, such as regime shifts, ecological resilience and ecological feedbacks, should be employed to help explain this variation in restoration outcomes from an ecological perspective. Our framework, Explore Before You Restore, illustrates how these concepts impact restoration outcomes by influencing degradation and recovery trajectories. Additionally, we propose incorporating CSS concepts into the typical restoration project cycle through a CSS assessment phase and suggest that the need for such assessment is explicitly included in the guidelines to improve restoration outcomes. To facilitate this inclusion and make it workable by practitioners, we describe indicators and methods available for restoration teams to answer key questions that should make up such CSS assessment. In doing so, we identify key outstanding science and policy tasks that are needed to further operationalize CSS assessment in restoration. Synthesis and applications. By illustrating how key Complex Systems Science (CSS) concepts linked to non-linear threshold behaviour can impact restoration outcomes through influencing recovery trajectories, our framework Explore Before You Restore demonstrates the need to incorporate Complex Systems thinking in ecosystem restoration. We argue that inclusion of CSS assessment into restoration project cycles, and more broadly, into international restoration guidelines, may significantly impr

Aim The so-called regime shifts in North Sea plankton communities provide an important historical case study to understand marine regime shifts. Previous studies characterized regime shifts using a variety of community metrics (e.g., indicator species abundances, taxonomic composition and chlorophyll biomass) but left the functional traits of plankton unassessed. Here, we explicitly re-assess the historically recognized North Sea regime shifts through the lens of plankton functional traits to gain a better understanding of these events. Location The North Sea (NW European shelf). Time period 1958–2018, focusing on the 1980s and 1996–2003 regime shifts. Major taxa studied Marine phyto- and zooplankton. Methods We compute trait spaces for both phyto- and zooplankton of the North Sea using traits from the literature and a Gower's distance-based method. Using abundance data from the Continuous Plankton Recorder Survey, we then compute monthly time series of the centroids of the communities, an indicator of functional composition. We then use principal component analysis on the centroids to assess the main temporal changes in plankton functional composition associated with the 1980s and 1996–2003 regime shifts. Results Little change in plankton functional composition was associated with the 1980s regime shift. In contrast, the functional composition of plankton communities changed markedly after the 1996–2003 regime shift, with an increase in the summer relative abundance of non-motile autotrophs (i.e., diatoms) and the spring relative abundance of meroplankton. Main conclusions The North Sea regime shifts were not associated systematically with changes in functional composition, calling into question the definition of regime shifts and illustrating the importance of taking different metrics into account to interpret ecological events accurately. Taking into account functional composition, we interpret the 1980s so-called regime shift as a latitudinal shift in communitie

Aim The so-called regime shifts in North Sea plankton communities provide an important historical case study to understand marine regime shifts. Previous studies characterized regime shifts using a variety of community metrics (e.g., indicator species abundances, taxonomic composition and chlorophyll biomass) but left the functional traits of plankton unassessed. Here, we explicitly re-assess the historically recognized North Sea regime shifts through the lens of plankton functional traits to gain a better understanding of these events. Location The North Sea (NW European shelf). Time period 1958–2018, focusing on the 1980s and 1996–2003 regime shifts. Major taxa studied Marine phyto- and zooplankton. Methods We compute trait spaces for both phyto- and zooplankton of the North Sea using traits from the literature and a Gower's distance-based method. Using abundance data from the Continuous Plankton Recorder Survey, we then compute monthly time series of the centroids of the communities, an indicator of functional composition. We then use principal component analysis on the centroids to assess the main temporal changes in plankton functional composition associated with the 1980s and 1996–2003 regime shifts. Results Little change in plankton functional composition was associated with the 1980s regime shift. In contrast, the functional composition of plankton communities changed markedly after the 1996–2003 regime shift, with an increase in the summer relative abundance of non-motile autotrophs (i.e., diatoms) and the spring relative abundance of meroplankton. Main conclusions The North Sea regime shifts were not associated systematically with changes in functional composition, calling into question the definition of regime shifts and illustrating the importance of taking different metrics into account to interpret ecological events accurately. Taking into account functional composition, we interpret the 1980s so-called regime shift as a latitudinal shift in communitie

The spatial structuring of seabird populations makes individual colonies very dependent on regional factors. That is especially the case in small edge populations located far from large colonies. We analysed retrospectively the poorly known collapse, some 50 years ago (around 1962-1973), of a relatively small population of breeding common guil-lemots (Uria aalge) located at their southernmost limit of distribution in Europe (NW Iberia). We assumed that guillemots behaved locally as facultative specialists in small pelagic fish due to the occurrence of a strong clupeid fishery, and we studied the association between the guillemot collapse and annual regional landings of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), used as a proxy of total stock size. The overall relationship between ln-transformed guillemot counts (May-June) and ln-transformed sardine landings (May-October) was stronger than the fit on untrans-formed variables (r2=0.52 vs. 0.27), indicating an exponential relationship between the non-transformed variables. This relationship was somewhat stronger and linear after the collapse, when only a few tens of guillemots remaining (r2=0.60). A strong regime shift in sardine landings was detected in 1968 and also in anchovy landings in 1969. The overall relationship between guillemot numbers and anchovy landings was linear and strong (r2=0.72) but completely dependent on the large 1960s estimate of guillemots. However, no relationship was found between guillemot numbers and anchovy landings (April-June) after the guillemot collapse. The most likely period for the guillemot collapse was therefore 1968-1970, as seabird colonies are known to collapse immediately after their staple prey crashes. Local guillemot colonies were not sub-sequently rescued by immigration and have remained empty or almost empty until present, showing the high sensitivity of edge populations to environmental variability at the regional scale.

Shallow lakes are known for sudden shifts between a desired clear and an undesired turbid state despite only incremental changes in the underlying drivers. Such sudden shifts are a major challenge for lake managers who can be confronted with abrupt losses of desired ecosystem services without easily observable warning signals. Predictive tools for the loss of ecosystem resilience are vital to respond with timely mitigation measures and avert a shift to the undesired state. Early-warning indicators (EWIs) have faithfully preceded critical transitions in minimal models but have proven more elusive in real-world data, suggesting a mismatch between measurement strategy and the detectability of EWIs. Here, we capitalize on data simulated using the aquatic ecosystem model PCLake+ which represents real systems more closely than reductionistic models and which allows the generation of critical transitions in response to gradual changes in phosphorus load. We tested the effect of different sampling intervals (daily to yearly) on the detection of three often-used EWIs across a range of food web and nutrient-related variables. Moreover, we included one integrated sampling interval (yearly average of daily measurements) to represent time-integrated measurements. EWIs generally performed better at shorter intervals (daily, weekly) but integrated measurements over the year also proved suitable to detect oncoming state shifts. We propose that lake managers should aim for high-frequency measurements of variables that can be easily and cheaply measured (e.g. oxygen, Secchi) or, alternatively, focus on integrated approaches using passive samplers or sedimented material.

Fertilizers, pesticides and global warming are threatening freshwater aquatic ecosystems. Most of these are shallow ponds or slow-flowing streams or ditches dominated by submerged macrophytes, periphyton or phytoplankton. Regime shifts between the dominance of these primary producers can occur along a gradient of nutrient loading, possibly triggered by specific disturbances interfering with their competitive interactions. However, phytoplankton dominance is less desirable due to lower biodiversity and poorer ecosystem function and services. In this study, we combined a microcosm experiment with a process-based model to test three hypotheses: 1) agricultural run-off (ARO), consisting of nitrate and a mixture of organic pesticides and copper, differentially affects primary producers and enhances the risk of regime shifts, 2) warming increases the risk of an ARO-induced regime shift to phytoplankton dominance and 3) custom-tailored process-based models support mechanistic understanding of experimental results through scenario comparison. Experimentally exposing primary producers to a gradient of nitrate and pesticides at 22°C and 26°C supported the first two hypotheses. ARO had direct negative effects on macrophytes, while phytoplankton gained from warming and indirect effects of ARO like a reduction in the competitive pressure exerted by other groups. We used the process-based model to test eight different scenarios. The best qualitative fit between modeled and observed responses was reached only when taking community adaptation and organism acclimation into account. Our results highlight the importance of considering such processes when attempting to predict the effects of multiple stressors on natural ecosystems.

Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run-off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment-bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance.Using a full-factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured.We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO-related effects on macrophytes under sediment exposure.Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid cond

[Abstract] The spatial structuring of seabird populations makes individual colonies very dependent on regional factors. That is especially the case in small edge populations located far from large colonies. We analysed retrospectively the poorly known collapse, some 50 years ago (around 1962-1973), of a relatively small population of breeding common guillemots (Uria aalge) located at their southernmost limit of distribution in Europe (NW Iberia). We assumed that guillemots behaved locally as facultative specialists in small pelagic fish due to the occurrence of a strong clupeid fishery, and we studied the association between the guillemot collapse and annual regional landings of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), used as a proxy of total stock size. The overall relationship between ln-transformed guillemot counts (May-June) and ln-transformed sardine landings (May-October) was stronger than the fit on untransformed variables (r2=0.52 vs. 0.27), indicating an exponential relationship between the non-transformed variables. This relationship was somewhat stronger and linear after the collapse, when only a few tens of guillemots remaining (r2=0.60). A strong regime shift in sardine landings was detected in 1968 and also in anchovy landings in 1969. The overall relationship between guillemot numbers and anchovy landings was linear and strong (r2=0.72) but completely dependent on the large 1960s estimate of guillemots. However, no relationship was found between guillemot numbers and anchovy landings (April-June) after the guillemot collapse. The most likely period for the guillemot collapse was therefore 1968-1970, as seabird colonies are known to collapse immediately after their staple prey crashes. Local guillemot colonies were not subsequently rescued by immigration and have remained empty or almost empty until present, showing the high sensitivity of edge populations to environmental variability at the regional scale., [Resumen] Las poblaciones de aves marinas están espacialmente estructuradas y eso hace que las colonias individuales dependan mucho de factores regionales. Ese es especialmente el caso en pequeñas poblaciones ubicadas lejos de grandes colonias. Aquí analizamos retrospectivamente el colapso de una población relativamente pequeña de araos comunes (Uria aalge) reproductores, ubicada en su límite de distribución sur en Europa (NO de Iberia), sucedido hace unos 50 años (alrededor de 1962-1973). Asumimos que los araos reproductores se comportaron localmente como especialistas facultativos en el consumo de peces pelágicos pequeños debido a la existencia de una potente pesquería de clupeidos y estudiamos la asociación entre el colapso del arao y los desembarcos regionales anuales de sardina (Sardina pilchardus) y boquerón (Engraulis encrasicolus), utilizados como un proxy del tamaño total del stock. La relación general entre los conteos de araos (mayo-junio), transformados mediante el logaritmo neperiano, y los desembarcos de sardina (mayo-octubre) transformados, fue más fuerte que el ajuste de las variables no transformadas (r2=0.52 frente a 0.27), lo que indica una relación exponencial entre las variables no transformadas. Esta relación fue algo más fuerte y lineal después del colapso, cuando solo quedaron unas pocas decenas de araos (r2=0,60). Se detectó un fuerte cambio de régimen en los desembarcos de sardina en 1968 y también en los de boquerón en 1969. La relación entre el número de araos y los desembarcos de boquerón fue lineal y fuerte (r2=0.72). Sin embargo, no se encontró relación entre el número de araos y los desembarcos de boquerón (abril-junio) después del colapso del arao. La fecha más probable para el colapso del arao, por lo tanto, fue el período 1968-1970, ya que las colonias de aves marinas colapsan inmediatamente después de que sus presas principales hayan colapsado. Las colonias locales de araos no fueron rescatadas posteriormente por inmigración y han

There has so far been no shared understanding of validity in agent-based simulation. We here conceptualise validation as systematically substantiating the premises on which conclusions from simulation analysis for a particular modelling context are built. Given such a systematic perspective, validity of agent-based models cannot be ensured if validation is merely understood as an isolated step in the modelling process. Rather, valid conclusions from simulation analysis require context-adequate method choices at all steps of the simulation analysis including model construction, model and parameter inference, uncertainty analysis and simulation. We present a twelve-step protocol to highlight the (often hidden) premises for methodological choices and their link to the modelling context. It is designed to aid modelers in understanding their context and in choosing and documenting context-adequate and mutually consistent methods throughout the modelling process. Its purpose is to assist reviewers and the community as a whole in assessing and discussing context-adequacy., Multi Actor Systems, Policy Analysis

As coastal social-ecological systems (SES) are used for many different purposes and subject to different stressors, they are also among the most vulnerable and change the most rapidly. To achieve resilience, coastal areas require adaptive management based on integrated interdisciplinary approaches, requiring a deep understanding of SES dynamics, i.e. the ecological and social changes that comprise synchronicities and regime shifts. For the purpose of analyzing co-evolution and regime shifts, we propose an original and operational methodology combining (i) a chronosystemic timeline approach and (ii) time series analyses based on indicators from the “Drivers-Pressures-State-Impacts-Responses” framework (14 indicators including population growth, eutrophication status, ecosystem services, management actions and climate change indicators). The methodology was tested on a SES located on the French Mediterranean coast, the Thau lagoon, whose trajectory we studied over a 5-decade period (1970–2018). Our results show that the dynamics of co-evolution and regime shifts of the SES were driven by a succession of interactions between sanitary or ecological crises and management adaptations. During the study period, this typical Mediterranean coastal SES appears to have evolved towards the multiplication of uses, improvement of water quality and more integrative management. Our methodology also highlighted three contrasting periods characterized by stable emerging properties and identified several cause-and-effect relationships, which is rare in historical analyses of SES. These cause-and-effect relationships concern major sanitary and ecological crises that have led to a reorganization of governance mechanisms and to technical remediation actions. Our approach based on long-term trajectories will help identify the conditions required for increasing the resilience of coastal SES and the best management objectives to face new challenges related to global climate change.

CONTEXT: Regardless 30 years of similar regulations and a common internal market, the diffusion of organic farming strongly differs amongst European member states. While the share of organic farmland in 2018 in Denmark and Austria was respectively 9.8% and 24.7%, in the Netherlands it was only 2.3%. OBJECTIVE: The aim of this paper was to analyze what factors may determine the very different diffusion of organic dairy farming in the Netherlands, compared to Denmark and Austria. METHODS: We applied the Technological Innovation System (TIS) framework to the case of organic dairy farming in the Netherlands, for which a literature review and interviews with key actors within the dairy value chain were carried out. To identify potential leverage points for upscaling also interviews with key actors from Denmark and Austria were held. RESULTS AND CONCLUSIONS: Various barriers in the fulfilment of the seven TIS functions of Dutch organic dairy farming could be identified. With regard to the system function market formation a diversification in certified dairy products are signaled as important factors for upscaling. The function entrepreneurial activities will benefit from an reinforcement of governmental subsidies, since farmers who convert to organic run financial risks. Regarding the function guidance of the search, more consistent and systemic governmental support is needed, since the conversion to organic encompass a regime shift rather that supporting newcomers entering the sector. SIGNIFICANCE: By studying the blocking mechanisms that hinder diffusion of organic dairy, the paper provides several leverage points that may also be applicable to the arrested diffusion of organic farming in other countries as well as the larger sustainability transition in European agriculture.

The Saudi Arabian tourism sector is growing, and its economy has flourished over the last decades. This has resulted in numerous coastal developments close to large economic centers, while many more are proposed or planned. The coastal developments have influenced the behavior of the shoreline in the past. Here we undertake a national assessment on the state of the coast of Saudi Arabia based on recent data sets on historic and future shoreline positions. While at national scale the shoreline is found to be stable over the last three decades, the Red Sea coast shows a regional-mean retreat rate while the Gulf coast shows a regional-mean prograding behavior. Detailed analysis of the temporal evolution of shoreline position at selected locations show that human interventions may have accelerated shoreline retreat along adjacent shorelines, some of which are Marine Protected Areas. Furthermore, reef-fronted coastal sections have a mean accretive shoreline change rate, while the open coast shows a mean retreat rate. Future shoreline projections under RCP 4.5 and RCP 8.5 show that large parts of the shoreline may experience an accelerated retreat or a change in its regime from either stable or sprograding to retreating. Under the high emission RCP 8.5 scenario, the length of coastline projected to retreat more than doubles along the Red Sea coast, and approximately triples along the Gulf coast in 2100. At national scale, the Saudi Arabian coastline is projected to experience regional-mean retreats of ~30 m and of ~130 m by 2050 and 2100 under both RCPs considered in this study. These results indicate that effective adaptation strategies will be required to protect areas of ecological and economic value, and that climate resilience should be a key consideration in planned or proposed coastal interventions., Coastal Engineering

Fisheries management has historically focused on the population elasticity of target fish based primarily on demographic modeling, with the key assumptions of stability in environmental conditions and static trophic relationships. The predictive capacity of this fisheries framework is poor, especially in closed systems where the benthic diversity and boundary effects are important and the stock levels are low. Here, we present a probabilistic model that couples key fish populations with a complex suite of trophic, environmental, and geomorphological factors. Using 41 years of observations we model the changes in eastern Baltic cod (Gadus morhua), herring (Clupea harengus), and Baltic sprat (Sprattus sprattus balticus) for the Baltic Sea within a Bayesian network. The model predictions are spatially explicit and show the changes of the central Baltic Sea from cod- to sprat-dominated ecology over the 41 years. This also highlights how the years 2004 to 2014 deviate in terms of the typical cod–environment relationship, with environmental factors such as salinity being less influential on cod population abundance than in previous periods. The role of macrozoobenthos abundance, biotopic rugosity, and flatfish biomass showed an increased influence in predicting cod biomass in the last decade of the study. Fisheries management that is able to accommodate shifting ecological and environmental conditions relevant to biotopic information will be more effective and realistic. Non-stationary modelling for all of the homogeneous biotope regions, while acknowledging that each has a specific ecology relevant to understanding the fish population dynamics, is essential for fisheries science and sustainable management of fish stocks.

This book provides a non-technical introduction to Unified Growth Theory (UGT), that is, the study of history as a succession of economic regimes. It first focuses on the canonical example of regime shift: the transition from the regime of Malthusian stagnation to the modern regime of sustained economic growth. Then, it broadens the perspectives on historical change by examining other regime shifts involving institutional and environmental forces. This book fills a gap in the market by providing a more accessible treatment of UGT and invites readers to explore ideas of continuity and discontinuity in history.

Recent fingerprints of Alaskan Arctic climate change include new weather patterns whose impacts propagate through the Alaskan marine ecosystem. Multiple lines of observational evidence draw attention to the last five years (2017–2021) as a remarkable period of change. Bering Sea winter and spring ice coverage was remarkably low in 2018 and 2019 associated with a shifted Aleutian Low (AL) into the western Bering Sea, and ridging of the overlying polar jet stream (PJS) that supported southerly winds and reduced ice growth. The climatological Beaufort High and associated Beaufort Gyre saw multiple winter-long collapses (2017 and 2020), the only two such events of the modern reanalysis era. In contrast, from 2012 to 2016 the AL and PJS were located southeastward across the Gulf of Alaska, which supported sea ice growth. The recent collocation of the exposed ocean surface and atmospheric anomalies supports the emergence of a regional atmospheric circulation response to sea-ice loss. We propose that the regional system shift after 2017 foreshadows the beginning of a period with an increasing frequency of major sea-ice loss events and associated impacts – floods, delayed spring blooms, and marine food chain disruptions – which is sooner than projected by climate models.

Seagrass ecosystems usually respond in a nonlinear fashion to increasing pressures and environmental changes. Feedback mechanisms operating at the ecosystem level and involving multiple interactions among the seagrass meadow, its associated community and the physical environment are known to play a major role in such nonlinear responses. Phenotypic plasticity may also be important for buffering these ecological thresholds (i.e., regime shifts) as many physiological processes show nonlinear responses to gradual environmental changes, conferring the appearance of resistance before the effects at the organism and population levels are visible. However, the potential involvement of plant plasticity in driving catastrophic shifts in seagrass ecosystems has not yet been assessed. In this study, we conducted a manipulative 6-month light-gradient experiment in the field to capture nonlinearities of the physiological and population responses of the seagrass Cymodocea nodosa to gradual light reduction. The aim was to explore if and how the photo-acclimatory responses of shaded plants are translated to the population level and, hence, to the ecosystem level. Results showed that the seagrass population was rather stable under increasing shading levels through the activation of multilevel photo-acclimative responses, which are initiated with light reduction and modulated in proportion to shading intensity. The activation of photo-physiological and metabolic compensatory responses allowed shaded plants to sustain nearly constant plant productivity (metabolic carbon balance) along a range of shading levels before losing linearity and starting to decline. The species then activated plant- and meadow-scale photo-acclimative responses and drew on its energy reserves (rhizome carbohydrates) to confer additional population resilience. However, when the integration of all these buffering mechanisms failed to counterbalance the effects of extreme light limitation, the population collapse

In aquatic ecosystems, excessive nutrient loading is a global problem that can induce regime shifts from macrophyte- to phytoplankton-dominated states with severe consequences for ecosystem functions. Most agricultural landscapes are sites of nutrient and pesticide loading, which can interact with other stressors (e.g., warming) in additive, antagonistic, synergistic or reversed forms. The effects of multiple stressors on the resilience of macrophyte-dominated states and on critical thresholds for regime shifts are, however, unknown. We test the effects of individual and combined stressors of warming, nitrate, and various pesticides typically found in agricultural run-off (ARO) on the growth of macrophytes, periphyton, and phytoplankton in microcosms. We applied a one-level replicated design to test whether ARO induces a regime shift and a multifactorial dose–response design to model stressor thresholds and disentangle stressor interactions along a gradient. The individual stressors did not induce a regime shift, but the full ARO did. Nitrate and pesticides acted synergistically, inducing a shift with increasing phytoplankton biomass and decreasing macrophyte biomass. Warming amplified this effect and lowered critical thresholds for regime shifts. Shallow aquatic ecosystems in agricultural landscapes affected by global warming thus increasingly risk shifting to a turbid, phytoplankton-dominated state, and negatively impacting ecosystem service provisioning. Multiple stressor interactions must be considered when defining safe operating spaces for aquatic systems.

Recent changes in oceanic plankton are being reported at unprecedented rates. Most changes are related to environmental factors and many were identified as driven by climate, either through natural cycles or by anthropogenic effects. However, the separation of both effects is difficult because of the small size of most observational series. Moreover, some changes are related to trends and cycles while others were perceived as system shifts, often synchronized over large spatial scales. Here, studies on observational series of plankton, with the focus in the N Atlantic, are reviewed. Two main quasi-synchronic shifts in species assemblages were identified: one in late 1980’s and a most recent one in the first decade of the new millennium. While the origin and extent of most shifts vary locally, their synchronization seems to confirm the lagged response of plankton to changes in warming and in large-scale climatic factors. Changes in species abundance patterns are generally related to the strength of currents, but also to non-linear effects of warming, the latter particularly affecting species in regions near the limits of their thermal niche. Indeed, most of the changes are attributed to trade-offs between different biological strategies. Taken together, the reviewed case studies indicate a lagged biological response to variations in the local environment driven by large-scale climate forcing. The challenges for the interpretation of future changes include the consideration of local changes in a wider regional context, variations in species life-traits and possible top-down effects of plankton predators

Ocean warming affects fisheries around the globe. Commercial fish respond to it depending on their preferences for certain temperatures. The small pelagic fish community responds faithfully to environmental changes, making it a good early warning system to understand and prevent the biological communities shift. Indeed, the occurrence of regime shift of the pelagic communities caused by environmental factors has catastrophic consequences on the society, causing changes in the economic and cultural dimensions. Here, we explored the causes of the regime shift that occurred in the small pelagic community on Madeira Island. To do so, we focused on the landings of four species that ensemble the small fish pelagic community, Boops boops, Scomber colias, Sardina pilchardus, and Trachurus picturatus, over a 40-year period (1980-2019). On the environmental side, we collected information on Sea Surface Temperature Anomaly (SSTA) and North Atlantic Oscillation data (NAO), for each year of the time series. To shed light on the causes of shift landings, we performed a set of General Additive Models to fit the nonlinear trends. Our results showed that the regime shift of the small fish pelagic community occurred in 2002, with a transition period from 2000 to 2003. Where the simultaneous factors SSTA and NAO explained up to 88.2 % of the small fish pelagic community shift, both of which were significant. This trend was unyielding despite the implemented management actions to preserve these stocks. The present findings are further evidence of the major effects of ocean warming on small pelagic catch levels. An urgent need to consider ocean warming in the proper management of fish stocks is required. The economic consequences are devastating considering the importance of small pelagic by artisanal fishermen from several geographic areas

Seagrass ecosystems usually respond in a nonlinear fashion to increasing pressures and environmental changes. Feedback mechanisms operating at the ecosystem level and involving multiple interactions among the seagrass meadow, its associated community and the physical environment are known to play a major role in such nonlinear responses. Phenotypic plasticity may also be important for buffering these ecological thresholds (i.e., regime shifts) as many physiological processes show nonlinear responses to gradual environmental changes, conferring the appearance of resistance before the effects at the organism and population levels are visible. However, the potential involvement of plant plasticity in driving catastrophic shifts in seagrass ecosystems has not yet been assessed. In this study, we conducted a manipulative 6-month light-gradient experiment in the field to capture nonlinearities of the physiological and population responses of the seagrass Cymodocea nodosa to gradual light reduction. The aim was to explore if and how the photo-acclimatory responses of shaded plants are translated to the population level and, hence, to the ecosystem level. Results showed that the seagrass population was rather stable under increasing shading levels through the activation of multilevel photo-acclimative re sponses, which are initiated with light reduction and modulated in proportion to shading intensity. The acti vation of photo-physiological and metabolic compensatory responses allowed shaded plants to sustain nearly constant plant productivity (metabolic carbon balance) along a range of shading levels before losing linearity and starting to decline. The species then activated plant- and meadow-scale photo-acclimative responses and drew on its energy reserves (rhizome carbohydrates) to confer additional population resilience. However, when the integration of all these buffering mechanisms failed to counterbalance the effects of extreme light limitation, the population collap

Tipping points are an emerging concept in climate change research and communication. However, previous research has strongly focussed on tipping points in biophysical systems, which left the potential for climate change induced socio-economic tipping points (SETPs) mostly unexplored. The objective of this thesis is to identify and assesses SETPs in order to support decision making on climate policy. A SETP is defined as “a climate change induced, abrupt change of a socio-economic system, into a new, fundamentally different state”. SETPs are characterised by: (1) stable states at two sides of a threshold; (2) a non-linear change mechanism, and (3) rapid change while passing the threshold. Examples are: the collapse of winter sports tourism, farmland abandonment, and sea-level rise-induced migration. The clearest examples of SETPs are likely to be found on small scale homogeneous systems, that can exhibit a system-wide uniform response to a climate driver. When modelling SETPs, there is an extra layer of complexity compared to biophysical tipping points, because of the complex dynamic character of the socio-economic system and the fact that humans proactively and autonomously alter the system to anticipate biophysical change. This thesis presents a stepwise approach for identification and assessment of SETPs, which in seven steps guides the researcher through key study design choices. The first application is urban water security. The essence of urban water security lies in an adequate response to partly inevitable system pressures, with well-functioning infrastructure that prevents adverse impacts such as flood damage. At the same time, in cities under pressure, like Amsterdam and Rotterdam, flood pressures may always propagate along the cause-effect chain via an unexpected mechanism. For example, a flood or near-miss experience could lead to the SETP of an abrupt house price collapse. Stepwise SETP-assessment shows that house price collapses could happen under condi

The Saudi Arabian tourism sector is growing, and its economy has flourished over the last decades. This has resulted in numerous coastal developments close to large economic centers, while many more are proposed or planned. The coastal developments have influenced the behavior of the shoreline in the past. Here we undertake a national assessment on the state of the coast of Saudi Arabia based on recent data sets on historic and future shoreline positions. While at national scale the shoreline is found to be stable over the last three decades, the Red Sea coast shows a regional-mean retreat rate while the Gulf coast shows a regional-mean prograding behavior. Detailed analysis of the temporal evolution of shoreline position at selected locations show that human interventions may have accelerated shoreline retreat along adjacent shorelines, some of which are Marine Protected Areas. Furthermore, reef-fronted coastal sections have a mean accretive shoreline change rate, while the open coast shows a mean retreat rate. Future shoreline projections under RCP 4.5 and RCP 8.5 show that large parts of the shoreline may experience an accelerated retreat or a change in its regime from either stable or sprograding to retreating. Under the high emission RCP 8.5 scenario, the length of coastline projected to retreat more than doubles along the Red Sea coast, and approximately triples along the Gulf coast in 2100. At national scale, the Saudi Arabian coastline is projected to experience regional-mean retreats of ~30 m and of ~130 m by 2050 and 2100 under both RCPs considered in this study. These results indicate that effective adaptation strategies will be required to protect areas of ecological and economic value, and that climate resilience should be a key consideration in planned or proposed coastal interventions., Coastal Engineering

Fisheries management has historically focused on the population elasticity of target fish based primarily on demographic modeling, with the key assumptions of stability in environmental conditions and static trophic relationships. The predictive capacity of this fisheries framework is poor, especially in closed systems where the benthic diversity and boundary effects are important and the stock levels are low. Here, we present a probabilistic model that couples key fish populations with a complex suite of trophic, environmental, and geomorphological factors. Using 41 years of observations we model the changes in eastern Baltic cod (Gadus morhua), herring (Clupea harengus), and Baltic sprat (Sprattus sprattus balticus) for the Baltic Sea within a Bayesian network. The model predictions are spatially explicit and show the changes of the central Baltic Sea from cod-to sprat-dominated ecology over the 41 years. This also highlights how the years 2004 to 2014 deviate in terms of the typical cod–environment relationship, with environmental factors such as salinity being less influential on cod population abundance than in previous periods. The role of macrozoobenthos abundance, biotopic rugosity, and flatfish biomass showed an increased influence in predicting cod biomass in the last decade of the study. Fisheries management that is able to accommodate shifting ecological and environmental conditions relevant to biotopic information will be more effective and realistic. Non-stationary modelling for all of the homogeneous biotope regions, while acknowledging that each has a specific ecology relevant to understanding the fish population dynamics, is essential for fisheries science and sustainable management of fish stocks.

Modified fish behaviors in response to anthropogenic stressors, such as chemicals, microplastics, acoustic emissions and fisheries, are a debated driver of change in freshwater ecosystems and oceans. Our ability to judge the severity of observed behavioral responses is hampered by limited knowledge regarding how subtle behavior modifications in prey fish affect ecosystems. Here we show that anthropogenic stressors affecting fish boldness are not expected to cause population collapse, but rather elusive effects on fish length, population biomass, reproduction and ecosystem state shifts. We use a physiologically structured population model (three trophic levels), well fed with empirical data, to simulate how previously suggested alterations of fish boldness traits due to anthropogenic stressors affect ecosystem structure. Our results suggest that these stressors may cause ecosystem structure effects, such as skewed size distributions, reduced fish biomass and reduced reproduction success, by altering the foraging behavior of fish. However, the specific structure effects depend on where the boldness-shyness continuum change occurs and on the species-specific life stages. The model also highlights somewhat counterintuitive effects leading to possible extinction of predators when the foraging behavior of the prey is hampered. We conclude that anthropogenic forcing of fish behavior may be a hidden mechanism behind ecosystem structure changes in both freshwater and marine ecosystems.

Humans are rapidly transforming the structural configuration of the planet's eco systems, but these changes and their ecological consequences remain poorly quantified in underwater habitats. Here, we show that the loss of forest-forming seaweeds and the rise of ground-covering ‘turfs’ across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Globally, turf seascapes occupied a smaller architectural trait space and were structurally more similar across regions than marine forests, evidencing habitat homogenization. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat archi tecture, as well as across disparate drivers of marine forest decline. Turf seascapes contained high sediment loads, with the miniaturization of habitat across 100s of km in mid-Western Australia resulting in reefs retaining an additional ~242 million tons of sediment (four orders of magnitude more than the sediments delivered flu vially annually). Together, this work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs.

Net sediment transport is predominantly seaward in fluvial-dominated estuaries worldwide. However, a distributary branch in the Changjiang Estuary, the North Branch, undergoes net landward sediment transport, which leads to severe channel aggradation. Its controlling mechanism and the role of human activities remain insufficiently understood, although such knowledge is necessary for better management and restoration opportunities. In this study we revisit the centennial hydro-morphodynamic evolution of the North Branch based on historical maps, field data, and satellite images and provide a synthesis of the regime change from ebb to flood dominance. The North Branch was once a major river and ebb-dominant distributary channel. Within which alternative meandering channels and sand bars developed. Deposition of river-borne sediment leads to infilling of the branch, while tidal flat embankment reduces the bankfull width and modifies the channel configuration, resulting in a profound decline in the sub-tidal flow partition rate. The North Branch then becomes tide-dominant with an occurrence of tidal bores and elongated sand ridges. Once tidal dominance is established, extensive tidal flat reclamation enhances the funnel-shaped planform, amplifying the incoming tides and initiating a positive feedback process that links tidal flat loss, sediment import, and channel aggradation. Overall, the shift in branch dominance is a combined result of a natural southeastward realignment of the deltaic distributary channels and extensive reclamation. One management option to mitigate channel aggradation is to stop the aggressive reclamation and allow tidal flats to build up, which might reduce the sediment import and eventually lead to a morphodynamic equilibrium in the longer term. Understanding the impact of tidal flat reclamation is informative for the management of similar tidal systems under strong human interference., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Coastal Engineering

This is a case study examines a possible regime shift between the Kyoto Protocol and the Paris Agreement. The study is using a theory consuming approach, with process tracing as the main instrument of analyzation. Using Keohane & Victor’s theory on regime complex, the two different regimes are highlighted: Kyoto and Paris. Applying Abbot, Green and Keohane’s theory on Organizational Ecology, help with providing interesting insights as to the causes of the shift in global environmental governance. Looking at causes for shifts in the regime, the private sector plays a central role. A framework is built by lending a model from natural science on Regime Shift, by Folke et.al. Based on the model, process tracing can be used which identifies several conferences in between Kyoto and Paris. COP 20 in Lima, COP 17 in Durban, and COP 15 in Copenhagen are shortly examined, and defined using the theories states above. The study focuses on a macro perspective on the governance of the Conferences of Parties.

Many agree that estimating portfolio risks has better estimation possibilities, than estimations on returns. Therefore investors attempts to construct better, more efficient riskmanaged portfolios by diversifying portfolios through factors rather than traditional asset classes. This entails very often in estimations of correlation matrices so complex it cannot be fully analyzed. Hierarchical clustering reduces the complexity, by only focusing on the correlations that matters. Hierarchical clustering uses graph theory, linked to unsupervised machine learning techniques. Hierarchical clustering is obtained by the suggested data and is a formation of a recursive clustering. Several hierarchical clustering methods are presented and evaluated against traditional riskbased portfolios with focus on left hand tail risk. A regime shift, based on momentum is applied to minimize drawdowns. The portfolios are tested on simulated data derived from Bootstrapping simulations and on historical data in a Walk forward optimization process. The results indicate that hierarchical clustering based portfolios are truly diversified and achieve statistically better riskadjusted performances than commonly used portfolio optimization techniques., In attempts to construct better and more efficient risk managed portfolios, investors have recently changed their focus towards estimate risk instead of forecasting return. Estimating risk usually involves a correlation matrix, too complex to be fully analyzed. Hierarchical Clustering reduces the complexity and creates diversified portfolios. Big drawdowns could be reduced with a regime shift.

Identifying and characterising dynamical regime shifts, critical transitions or potential tipping points in palaeoclimate time series is relevant for improving the understanding of often highly nonlinear Earth system dynamics. Beyond linear changes in time series properties such as mean, variance, or trend, these nonlinear regime shifts can manifest as changes in signal predictability, regularity, complexity, or higher-order stochastic properties such as multi-stability. In recent years, several classes of methods have been put forward to study these critical transitions in time series data that are based on concepts from nonlinear dynamics, complex systems science, information theory, and stochastic analysis. These include approaches such as phase space-based recurrence plots and recurrence networks, visibility graphs, order pattern-based entropies, and stochastic modelling. Here, we review and compare in detail several prominent methods from these fields by applying them to the same set of marine palaeoclimate proxy records of African climate variations during the past 5 million years. Applying these methods, we observe notable nonlinear transitions in palaeoclimate dynamics in these marine proxy records and discuss them in the context of important climate events and regimes such as phases of intensified Walker circulation, marine isotope stage M2, the onset of northern hemisphere glaciation and the mid-Pleistocene transition. We find that the studied approaches complement each other by allowing us to point out distinct aspects of dynamical regime shifts in palaeoclimate time series. We also detect significant correlations of these nonlinear regime shift indicators with variations of Earth's orbit, suggesting the latter as potential triggers of nonlinear transitions in palaeoclimate. Overall, the presented study underlines the potentials of nonlinear time series analysis approaches to provide complementary information on dynamical regime shifts in palaeoclimate an

Reducing excessive external nutrient loading is in principle the first adaptive management against eutrophication, whereas little is known about the recovery time of such intervention, especially in the context of global warming. Here, we use an ensemble approach of paleolimnological records and modeling PCLake to evaluate the recovery time of Lake Taibai, China under diverse combinations of nutrient reduction and climate change scenarios. The model was calibrated for seven sensitive parameters and further validated using the total phosphorus (TP) concentrations in sediment cores reconstructed using a diatom-TP transfer function. The paleolimnological records show that species indicative of eutrophic conditions and the diatom-inferred TP (DI-TP) were low before the 1980s and slightly increased thereafter. The calibrated model not only captures the dynamics of TP concentrations but also performs well in identifying the regime shift between the 2 alternative stable states of the lake: macrophyte-dominated (clear) and algae-dominated (turbid) states. The scenarios results suggest that lake restoration (from turbid to clear state) would take 10–20 years with an annual nutrient loading (both N and P) reduction rate of 15–25% from 2019. Meanwhile, global warming would impede the effectiveness of nutrient reduction by not only increasing the restoration time but also decreasing the vegetation restoration level (as indicated by vegetation dry weight in lake water) and critical nutrient loading for re-oligotrophication. Our results imply that in the long run, nutrient loading reduction measurement for sustainable lake restoration should be adjusted following temperature changes. The present study highlights the feasibility and relevance of a novel methodology using paleolimnological records for model calibration and projections. The modeling approach presented here may provide a better understanding and critical implications of the long-term dynamics and future rest

Many agree that estimating portfolio risks has better estimation possibilities, than estimations on returns. Therefore investors attempts to construct better, more efficient riskmanaged portfolios by diversifying portfolios through factors rather than traditional asset classes. This entails very often in estimations of correlation matrices so complex it cannot be fully analyzed. Hierarchical clustering reduces the complexity, by only focusing on the correlations that matters. Hierarchical clustering uses graph theory, linked to unsupervised machine learning techniques. Hierarchical clustering is obtained by the suggested data and is a formation of a recursive clustering. Several hierarchical clustering methods are presented and evaluated against traditional riskbased portfolios with focus on left hand tail risk. A regime shift, based on momentum is applied to minimize drawdowns. The portfolios are tested on simulated data derived from Bootstrapping simulations and on historical data in a Walk forward optimization process. The results indicate that hierarchical clustering based portfolios are truly diversified and achieve statistically better riskadjusted performances than commonly used portfolio optimization techniques., In attempts to construct better and more efficient risk managed portfolios, investors have recently changed their focus towards estimate risk instead of forecasting return. Estimating risk usually involves a correlation matrix, too complex to be fully analyzed. Hierarchical Clustering reduces the complexity and creates diversified portfolios. Big drawdowns could be reduced with a regime shift.

Net sediment transport is predominantly seaward in fluvial-dominated estuaries worldwide. However, a distributary branch in the Changjiang Estuary, the North Branch, undergoes net landward sediment transport, which leads to severe channel aggradation. Its controlling mechanism and the role of human activities remain insufficiently understood, although such knowledge is necessary for better management and restoration opportunities. In this study we revisit the centennial hydro-morphodynamic evolution of the North Branch based on historical maps, field data, and satellite images and provide a synthesis of the regime change from ebb to flood dominance. The North Branch was once a major river and ebb-dominant distributary channel. Within which alternative meandering channels and sand bars developed. Deposition of river-borne sediment leads to infilling of the branch, while tidal flat embankment reduces the bankfull width and modifies the channel configuration, resulting in a profound decline in the sub-tidal flow partition rate. The North Branch then becomes tide-dominant with an occurrence of tidal bores and elongated sand ridges. Once tidal dominance is established, extensive tidal flat reclamation enhances the funnel-shaped planform, amplifying the incoming tides and initiating a positive feedback process that links tidal flat loss, sediment import, and channel aggradation. Overall, the shift in branch dominance is a combined result of a natural southeastward realignment of the deltaic distributary channels and extensive reclamation. One management option to mitigate channel aggradation is to stop the aggressive reclamation and allow tidal flats to build up, which might reduce the sediment import and eventually lead to a morphodynamic equilibrium in the longer term. Understanding the impact of tidal flat reclamation is informative for the management of similar tidal systems under strong human interference., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Coastal Engineering

This is a case study examines a possible regime shift between the Kyoto Protocol and the Paris Agreement. The study is using a theory consuming approach, with process tracing as the main instrument of analyzation. Using Keohane & Victor’s theory on regime complex, the two different regimes are highlighted: Kyoto and Paris. Applying Abbot, Green and Keohane’s theory on Organizational Ecology, help with providing interesting insights as to the causes of the shift in global environmental governance. Looking at causes for shifts in the regime, the private sector plays a central role. A framework is built by lending a model from natural science on Regime Shift, by Folke et.al. Based on the model, process tracing can be used which identifies several conferences in between Kyoto and Paris. COP 20 in Lima, COP 17 in Durban, and COP 15 in Copenhagen are shortly examined, and defined using the theories states above. The study focuses on a macro perspective on the governance of the Conferences of Parties.

Major land use changes such as deforestation and restoration influence water resources in agriculture–forest landscapes. Changes are observed in water flows, groundwater infiltration, water quality and rainfall. Interdisciplinary water–forest research has unravelled biophysical parts of the interplay that influences forest and water resources. In this Perspective paper, we propose an expanded interdisciplinary research approach to study water and policies in agriculture–forest frontiers. The approach differs in four important aspects from previous ones: (i) a conceptual ‘frontier’ understanding; an analytical focus on (ii) agriculture and (iii) policy–water linkages; (iv) empirical attention to northern and southern countries. The approach is put into practice with the “Pendulum” framework, with interventions and the agriculture–forest frontier oscillating over time between exploitation and restoration. Through the approach, a better understanding will be provided on the dynamic interplay of water and policies in oscillating agriculture–forest frontiers, with changing outcomes for people and environment.

Humans are rapidly transforming the structural configuration of the planet's eco systems, but these changes and their ecological consequences remain poorly quantified in underwater habitats. Here, we show that the loss of forest-forming seaweeds and the rise of ground-covering ‘turfs’ across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Globally, turf seascapes occupied a smaller architectural trait space and were structurally more similar across regions than marine forests, evidencing habitat homogenization. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat archi tecture, as well as across disparate drivers of marine forest decline. Turf seascapes contained high sediment loads, with the miniaturization of habitat across 100s of km in mid-Western Australia resulting in reefs retaining an additional ~242 million tons of sediment (four orders of magnitude more than the sediments delivered flu vially annually). Together, this work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs.

Modified fish behaviors in response to anthropogenic stressors, such as chemicals, microplastics, acoustic emissions and fisheries, are a debated driver of change in freshwater ecosystems and oceans. Our ability to judge the severity of observed behavioral responses is hampered by limited knowledge regarding how subtle behavior modifications in prey fish affect ecosystems. Here we show that anthropogenic stressors affecting fish boldness, are not expected to cause population collapse, but rather elusive effects on fish length, population biomass, reproduction and ecosystem state shifts. We use a physiologically structured population model (three trophic levels), well fed with empirical data, to simulate how previously suggested alterations of fish boldness traits due to anthropogenic stressors affect ecosystem structure. Our results suggest that these stressors may cause ecosystem structure effects, such as skewed size distributions, reduced fish biomass and reduced reproduction success, by altering the foraging behavior of fish. However, the specific structure effects depend on where the boldness‐shyness continuum change occurs and on the species‐specific life‐stages. The model also highlights somewhat counterintuitive effects leading to possible extinction of predators when the foraging behavior of the prey is hampered. We conclude that anthropogenic forcing of fish behavior may be a hidden mechanism behind ecosystem structure changes in both freshwater and marine ecosystems.

A recent warning to humanity signed by >15 000 scientists identified global environmental threats that require urgent policy response from world leaders (Ripple et al 2017). Here, we document challenges and propose solutions related to ongoing shifts in natural disturbance regimes, which are both a cause and a consequence of major environmental perils. We propose the development of new disturbance management plans based on novel policies for land management, biodiversity conservation, and ecosystem restoration, which accommodate forecasted disturbance regime shifts and expected ecosystem responses.

This study explored the shift in land use from livestock farming to game farming in the Eastern Cape, South Africa, from a social-ecological regime shift perspective. A regime shift can be defined as a large, persistent change in the structure and function of the intertwined social and ecological components of a landscape. This research focused on the Amakhala game reserve as a case study to understand how the shift affected the provision of ecosystem services and human wellbeing. We used remote sensing techniques to quantify changes in vegetation and found evidence of vegetation recovery following the shift. We then conducted interviews with both landowners and farmworkers and used participatory mapping to understand their perceptions of the main drivers and social-ecological impacts of the shift in land use. Social narratives revealed stark differences in different stakeholders' perceptions, highlighting that the change in land use had varied implications for, and were perceived differently by, different stakeholders. Farmworkers emphasized changes in social structures that weakened community bonds and erased valued connections to the land. At the same time, they increased employment of women, skills development, and increased wages as benefits of the new game farming regime. Landowners, on the other hand, indicated financial gains from the land use change. The transition therefore resulted in trade-offs that surfaced as social, economic, and cultural losses and gains. These changes, especially in social relationships and community structures, have implications for resilience and possible future pathways of development in the region.

Ecologists have long studied patterns, directions and tempos of change, but there is a pressing need to extend current understanding to empirical observations of abrupt changes as climate warming accelerates. Abrupt changes in ecological systems (ACES)-changes that are fast in time or fast relative to their drivers-are ubiquitous and increasing in frequency. Powerful theoretical frameworks exist, yet applications in real-world landscapes to detect, explain and anticipate ACES have lagged. We highlight five insights emerging from empirical studies of ACES across diverse ecosystems: (i) ecological systems show ACES in some dimensions but not others; (ii) climate extremes may be more important than mean climate in generating ACES; (iii) interactions among multiple drivers often produce ACES; (iv) contingencies, such as ecological memory, frequency and sequence of disturbances, and spatial context are important; and (v) tipping points are often (but not always) associated with ACES. We suggest research priorities to advance understanding of ACES in the face of climate change. Progress in understanding ACES requires strong integration of scientific approaches (theory, observations, experiments and process-based models) and high-quality empirical data drawn from a diverse array of ecosystems. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Globally, grasslands are shaped by grazing and fire, and grassland plants are adapted to these disturbances. However, temperate grasslands have been hotspots of land‐use change, and how such changes affect interrelations between herbivory, fire and vegetation are poorly understood. Such land‐use changes are widespread on the Eurasian steppe, where the dissolution of the Soviet Union in 1991 triggered the abandonment of cropland and pasture on globally relevant scales. Thus, to determine how relationships between plant functional composition, grazing and fire patterns changed after the Soviet Union dissolved, we studied a 358,000 km2 region in the dry steppe of Kazakhstan, combining a large field dataset on plant functional traits with multi‐scale satellite data. We found that increases in burned area corresponded to decreases in livestock grazing across large areas. Furthermore, fires occurred more often with high cover of grasses with high leaf dry matter content and thus higher flammability, whereas higher grazing pressure favoured grazing‐tolerant woody forbs and ruderal plants with high specific leaf area. The current situation of low grazing pressure represents a historically exceptional, potentially non‐analogue state. We suggest that the dissolution of the Soviet Union caused the disturbance regime to shift from grazer to fire control. As grazing and fire each result in different plant functional compositions, we propose that this led to widespread increases in grasses and associated changes in steppe plant community structure. These changes have potentially occurred across an area of more than 2 million km2, representing much of the world's largest temperate grassland area, with globally relevant, yet poorly understood implications for biodiversity and ecosystem functions such as carbon cycling. Additionally, future steppe management must also consider positive implications of abandonment (‘rewilding’) because reverting the regime shift in disturbance and as, Volkswagen Foundation http://dx.doi.org/10.13039/501100001663, Peer Reviewed

Globally, many shallow lakes have shifted from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state due to eutrophication. Such shifts are often accompanied by toxic cyanobacterial blooms, with specialized traits including buoyancy regulation and nitrogen fixation. Previous work has focused on how these traits contribute to cyanobacterial competitiveness. Yet, little is known on how these traits affect the value of nutrient loading thresholds of shallow lakes. These thresholds are defined as the nutrient loading at which lakes shift water quality state. Here, we used a modelling approach to estimate the effects of traits on nutrient loading thresholds. We incorporated cyanobacterial traits in the process-based ecosystem model PCLake+, known for its ability to determine nutrient loading thresholds. Four scenarios were simulated, including cyanobacteria without traits, with buoyancy regulation, with nitrogen fixation, and with both traits. Nutrient loading thresholds were obtained under N-limited, P-limited, and colimited conditions. Results show that cyanobacterial traits can impede lake restoration actions aimed at removing cyanobacterial blooms via nutrient loading reduction. However, these traits hardly affect the nutrient loading thresholds for clear lakes experiencing eutrophication. Our results provide references for nutrient loading thresholds and draw attention to cyanobacterial traits during the remediation of eutrophic water bodies.

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(2), (2020): e2019JC015700, doi:10.1029/2019JC015700., The formation mechanism as well as its temporal change of the North Pacific subtropical mode water (NPSTMW) is investigated using a 50‐year (1960–2009) ocean general circulation model hindcast. The volume budget analysis suggests that the formation of the NPSTMW is mainly controlled by the air‐sea interaction and ocean dynamics, but there is a regime shift of the relative importance between the two around late‐1980s. While the local air‐sea interaction process is a main driver of the NPSTMW formation prior to late‐1980s, ocean dynamics including the vertical entrainment become dominant since then. The NPSTMW formation is affected by the North Pacific Oscillation simultaneously in the early period, but with a few years lag in the later period. The interdecadal change of the driving mechanism of the interannual variability of the NPSTMW is probably due to the stronger (weaker) influence of local atmospheric forcing in the western North Pacific and unfavorable (favorable) wind stress curl condition for the remote oceanic forcing from the central North Pacific during the former (later) period. This regime shift may be related to the change of centers of the actions of the wind stress curl since the late‐1980s., The CORE2 data set was obtained from https://data1.gfdl.noaa.gov/nomads/forms/core/COREv2.html. The World Ocean Atlas 2009 and the Polar Hydrographic Climatology data set were obtained from https://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html and http://psc.apl.washington.edu/nonwp_projects/PHC/Climatology.html, respectively. The OSCAR data were taken from https://podaac.jpl.nasa.gov/dataset/OSCAR_L4_OC_third‐deg. The database of mixed layer depth is downloaded from http://mixedlayer.ucsd.edu. The data set of the Argo floats was taken from http://uskess.whoi.edu/. The sea surface height data observed by the satellite are available from AVISO (http://www.aviso.altimetry.fr/duacs/). The EN4 data set was downloaded from https://www.metoffice.gov.uk/hadobs/en4/. This study was supported by the National Research Foundation of Korea (NRF) Grant NRF‐2009‐C1AAA001‐0093, funded by the Korea government (MEST). The numerical simulation in this paper was supported by the Supercomputing Center of Korea Institute of Science and Technology Information (KISTI), with its supercomputing resources and technical support (KSC‐2018‐CRE‐0117). Y.‐O. Kwon was funded by National Science Foundation (NSF) EaSM2 OCE‐1242989. Y. H. Kim was partly supported by research projects entitled “Investigation and prediction system development of marine heatwave around the Korean Peninsula originated from the subarctic and western Pacific” (20190344) funded by the Ministry of Oceans and Fisheries (MOF). G. Pak was supported by in‐house projects of the Korea Institute of Ocean Science & Technology (PE99711, PE99811)., 2020-09-07

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(2), (2020): e2019JC015700, doi:10.1029/2019JC015700., The formation mechanism as well as its temporal change of the North Pacific subtropical mode water (NPSTMW) is investigated using a 50‐year (1960–2009) ocean general circulation model hindcast. The volume budget analysis suggests that the formation of the NPSTMW is mainly controlled by the air‐sea interaction and ocean dynamics, but there is a regime shift of the relative importance between the two around late‐1980s. While the local air‐sea interaction process is a main driver of the NPSTMW formation prior to late‐1980s, ocean dynamics including the vertical entrainment become dominant since then. The NPSTMW formation is affected by the North Pacific Oscillation simultaneously in the early period, but with a few years lag in the later period. The interdecadal change of the driving mechanism of the interannual variability of the NPSTMW is probably due to the stronger (weaker) influence of local atmospheric forcing in the western North Pacific and unfavorable (favorable) wind stress curl condition for the remote oceanic forcing from the central North Pacific during the former (later) period. This regime shift may be related to the change of centers of the actions of the wind stress curl since the late‐1980s., The CORE2 data set was obtained from https://data1.gfdl.noaa.gov/nomads/forms/core/COREv2.html. The World Ocean Atlas 2009 and the Polar Hydrographic Climatology data set were obtained from https://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html and http://psc.apl.washington.edu/nonwp_projects/PHC/Climatology.html, respectively. The OSCAR data were taken from https://podaac.jpl.nasa.gov/dataset/OSCAR_L4_OC_third‐deg. The database of mixed layer depth is downloaded from http://mixedlayer.ucsd.edu. The data set of the Argo floats was taken from http://uskess.whoi.edu/. The sea surface height data observed by the satellite are available from AVISO (http://www.aviso.altimetry.fr/duacs/). The EN4 data set was downloaded from https://www.metoffice.gov.uk/hadobs/en4/. This study was supported by the National Research Foundation of Korea (NRF) Grant NRF‐2009‐C1AAA001‐0093, funded by the Korea government (MEST). The numerical simulation in this paper was supported by the Supercomputing Center of Korea Institute of Science and Technology Information (KISTI), with its supercomputing resources and technical support (KSC‐2018‐CRE‐0117). Y.‐O. Kwon was funded by National Science Foundation (NSF) EaSM2 OCE‐1242989. Y. H. Kim was partly supported by research projects entitled “Investigation and prediction system development of marine heatwave around the Korean Peninsula originated from the subarctic and western Pacific” (20190344) funded by the Ministry of Oceans and Fisheries (MOF). G. Pak was supported by in‐house projects of the Korea Institute of Ocean Science & Technology (PE99711, PE99811)., 2020-09-07

Using historical in situ data sets, we investigated long-term variations in summer surface salinity and dissolved inorganic nitrogen concentration (DIN) in the northern East China Sea (ECS). From 1950 to 2002, there were interannual and decadal variations in sea surface salinity, as well as a long-term decrease. Along with the Changjiang discharge, wind fields and surface circulations appeared to play roles in determining the interannual salinity variation. Although we attributed the long-term decrease in surface salinity to a long-term increase in the Changjiang discharge, the high salinity between 1978 and 1988 appeared to be associated with an increase in the Kuroshio Current transport. The increase in DIN from 1971 to 2001 appeared to be caused by a combination of changes in Changjiang discharge and an increase in nitrogen fertilizer use in China. The long-term increase in DIN modified the nutrient composition, implying that biological production in the northern ECS changed from a DIN-limiting to a phosphorous-limiting. We should pay attention to changes in the northern ECS ecosystem in future decades because the volume of the Changjiang discharge, as well as its physical and chemical properties, may change dramatically because of the continuous anthropogenic perturbations and climate change., identifier:Journal of Geophysical Research, 113(C10), C10030; 2008