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The oceans are changing more rapidly than ever before. Unprecedented climatic variability is interacting with unmistakable long‐term trends, all against a backdrop of intensifying human activities. What remains unclear, however, is how to evaluate whether conditions have changed sufficiently to provoke major responses of species, habitats, and communities. We developed a framework based on multimodel inference to define ecosystem‐based thresholds for human and environmental pressures in the California Current marine ecosystem. To demonstrate how to apply the framework, we explored two decades of data using gradient forest and generalized additive model analyses, screening for nonlinearities and potential threshold responses of ecosystem states (n = 9) across environmental (n = 6) and human (n = 10) pressures. These analyses identified the existence of threshold responses of five ecosystem states to four environmental and two human pressures. Both methods agreed on threshold relationships in two cases: (1) the winter copepod anomaly and habitat modification, and (2) sea lion pup production and the summer mode of the Pacific Decadal Oscillation (PDO). Considered collectively, however, these alternative analytical approaches imply that as many as five of the nine ecosystem states may exhibit threshold changes in response to negative PDO values in the summer (copepods, scavengers, groundfish, and marine mammals). This result is consistent with the idea that the influence of the PDO extends across multiple trophic levels, but extends current knowledge by defining the nonlinear nature of these responses. This research provides a new way to interpret changes in the intensities of human and environmental pressures as they relate to the ecological integrity of the California Current ecosystem. These insights can be used to make more informed assessments of when and under what conditions intervention, preparation, and mitigation may enhance progress toward ecosystem‐based management goals.

Coral reefs in the western Atlantic and Caribbean are deteriorating primarily from disease outbreaks, increasing seawater temperatures, and stress due to land-based sources of pollutants including sediments associated with land use and dredging. Sediments affect corals in numerous ways including smothering, abrasion, shading, and inhibition of coral recruitment. Sediment delivery resulting in deposition and water quality deterioration can cause degradation at the spatial scale of corals or entire reefs. We still lack rigorous long-term studies of coral cover and community composition before, during and after major sediment stress, and evidence of recovery after watershed management actions. Here we present an overview of the effects of terrestrial sediments on corals and coral reefs, with recent advances in approaches to watershed assessment relevant to the delivery of sediments to these ecosystems. We present case studies of northeastern Caribbean watersheds to illustrate challenges and possible solutions and to draw conclusions about the current state of knowledge of sediment effects on coral reefs. With a better understanding of erosion and the pathways of sediment discharge to nearshore reefs, there is the increased potential for management interventions.

This paper focuses on the analysis and evaluation of resilience anchored in an economic perspective. Resilience, as well as most of the benefits provided by ecosystems, is not priced on current markets. However, this does not mean that resilience is of no value for humans. On the contrary, the interest of using an economic perspective, and the respective scientific methodology, will be put forward in terms of resilience relevance for ecosystem functioning, and its impact on human welfare. The economic perspective is anchored in an anthropocentric analysis evaluating resilience in terms of provision of natural capital benefits. These in turn are interpreted as insurance against the risk of ecosystem malfunctioning and the consequent interruption of the provision of goods and services to humans. For this analysis, we make use of a conceptual framework that identifies and describes the different value components of resilience. Finally, we present an illustration that discusses the economic analysis of resilience benefits in the context of the Venice Lagoon.

We are concerned with the management of ecological and economic systems with threshold responses and with several time scales. Although optimal control of such systems is seldom attainable, the form of such optimal controls provides important insights for more practical schemes. Here we optimize the expected discounted net benefits of phosphorus (P) loadings for a potentially eutrophic lake. The benefits accrue to agricultural interests from activities that result in loading, and costs accrue to other interests from the resulting deterioration of water quality. We extend the 1999 results of S. R. Carpenter, D. Ludwig, and W. A. Brock to account for dependence of P recycling upon the concentration of P in sediments. We obtain optimal policies using methods of dynamic programming with two state variables. We find a strong interaction between economic and ecological parameters in determining the optimal policy: the economic discount rate determines whether the time horizon is long or short, and this in turn strongly influences the magnitude of the optimal loadings. Simple policies that neglect dynamics of P in the sediments are inadequate unless the time horizon is short and the dynamics are slow. A stochastic model is essential if there are substantial random fluctuations in loadings. Uncertainty in the determination of the critical P density that triggers recycling cannot be neglected. Our results may be interpreted as a quantitative precautionary principle that takes account of both economic and ecological aspects of the management of the lake. Our results may also be used to illustrate economic ideas such as sustainable development, natural capital, option values, and income.

As global climate change and anthropogenic activities amplify widespread environmental variability, there is a strong need for management strategies that incorporate relationships between ecosystem components. This need is especially apparent when changes in environmental drivers cause threshold responses (abrupt, nonlinear changes) in ecosystems. Such ecological thresholds can provide useful reference points for management decisions. However, methods for detecting thresholds in empirical datasets may fail to find an existing threshold, find one that does not exist, or be biased in their estimates of threshold locations. These types of threshold misspecifications can result in high conservation and socioeconomic costs. Simulation studies can mitigate these risks by providing information about method performance across different scenarios. Here, we constructed a series of simulations to evaluate the robustness of threshold detection with generalized additive models (GAMs) when exposed to a variety of common, real‐world data characteristics. GAMs generally performed best when time series were long, observation error was low, thresholds were crossed fairly frequently, and covariates were accounted for. Over realistic ranges of values, observation error and frequency of threshold crossing had stronger effects on threshold detectability than time series length. Importantly, detectability was found to depend on both the shape of the threshold relationship and the statistical definition of the threshold location. As a case study, we applied this threshold detection method to an empirical dataset relating ocean temperature and the spatial distribution of Pacific hake (Merluccius productus), the largest volume fishery on the US West Coast. While the data suggest no statistical evidence for a threshold relationship, our simulations indicated approximately equal chances of true and false threshold detection given currently available data. Our results provide general guidelines for where threshold detection with GAMs is likely to be robust and are useful in the context of indicator development for ecosystem‐based management in a variable world.

Critical loads are a potentially important tool for protecting ecosystems from atmospheric deposition and for promoting recovery. Exceeding critical loads for nitrogen and sulfur can cause ecosystem acidification, nitrogen saturation, and biotic community changes. Critical loads are widely used to set policy for resource protection in Europe and Canada, yet the United States has no similar national strategy. We believe that ecosystem science and resource protection policies are sufficiently advanced in the United States to establish critical loads for federal lands. Communication and interaction between federal area managers and scientists will ensure that critical loads are useful for assessing ecosystem conditions, influencing land management decisions, and informing the public about the status of natural resources. Critical loads may also be used to inform air pollution policy in the United States, regardless of whether critical loads are directly linked to air quality regulations and emissions reductions agreements, as they are in Europe.

Droughts have increased globally in the twenty-first century and are expected to become more extreme and widespread in the future. Assessments of how drought affects plants and ecosystems lack consistency in scope and methodology, confounding efforts to mechanistically interpret structural and functional impacts and predict future transformations under climate change. To promote integration among studies, we identify water deficit conditions that are ecologically meaningful, clarify the stages in which ecological drought progresses, and consider approaches to synthesize drought effects across multiple species and ecosystems. This improved ecological drought framework reveals advantages of using different ecological drought metrics and strengthens approaches to distinguish ecosystem stress from crossing an irreversible threshold. We employ several well-studied examples from water-limited ecosystems, which contain plants that are often at their physiological limits and highly responsive to climate variability. We suggest that emerging research on early warning signs, drought recovery, and the effects of land management interventions be incorporated into the ecological drought framework. An integrative approach to understand ecological drought can accelerate scientific advancement and create opportunity to adapt and prepare for crossing irreversible ecosystem thresholds.

Climate change and aquaculture influence the blue carbon storage in aquatic ecosystems but accurate projections of their separate impacts are difficult owing to the multiplicity of pathways involved. Because of aquaculture's growing contribution to seafood supply, society will find it difficult to impose serious restrictions at a time when fisheries are challenged by changes in the ecosystem caused by climate change. The effect of aquaculture on the ability of coastal vegetation such as seagrass meadows to sequester and store carbon is determined by the type of aquaculture. It is understood that compared to finfish aquaculture, the shellfish aquaculture is generally benign with no significant impact on ecosystem eutrophication, at least on a short‐term basis. There are knowledge gaps when it comes to mechanisms that influence blue carbon stocks and more empirical studies are needed to provide accurate assessments. With an ecosystem approach to marine resources and aquaculture management gaining ground, it is evident that the focus will be on a holistic management of activities within the limits of ecosystem thresholds. In this context, investigations are required on nutrient and organic subsidies to coastal marine ecosystems, especially the blue carbon resources. It should also be established whether the ecosystem behaves as a dynamic non‐point attractor or point attractor and what influence changes in parameters (light attenuation between the plant communities, mineralized limiting nutrient supply, CO 2 supply, pH and temperature) exert of the whole dynamic. The data need to be interpreted under the umbrella of the particular ecosystem's long‐term dynamics with the knowledge of the quality of external organic subsidies.

Pacific salmon influence temperate terrestrial and freshwater ecosystems through the dispersal of marine-derived nutrients and ecosystem engineering of stream beds when spawning. They also support large fisheries, particularly along the west coast of North America. We provide a comprehensive synthesis of relationships between the densities of Pacific salmon and terrestrial and aquatic ecosystems, summarize the direction, shape, and magnitude of these relationships, and identify possible ecosystem-based management indicators and benchmarks. We found 31 studies that provided 172 relationships between salmon density (or salmon abundance) and species abundance, species diversity, food provisioning, individual growth, concentration of marine-derived isotopes, nutrient enhancement, phenology, and several other ecological responses. The most common published relationship was between salmon density and marine-derived isotopes (40%), whereas very few relationships quantified ecosystem-level responses (5%). Only 13% of all relationships tended to reach an asymptote (i.e., a saturating response) as salmon densities increased. The number of salmon killed by bears and the change in biomass of different stream invertebrate taxa between spawning and nonspawning seasons were relationships that usually reached saturation. Approximately 46% of all relationships were best described with linear or curved nonasymptotic models, indicating a lack of saturation. In contrast, 41% of data sets showed no relationship with salmon density or abundance, including many of the relationships with stream invertebrate and biofilm biomass density, marine-derived isotope concentrations, or vegetation density. Bears required the highest densities of salmon to reach their maximum observed food consumption (i.e., 9.2 kg/m² to reach the 90% threshold of the relationship’s asymptote), followed by freshwater fish abundance (90% threshold = 7.3 kg/m² of salmon). Although the effects of salmon density on ecosystems are highly varied, it appears that several of these relationships, such as bear food consumption, could be used to develop indicators and benchmarks for ecosystem-based fisheries management.