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We are already experiencing the rapid pace of environmental perturbation in the Anthropocene, necessitating the development of new tools and techniques for measuring changes in ecosystem dynamics. Sentinel species, from birds to invertebrates, have been used to provide insights into ecosystem function, as leading indicators of risk to human health and as harbingers of future change, with implications for ecosystem structure and function. Here, we offer an update to previous research identifying marine top predators as indicators of ecosystem shifts and examine terrestrial sentinels and the latest research on sentinels of pollution and human health. Using ecosystem sentinels enables rapid response and adaptation to ecosystem variability and environmental change in part because they may be easier to observe and in part because they may serve as leading indicators of ecosystem disruption. While there may not be a given taxon that is best suited as sentinels, we highlight how to select the most effective sentinels, including examples of when sentinel species have been incorporated into management. Choosing a suite of appropriate sentinels both will give insight into ecosystem processes and can help manage changing ecosystems into the future. [ABSTRACT FROM AUTHOR]

Forage fishes are key energy conduits that transfer primary and secondary productivity to higher trophic levels. As novel environmental conditions caused by climate change alter ecosystems and predator-prey dynamics, there is a critical need to understand how forage fish control bottom-up forcing of food web dynamics. In the northeast Pacific, northern anchovy (Engraulis mordax) is an important forage species with high interannual variability in population size that subsequently impacts the foraging and reproductive ecology of marine predators. Anchovy habitat suitability from a species distribution model (SDM) was assessed as an indicator of the diet, distribution and reproduction of four predator species. Across 22 years (1998-2019), this anchovy ecosystem indicator (AEI) was significantly positively correlated with diet composition of all species and the distribution of common murres (Uria aalge), Brandts cormorants (Phalacrocorax penicillatus) and California sea lions (Zalophus californianus), but not rhinoceros auklets (Cerorhinca monocerata). The capacity for the AEI to explain variability in predator reproduction varied by species but was strongest with cormorants and sea lions. The AEI demonstrates the utility of forage SDMs in creating ecosystem indicators to guide ecosystem-based management.

The 2014–2016 Northeast Pacific marine heatwave (MHW) induced the warmest 3‐year period on record in the California Current Ecosystem. We tested whether larval fish assemblage structure, phenology, and diversity dynamics were comparable to past warming events from 1951 to 2013. First, we hypothesized, based on past observations of biological effect of warming, that mesopelagic species with southern distributions relative to southern California and Pacific sardine Sardinops sagax (a coastal pelagic species) would increase during the MHW while northern mesopelagics and northern anchovy Engraulis mordax (coastal pelagic) abundances would decline. Similar to past warming, southern mesopelagics increased and northern mesopelagics decreased. Unexpectedly, however, a common southern mesopelagic, Mexican lampfish Triphoturus mexicanus, was approximately three times more abundant than the previous annual high. Furthermore, whereas sardine abundance did not increase, larval anchovy abundance rose to near‐record highs in summer 2016. Second, we hypothesized that fishes would spawn earlier during the MHW. Fishes did not spawn in an earlier season within a year, but five of six southern mesopelagic taxa spawned earlier than typical within winter and spring. Third, we predicted that species richness would increase moderately due to an influx of southern and exodus of northern species. Richness, however, was very high in all seasons and the highest ever during the summer as multiple species with primarily southern distributions were recorded spawning for the first time in southern California. The richness of northern species was also unexpectedly high during the MHW. Northern species likely persisted in the study area because in addition to the warm water, pockets of cold water were consistently present. If, as predicted, conditions similar to the MHW become more common as oceans warm, this unique and largely unexpected combination of fishes may reflect future biological conditions. [ABSTRACT FROM AUTHOR]

With accelerating climate variability and change, novel approaches are needed to warn managers of changing ecosystem state and to identify appropriate management actions. One strategy is using indicator species—like seabirds as ecosystem sentinels—to monitor changes in marine environments. Here, we explore the utility of western gulls (Larus occidentalis) breeding on Southeast Farallon Island as a proxy of ecosystem state in coastal California by investigating the interannual variability in gull foraging behavior from 2013 to 2019 in relation to upwelling conditions, prey abundances, and overlap with humpback whales (Megaptera novaeangliae) as gulls frequently feed in association with whales. Western gulls have a flexible diet and forage on land and at-sea. We combined gull GPS tracking data during the incubation phase, ecosystem survey data on multiple predator and prey species, and derived oceanographic upwelling products. When foraging at sea, gulls overlapped with cool upwelled waters. During 2015–2017, 25% more gull foraging trips visited land than in other years, where land trips were on average ∼8 h longer and 40% further than sea trips, which coincided with high compression of coastally upwelled waters (habitat compression) in 2015–2016. Gull foraging behavior was related to local prey abundances, where more foraging occurred near shore or on land when prey abundances were low. However, visual surveys indicated that ∼70% of humpback whale observations co-occurred with gulls, and the year with the most foraging on land (2017) corresponded to regionally low relative whale abundances, suggesting gull movement patterns could be an indicator of whale presence. Further, both whales and gulls forage near-shore under high upwelling habitat compression and low krill abundance. Hence, the deployment of year-round tags on gulls with the capability of near real-time data accessibility could provide important fine-scale metrics for conservation and management of the threatened yet recovering eastern Pacific humpback whale population between infrequent and coarse surveys. Entanglement in fishing gear and ship strikes are major inhibitors to whale recovery and have increased concomitantly with human use of ocean resources. Moreover, as climate variability and change increase, novel indicators should be explored and implemented to inform marine spatial planning and protect species across multiple scales from new risks.

This study incorporated two pathways of environmental forcing (i.e. "larval mortality forcing" and "somatic growth forcing") into an end-to-end ecosystem model (Object-oriented Simulator of Marine ecOSystEms, OSMOSE) developed for the Pacific North Coast Integrated Management Area (PNCIMA) off western Canada, in order to evaluate alternative fisheries management strategies under environmental changes. With a suite of ecosystem-level indicators, the present study first compared the ecosystem effects of different pathways of environmental forcing scenarios; and then evaluated the alternative fisheries management strategies which encompassed a series of fishing mortality rates relative to F MSY (the fishing mortality rate that produces maximum sustainable yield) and a set of precautionary harvest control rules (HCRs). The main objectives of this study were to (i) explore the ecosystem effects of different environmental forcing scenarios; (ii) identify the impacts of different fishing mortality rates on marine ecosystem structure and function; and (iii) evaluate the ecosystem-level performance of various levels of precautionary HCRs. Results indicated that different pathways of environmental forcing had different ecosystem effects and incorporating appropriate HCRs in the fisheries management process could help maintain ecosystem health and sustainable fisheries. This study provides important information on future fisheries management options within similar marine ecosystems that are facing global changes. [ABSTRACT FROM AUTHOR]

Many threatened fish species that utilize riverine habitats are faced with habitat degradation and subsequent deterioration in their ecological surroundings. Habitat degradation is a consequence of water quality parameters associated with anthropogenic activities including mining, industrial, agricultural and urban activities. We examined how the movement behaviour of radio-tracked Orange-Vaal largemouth yellowfish (Labeobarbus kimberleyensis) responded to a suite of water quality chemical parameters and habitat features in the Vaal River, South Africa. We found that the probability of their movement increased with a decrease in water clarity, presence of emergent and overhanging marginal vegetation and fast flowing rapids. High mobility in conditions of low water clarity was probably related to low prey capture success of this piscivorous fish. High movement of largemouth yellowfish in emergent and overhanging marginal vegetation areas and rapid habitat biotopes were attributed to accessibility of prey within these important cover features. When water quality parameters were considered, the probability of largemouth yellowfish movement increased with increasing levels of dissolved chloride (Cl) and silicon (Si), whereas movement decreased with high phosphate (PO4) concentrations and increased with alkalinity levels in the river. High nutrient levels associated with eutrophication caused reductions in the movement of largemouth yellowfish. The association of increased movement of largemouth yellowfish with increasing Cl and Si is indicative of degraded habitat condition in the Vaal River system. Our study showed the importance of monitoring fish behavioural movement patterns to multiple environmental parameters, as these fish are important ecological indicators when appropriate conservation and management plans of freshwater ecosystems are required. [ABSTRACT FROM AUTHOR]

Abstract 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.

Forage fishes are key energy conduits that transfer primary and secondary productivity to higher trophic levels. As novel environmental conditions caused by climate change alter ecosystems and predator-prey dynamics, there is a critical need to understand how forage fish control bottom-up forcing of food web dynamics. In the northeast Pacific, northern anchovy ( Engraulis mordax ) is an important forage species with high interannual variability in population size that subsequently impacts the foraging and reproductive ecology of marine predators. Anchovy habitat suitability from a species distribution model (SDM) was assessed as an indicator of the diet, distribution and reproduction of four predator species. Across 22 years (1998-2019), this anchovy ecosystem indicator (AEI) was significantly positively correlated with diet composition of all species and the distribution of common murres ( Uria aalge ), Brandt's cormorants ( Phalacrocorax penicillatus ) and California sea lions ( Zalophus californianus ), but not rhinoceros auklets ( Cerorhinca monocerata ). The capacity for the AEI to explain variability in predator reproduction varied by species but was strongest with cormorants and sea lions. The AEI demonstrates the utility of forage SDMs in creating ecosystem indicators to guide ecosystem-based management.

The conversion of wetlands and its associated habitat for farming, residential development and commercial purposes has led to many small disconnected patches of native vegetation surrounded by generally inhospitable human altered land uses. Such human interventions pose a serious threat to the survival of wetland dependent indicator species such as the serval ( Leptailurus serval ) in the Drakensberg Midlands of KwaZulu-Natal, South Africa. To address the effects of habitat fragmentation on serval space use we used GPS fixes of collared individuals for 100 days between May 2013 and January 2014. We tracked five females and eleven male servals with GPS-UHF collars. Fragmentation indices at the class level (wetland, forest with bushland, grassland and cropland) were measured within the collared serval's minimum convex polygon area (MCP) of home range. Serval use points and fragmentation indices were extracted to each sub-landscape unit of 2 km 2 falling within the MCP home range. The response of serval population to fragmentation indices was analyzed using generalized linear models at three levels: male, female and the overall population. We found that core area of wetland positively explained landscape use by servals. Effects of forest core area, forest proximity and patch richness were important for landscape use by male servals. Male and female serval use declined with increase in complex shapes of forest and grassland, wetland clumpiness for females and overall, and cropland patches for servals overall. Our results showed that wetland is a key determinant for the survival of male and female servals in fragmented landscapes therefore effective conservation of serval population demands adequate viable native habitat. [ABSTRACT FROM AUTHOR]

Yellow-eyed penguins (hoiho,Megadyptes antipodes) are a Nationally Vulnerable species, restricted in distribution to the lower South Island, Stewart Island/Rakiura, and the New Zealand sub-Antarctic islands. The foraging behaviour of penguins is considered an indicator of marine ecosystems because when breeding they rely on the availability of prey close to their nests. Time–depth recorders were attached to eight nesting hoiho at Port Pegasus/Pikihatiti, Stewart Island. While at sea, hoiho spent 55% of their time diving in water > 3 m deep. Their mean dive depth was 61 ± 6.1 m with mean dive duration 2 ± 0.1 min. Based on bathymetric charts, hoiho could undertake these dives < 10 km from their nesting sites. There was significant variability in hoiho foraging behaviour within New Zealand depending on bathymetry and anthropogenic impacts. Understanding hoiho foraging behaviours could help to determine to what extent they impact on this species' life history and its role as an ecosystem indicator. [ABSTRACT FROM PUBLISHER]

Beaches are landscapes valued greatly by society that, when left intact, support both ecological processes and sustainable use. In Southeast Florida, alteration of beaches for human activities has resulted in substantial loss of naturally functioning beach habitat and reduced biological diversity. Of particular importance is the impact on beach ecosystems by the nearby urban environment. Beaches are dynamic ecosystems that require space to respond to natural or anthropogenic drivers and pressures. In Southeast Florida urban development has restricted or eliminated the ability of most beaches to react in a manner that conserves the natural beach ecosystem. The frequent result has been oceanfront areas with little or no intact habitat and limited opportunities for restoration, though disturbed beaches may still provide opportunities for ocean access, recreation, and other socioeconomic benefits in highly urbanized areas. In this study we present a framework for selecting relevant ecosystem and human dimension indicators for the beaches of Southeast Florida based on a conceptual ecosystem model. To capture the level of beach disturbance relatively pristine beaches and heavily altered beaches are endpoints in a continuum of beach development. Across this continuum nine indicators were developed to quantify beach condition. For ecosystem and human dimension assessment purposes, beaches were placed in one of two overarching categories: undeveloped to relatively undeveloped, or developed to highly developed. Nine selected indicators are then assessed as good (3), fair (2), or poor (1). The indicator scores are then summed to produce a total condition score for a particular beach. This simple 'stop-light' method is applicable even when there are limited data and provides a useful relative determination of ecosystem condition. Case studies employing this methodology are presented for three Southeast Florida beaches ranging from mostly natural to highly developed condition. The indicators directly address both ecosystem and human dimension goals to maintain healthy, sustainable, and useable beaches and shorelines in Southeast Florida. They balance the ecological benefit of remaining natural beaches with the societal benefit of recreational opportunities and access for a beach that can no longer sustain a suitable ecosystem. Each indicator is interpreted in the context of the trade-offs among multiple ecosystem and human dimension services provided by most beaches in Southeast Florida. [ABSTRACT FROM AUTHOR]

Ecosystem-based management (EBM) has emerged as a basic approach for managing human activities in marine ecosystems, with the aim of recovering and conserving marine ecosystems and the services they deliver. Integrated ecosystem assessments (IEAs) further the transition of EBM from principle to practice by providing an efficient, transparent means of summarizing the status of ecosystem components, screening and prioritizing potential risks, and evaluating alternative management strategies against a backdrop of environmental variability. In this paper, we draw upon lessons learned from the US National Oceanic and Atmospheric Administration's IEA programme to outline steps required for IEA implementation. We provide an overview of the conceptual framework for IEAs, the practical constraints that shape the structure of individual IEAs, and the uses and outcomes of IEAs in support of EBM. [ABSTRACT FROM PUBLISHER]

Probst, W. N., Stelzenmüller, V., and Fock, H. 2012. Using cross-correlations to assess the relationship between time-lagged pressure and state indicators: an exemplary analysis of North Sea fish population indicators. – ICES Journal of Marine Science, 69: 670–681.A sustainable ecosystem-based management, as postulated by the European Union-Marine Strategy Framework Directive (MSFD), requires a sound understanding of the cause–effect relationships between human pressures and ecosystem states. In this study, cross-correlations are used to introduce a protocol for the analysis of time-lagged relationships between pressure and state indicators. To perform meaningful cross-correlations, the time-series of the pressure and the state indicator should be prewhitened by fitting autoregressive integrated moving average models to the pressure indicator time-series. This study provides some theoretical examples on the implications of non-prewhitened and prewhitened cross-correlations and exemplifies the use of prewhitened cross-correlations to compare the pressure–state relationship of a well-established indicator suite vs. the relationship of a new indicator proposed under the MSFD. The established indicator suite is fishing mortality (F) vs. spawning-stock biomass (SSB), the new indicator suite is F vs. the 95% percentile of the length frequency distribution (L95). The L95 aims to characterize the proportion of large individuals within a population. The prewhitened cross-correlations for F and SSB are significant for all four analysed species (cod, haddock, saithe, and plaice), the L95 is correlated with F for cod, haddock, and saithe. However, the L95 was also influenced by the annual survey catch and recruitment. [ABSTRACT FROM PUBLISHER]

Abstract: The emerging science and policy arena of marine ecosystem-based management is beset with the challenging question of how to assess the urgency of problems influencing different ecosystem components. In this paper, we introduce a synthetic and efficient framework to identify land- or sea-based activities that pose the greatest risk to valued members of marine ecosystems, including mammals, fishes, and invertebrates. Ecosystem-based risk is scored along two axes of information: the exposure of a population to an activity, and the sensitivity of the population to that activity, given a particular level of exposure. Risk is illustrated in a variety of ways, including two-dimensional contour plots and maps showing regional variation in risk. We apply this risk assessment framework to regional populations of indicator species in Puget Sound, WA, USA. This case study provides insight into how risk varies for particular activity–species combinations, and, because it is applied to indicator species, it also provides an estimate of how different activities influence risk to overall ecosystem structure and function. More generally, the risk assessment approach highlights the linkages between land-based activities and risk to marine species and can be used to evaluate the potential impacts of a diversity of human activities on coastal oceans. The framework is scalable, transparent, and repeatable and can be used now to facilitate the implementation of ecosystem-based management, including integrated ecosystem assessments and coastal and marine spatial planning. [Copyright &y& Elsevier]

Assessing and monitoring the ecological integrity of terrestrial and aquatic ecosystems is a vital component of effective water resource management, sustainable land use planning, and biodiversity protection and management. Our objective was to quantify, evaluate and map measures of ecological condition and vulnerability for 32 sub-basins in South Carolina. Principal Component Analysis of 29 integrity measures identified six significant components that explained 78.5 percent of the variance in indicator values among watersheds. These components corresponded to indicators associated with urban development and human stressors, habitat extent and priority species occurrences, agricultural development and land protection, riparian land use and stream impairment, and agricultural conversion and abandonment. Composite measures of watershed integrity provided a simple means for prioritizing watersheds for potential management activities. The approach used in this study ultimately provides a flexible means for assessing broad-scale patterns of biotic integrity that can be tailored to highlight specific management needs or goals while facilitating the selection of a suite of complementary measures that effectively characterize system properties. [ABSTRACT FROM AUTHOR]

Gårdmark, A., Nielsen, A., Floeter, J., and Möllmann, C. 2011. Depleted marine fish stocks and ecosystem-based management: on the road to recovery, we need to be precautionary. – ICES Journal of Marine Science, 68: 212–220. Precautionary management for fish stocks in need of recovery requires that likely stock increases can be distinguished from model artefacts and that the uncertainty of stock status can be handled. Yet, ICES stock assessments are predominantly deterministic and many EC management plans are designed for deterministic advice. Using the eastern Baltic cod (Gadus morhua) stock as an example, we show how deterministic scientific advice can lead to illusive certainty of a rapid stock recovery and management decisions taken in unawareness of large uncertainties in stock status. By (i) performing sensitivity analyses of key assessment model assumptions, (ii) quantifying the uncertainty of the estimates due to data uncertainty, and (iii) developing alternative stock and ecosystem indicators, we demonstrate that estimates of recent fishing mortality and recruitment of this stock were highly uncertain and show that these uncertainties are crucial when combined with management plans based on fixed reference points of fishing mortality. We therefore call for fisheries management that does not neglect uncertainty. To this end, we outline a four-step approach to handle uncertainty of stock status in advice and management. We argue that it is time to use these four steps towards an ecosystem-based approach to fisheries management. [ABSTRACT FROM PUBLISHER]

Bundy, A., Shannon, L. J., Rochet, M-J., Neira, S., Shin, Y-J., Hill, L., and Aydin, K. 2010. The good(ish), the bad, and the ugly: a tripartite classification of ecosystem trends. – ICES Journal of Marine Science, 67: 745–768.Marine ecosystems have been exploited for a long time, growing increasingly vulnerable to collapse and irreversible change. How do we know when an ecosystem may be in danger? A measure of the status of individual stocks is only a partial gauge of its status, and does not include changes at the broader ecosystem level, to non-commercial species or to its structure or functioning. Six ecosystem indicators measuring trends over time were collated for 19 ecosystems, corresponding to four ecological attributes: resource potential, ecosystem structure and functioning, conservation of functional biodiversity, and ecosystem stability and resistance to perturbations. We explored the use of a decision-tree approach, a definition of initial ecosystem state (impacted or non-impacted), and the trends in the ecosystem indicators to classify the ecosystems into improving, stationary, and deteriorating. Ecosystem experts classified all ecosystems as impacted at the time of their initial state. Of these, 15 were diagnosed as “ugly”, because they had deteriorated from an already impacted state. Several also exhibited specific combinations of trends indicating “fishing down the foodweb”, reduction in size structure, reduction in diversity and stability, and changed productivity. The classification provides an initial evaluation for scientists, resource managers, stakeholders, and the general public of the concerning status of ecosystems globally. [ABSTRACT FROM PUBLISHER]

The article examines the effect of climate change in the phasing and amplitude of upwelling in the current marine ecosystems in California. It states that the effects could be strong during the spring or summer upwelling season, but may be influential during winter before the spring transition. It notes that winter proxies of upwelling were the most significant determinants of seabird reproductive phenology, with strong upwelling in January to March leading to earlier dates of egg-laying in such species.

Exergy, the thermodynamic function that represents the distance of an open system from equilibrium, is proposed as an ecological indicator for summarizing the complex dynamics occurring in a disturbed community during its recovery processes. These complex dynamics can be difficult to capture by using classical indices. In this study, we sampled macrobenthos using the BACI scheme (before versus after; control versus impact) in tidal wetlands of west Chongming Island, China, an area that has been disturbed by ecological engineering measures. Exergy storage is estimated for benthic communities. The control area is proposed as dynamic reference for estimating local exergy storage of the benthic community. Three different methods were used for estimating exergy on the basis of coefficients: (a) taken for taxa groups; (b) estimated from coding genes given for broad taxonomic groups; and (c) estimated from genome size taken as close as possible to the taxonomic level of the species, providing a basis for inferring similarities. We found a decrease of local exergy content in the disturbed area 9 days after the disturbance. Subsequently, the reference exergy of the benthic community increased (i.e. in the surrounding control area) in accordance with the proposed hypothesis regarding the dynamics of exergy storage during a system's development. Estimates of local exergy arrived at using the three methods provided comparable results. Based on this, we then discuss the feasibility of using the more readily available genome size data for estimating exergy. This result may have important implications for broader application of this indicator to biological systems. Moreover, the adjacent control samples seem to represent an appropriate dynamic reference for estimating the local exergy of disturbed communities. We found that exergy was a useful indicator that integrates the processes underlying the recovery of the benthic community after disturbance. [ABSTRACT FROM AUTHOR]

Abstract: The description of ecosystems’ evolution is a challenge for many scientists. Several attempts have been made, mostly using compartments and flows, to describe the structure of ecosystems and holistic indicators or goal functions (GF) to describe the state and the trend of their evolution. Under a steady flow of energy from the environment, an ecosystem can increase the biomass by enlarging the number of individuals and/or their body weights until a certain steady state level. In this situation neither the structure (e.g. species composition) nor the pattern of flows linking its compartments vary and both biomass and flow reach an “optimal” level. Benefits compensate the costs of the ecosystem evolution. A question is open: when can an ecosystem be considered to be in an optimal state and how does it reach this state? The answer to this question is also useful to solve the problems related to the concept of reference state as posed in the Water Framework Directive (WFD, EU, 2000/60/EC). In order to answer this question the characteristics of a suitable indicator are discussed and two state indicators are proposed, based on the assumption that costs and benefits of the ecosystem growth have to be in balance. The first one, the benefit/cost indicator (BC), is a function of well known state indicators, that fully satisfies the properties required although is difficult to compute and complex to understand. Nevertheless, from the researcher point of view, this indicator gives interesting insights into system behavior. The second, the supply demand balance (SDB), is an indicator based on two main assumptions, the first one being that an ecosystem can be represented by a network of compartments and flows, the second that the metabolic rates scale across species approximately as the (3/4) power of mass. The SDB indicator summarizes the distance of an ecosystem from an optimal state in a single number. Under these assumptions the SDB indicator can be regarded as a measure of ecosystem state. It is easy to compute and simple to understand. SDB looks like a good indicator both for scientific and practical uses to understand where the ecosystem is going. Finally the applicability of SDB is investigated by computing its values for 33 trophic networks describing the food webs of different aquatic ecosystems. [Copyright &y& Elsevier]

Few indicators exist that measure the effects of fishing at the whole-ecosystem level. A 4D ecosystem exploitation index is proposed that integrates four measures of ecosystem status: (i) the trophic balance of exploitation, (ii) the intensity of exploitation, (iii) species richness, and (iv) disturbance of the trophic structure. The central concept is that fisheries should extract yield in proportion to the productivity at each trophic level, at sustainable exploitation rates, with minimal disturbance to the trophic structure, and with no loss in species richness. The ecosystem exploitation index is tested on simulated ecosystem data and applied to data from the eastern Scotian Shelf, Canada. The model simulations provided consistent results that should facilitate cross-system comparisons of exploitation and ecosystem status. When applied to actual observations, the results were less coherent, likely attributable to lag effects and environmental impacts. All fisheries likely alter the trophic structure of ecosystems, and the rate and trophic pattern of exploitation determines the level of change. Exploiting all trophic levels equally would always result in less change to trophic structure than top-heavy exploitation. Further testing is required to determine lag effects and sensitivity to various assumptions. [Copyright &y& Elsevier]