Food Web Indicators Research Articles

Enhancing ecological complexity in soft‐bottom coastal ecosystems: the impact of introducing hard substrates

Coastal ecosystems globally face pressures, with natural coastal habitats being replaced by engineered structures. While hard structures for navigation‐purposes and coastal defense can negatively impact native communities, they can also be applied in ecological restoration as artificial reefs. This way substrates may facilitate establishment of biogenic (shellfish) reefs and provide habitat heterogeneity in soft‐sediment ecosystems. In a 1.5‐year experiment, we introduced six different types of natural or biodegradable hard substrates in a subtidal soft‐sediment system. We compared the substrates with surrounding soft sediment and evaluated differences among substrate types using biodiversity indices, community composition analyses, and food web indicators. This offers a comprehensive understanding of how the introduced hard substrates affect ecosystem complexity. Overall ecological complexity indicators were higher in the second year of the experiment. We found a significant increase in species richness, community composition, and link density (number of feeding interactions per species) on hard substrates compared to the surrounding sediment. However, Shannon diversity index and food web connectance (measure of food web saturation) did not differ between substrates and the surrounding sediment. Although differences among types of hard substrates were small, certain species were uniquely associated with specific substrates with wood and granite performing best. While there was no establishment of epibenthic shellfish reefs within 1.5 years, we conclude that introducing hard substrates effectively enhances ecological complexity in soft‐bottom coastal ecosystems within that timeframe. We recommend the use of substrates with a historical ecological relevance in the system for scaling up introduction of substrates for ecological restoration.

Spatial analysis of demersal food webs through integration of eDNA metabarcoding with fishing activities

The evaluation of the status of marine communities, and especially the monitoring of those heavily exploited by fisheries, is a key, challenging task in marine sciences. Fishing activities are a major source of disruption to marine food webs, both directly, by selectively removing components at specific trophic levels (TL), and indirectly, by altering habitats and production cycles. Food web analysis can be very useful in the context of an Ecosystem Approach to Fisheries, but food web reconstructions demand large and expensive data sets, which are typically available only for a small fraction of marine ecosystems. Recently, new technologies have been developed to easily, quickly and cost-effectively collect environmental DNA (eDNA) during fishing activities. By generating large, multi-marker metabarcoding data from eDNA samples obtained from commercial trawlers, it is possible to produce exhaustive taxonomic inventories for the exploited ecosystems, which are suitable for food-web reconstructions. Here, we integrate and re-analyse the data of a recent study in which the α diversity was investigated using the eDNA opportunistically collected during fishing operations. Indeed, we collect highly resolved information on species feeding relationships to reconstruct the food webs at different sites in the Strait of Sicily (Mediterranean Sea) from eDNA and catch data. After observing that the trophic networks obtained from eDNA metabarcoding data are more consistent with the available knowledge, a set of food web indicators (species richness, number of links, direct connectance and generality) is computed and analysed to unravel differences in food webs structure through different areas (spatial variations). Species richness, number of links and generality (positively) and direct connectance (negatively) are correlated with increasing distance from the coast and fishing effort intensity. The combined effects of environmental gradients and fishing effort on food web structure at different study sites are then examined and modelled. Taken together, these findings indicate the suitability of eDNA metabarcoding to assist and food web analysis, obtain several food web-related ecological indicators, and tease out the effect of fishing intensity from the environmental gradients of marine ecosystems.

Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model

The structure and functioning of the food web of the Francisco Coloane Marine Area in the Magellan Strait, Chile, was quantified, with an emphasis on identifying the ecological role of the squat lobster (Munida gregaria) and the Fuegian sprat (Sprattus fuegensis). Food web indicators, the trophic level, and centrality indices were estimated using Ecopath with Ecosim. Dynamic simulations were carried out to evaluate the ecosystem impacts of biomass changes in squat lobster and Fuegian sprat. The model calculated a total ecosystem biomass of 71.7 t km-2 and a total primary production of 2450.9 t km-2 year-1. Squat lobster and Fuegian sprat were located in specific trophic levels of 2.3 and 2.7, respectively. Squat lobster reduction produced a decrease in the biomass of red cod (42-56%) and humpback whales (25-28%) and Fuegian sprat reduction a decrease in penguins (15-37%) and seabirds (11-34%). The Francisco Coloane Area is an immature ecosystem with productivity and energy flows values within those reported for productive ecosystems; the role of the squat lobster seems to be related to the structure of the food web, and the role of the Fuegian sprat seems to be related to the functioning of the ecosystem and to the energy transfer to top predators.

Multifunctionality of soil food webs

Soil food webs regulate functioning, ensure stability and support biodiversity both below and above ground. Structure of feeding interactions in soil food webs is shaped by complex size and spatial organization of soil life, and diverse adaptations of soil-dwelling consumers. Strengths of the feeding interactions between consumers and their resources can be quantitatively expressed in ‘energy fluxes’, reflecting trophic functions such as herbivory, microbivory, or predation. Multiple energy fluxes support multiple trophic-related functions and thus support multiple functions at the ecosystem level. I will show how we can use traits of soil consumers to reconstruct network topology of soil food webs and quantify energy fluxes along their resource, size, and spatial dimensions (Potapov 2022). I will then introduce “trophic multifunctionality” i.e. simultaneous support of multiple trophic functions by the food web (analogous to ecosystem multifunctionality) as an approach to calculate a number of quantitative food-web indicators and compare them across systems. With further validation, trait and energy flux approaches would allow to embrace functioning of soil communities from microorganisms to large animals and in perspective use this knowledge to actively manage soil functioning.

Isotopic and traits-based trophic diversity of Canadian Beaufort Sea benthic communities in relation to food supply

In the Arctic, climate-driven alterations to the quality and quantity of organic matter reaching the seafloor will likely affect benthic food web function. We used biomass-weighted diversity measures based on trophic traits (those related to feeding behaviours, e.g., mobility, size, food source), stable isotope ratios (δ15N and δ13C), and taxonomy to assess linkages between benthic food web structure and indicators of food supply in the shelf and slope ecosystems of the Canadian Beaufort Sea and Amundsen Gulf (down to 500 m). Benthic communities across both regions used a similar diversity of sedimentary organic matter sources according to stable isotopes, despite known differences between regions in organic matter input and benthic–pelagic coupling. Shelf-edge and upper-slope communities exhibited relatively high trophic trait diversity, which likely reflected the exploitation of pulsed food inputs associated with dynamic processes at the shelf break that affect the production and advection of organic matter to the benthos. Pairwise relationships between trophic traits and sedimentary proxies of benthic food supply were not significant at the regional scale. However, cluster analyses supported the notion that trophic trait composition was influenced by proximity to the shelf edge, where food supply is influenced by episodic events that may not be reflected by in situ sedimentary proxies. Our findings add to growing evidence that evaluating trophic traits composition may provide more information regarding functional responses to changes in benthic food supply than either isotopic or taxonomic diversity indices alone.

Food web assessments in the Baltic Sea: Models bridging the gap between indicators and policy needs

Ecosystem-based management requires understanding of food webs. Consequently, assessment of food web status is mandatory according to the European Union’s Marine Strategy Framework Directive (MSFD) for EU Member States. However, how to best monitor and assess food webs in practise has proven a challenging question. Here, we review and assess the current status of food web indicators and food web models, and discuss whether the models can help addressing current shortcomings of indicator-based food web assessments, using the Baltic Sea as an example region. We show that although the MSFD food web assessment was designed to use food web indicators alone, they are currently poorly fit for the purpose, because they lack interconnectivity of trophic guilds. We then argue that the multiple food web models published for this region have a high potential to provide additional coherence to the definition of good environmental status, the evaluation of uncertainties, and estimates for unsampled indicator values, but we also identify current limitations that stand in the way of more formal implementation of this approach. We close with a discussion of which current models have the best capacity for this purpose in the Baltic Sea, and of the way forward towards the combination of measurable indicators and modelling approaches in food web assessments.

A feeding guild indicator to assess environmental change impacts on marine ecosystem structure and functioning

Abstract Integrating food web indicators into ecological status assessments is central to developing effective management measures that can improve degraded ecosystems. This is because they can reveal how ecosystems respond to environmental change that cannot be inferred from studying habitat, species or assemblages alone. However, the substantial investment required to monitor food webs (e.g. via stomach contents analysis) and the lack of internationally agreed approaches to assessing them has hampered their development. Inventories of trophic interactions have been collated world‐wide and across biomes, and can be applied to infer food web structure and energy flow. Here, we compile a new marine dataset containing 8,092 unique predator–prey interactions from 415,294 fish stomachs. We demonstrate how feeding guilds (i.e. groupings based on diet and life stage) could be defined systematically and in a way that is conducive to their application internationally across ecosystems; and apply them to the North Sea fish assemblage to demonstrate their responsiveness to anthropogenic pressures. We found evidence for seven distinct feeding guilds. Differences between guilds were related to predator size, which positively correlated with piscivory, phylogeny, with multiple size classes of a species often in the same guild, and habitat, as pelagic, benthic and shallow‐coastal foraging was apparent. Guild biomasses were largely consistent through time at the North Sea‐level and spatially aggregated at the regional level with change relating to changes in resource availability, temperature, fishing and the biomass of other guilds. This suggests that fish biomass was partitioned across broad feeding and environmental niches, and changes over time were governed partly by guild carrying capacities, but also by a combination of covariates with contrasting patterns of change. Management of the North Sea ecosystem could therefore be adaptive and focused towards specific guilds and pressures in a given area. Synthesis and applications. We propose a food web indicator which has been explicitly called for to inform policy via food web status assessment as part of the European Union's Marine Strategy Framework Directive and the indicator toolkit supporting The Convention for the Protection of the Marine Environment of the North‐East Atlantic (the ‘OSPAR Convention’).

Combining scientific and fishers’ knowledge to co-create indicators of food web structure and function

Abstract In this study, we describe the approach taken by the International Council for the Exploration of the Seas Irish Sea benchmark working group (WKIrish), to co-create diet information for six commercial species using fishers' and scientists knowledge and incorporate it into an existing Ecopath food web model of the Irish Sea. To understand how the co-created diet information changed the model we compared a suite of food web indicators before and after the addition of fishers' knowledge (FK). Of the 80 predator–prey interactions suggested by fishers during workshops, 50 were already included in the model. Although the small number of changes made to the model structure had an insignificant impact on the ecosystem-level indicators, indicators of species hierarchical importance and mixed trophic impacts were significantly changed, particularly for commercial species. FK heightened the importance of discards as a source of food for rays, plaice, and whiting and reduced the importance of cod, toothed whales, and plaice as structural components of the food web. FK therefore led to changes which will influence pairwise advice derived from the model. We conclude by providing lessons from WKIrish which we believe were key to the positive co-production experience and development of integrated management.

Trophic Interactions, Management Trade-Offs and Climate Change: The Need for Adaptive Thresholds to Operationalize Ecosystem Indicators

Ecosystem-based management (EBM) is commonly applied to achieve sustainable use of marine resources. For EBM, regular ecosystem-wide assessments of changes in environmental or ecological status are essential components, as well as assessments of the effects of management measures. Assessments are typically carried out using indicators. A major challenge for the usage of indicators in EBM is trophic interactions as these may influence indicator responses. Trophic interactions can also shape trade-offs between management targets, because they modify and mediate the effects of pressures on ecosystems. Characterization of such interactions is in turn a challenge when testing the usability of indicators. Climate variability and climate change may also impact indicators directly, as well as indirectly through trophic interactions. Together, these effects may alter interpretation of indicators in assessments and evaluation of management measures. We developed indicator networks - statistical models of coupled indicators - to identify links representing trophic interactions between proposed food-web indicators, under multiple anthropogenic pressures and climate variables, using two basins in the Baltic Sea as a case study. We used the networks to simulate future indicator responses under different fishing, eutrophication and climate change scenarios. Responsiveness to fishing and eutrophication differed between indicators and across basins. Almost all indicators were highly dependent on climatic conditions, and differences in indicator trajectories >10% were found only in comparisons of future climates. In some cases, effects of nutrient load and climate scenarios counteracted each other, altering how management measures manifested in the indicators. Incorporating climate change, or other regionally non-manageable drivers, is thus necessary for an accurate interpretation of indicators and thereby of EBM measure effects. Quantification of linkages between indicators across trophic levels is similarly a prerequisite for tracking effects propagating through the food web, and, consequently, for indicator interpretation. Developing meaningful indicators under climate change calls for iterative indicator validations, accounting for natural processes such as trophic interactions and for trade-offs between management objectives, to enable learning as well as setting target levels or thresholds triggering actions in an adaptive manner. Such flexible strategies make a set of indicators operational over the long-term and facilitate success of EBM.

An environmental baseline for food webs at deep-sea hydrothermal vents in Manus Basin (Papua New Guinea)

Food webs and trophic interactions provide a measure of ecosystem function and have been highlighted as an important element for environmental baselines and environmental impact assessments. Stable isotopes have long been used in the deep sea as a means to explore and summarize food webs, especially in chemosynthetic ecosystems, where there may be multiple sources of primary production with distinctive isotopic compositions. Hydrothermal vents in Manus Basin have been targeted for mining and, if mining proceeds, vent food webs will be altered. Here we describe a pre-mining baseline for the food-web state for 3 active vent fields. Manus vents support at least 9 feeding guilds, and both reverse TriCarboxylic Acid (rTCA) and Calvin-Benson-Bassham (CBB) carbon fixation pathways are inferred for symbionts of holobiont taxa. There are site differences in the C-N-S isotopic trait spaces (convex hulls) of Manus Basin vent food webs that likely reflect environmental variability. Isotopic diversity metrics (divergence, dispersion, evenness) are similar in Solwara 1, South Su, and PACMANUS vent food webs, but South Su has a higher degree of isolation in isotopic space (uniqueness). Because convex hull and isotopic diversity metrics are easy to calculate from multidimensional isotopic data, they may be useful food-web indicators for environmental management.

Assessing food web structure in relation to nutrient enrichment, macrophyte collapse and lake resilience in shallow lowland lakes

ABSTRACTWe examined food chain length and food web complexity as indicators for assessing shallow lake resilience from 18 lowland lakes, which included lakes in near-reference condition through to lakes that had undergone catastrophic regime shifts. We observed a trend of decreasing food chain length and food web complexity in lakes that had undergone regime shifts. Across the full trophic gradient, food web metrics were correlated with factors related to trophic status (e.g. chlorophyll-a) and macrophyte loss (e.g. exotic herbivorous fish), which have been previously associated with regime shifts in lakes. With increasing eutrophication, we identified a shift away from omnivory mostly in the lower trophic levels. Factors that impinge on macrophyte communities, such as nutrient loading and herbivory, reduce the resilience of shallow lake ecosystems, which is reflected in changes to lake food web structure. Thus, food web indicators can inform about the sensitivity of shallow lakes to eutrophication.

Vitamine ENA: A framework for the development of ecosystem-based indicators for decision makers

The Water Framework Directive (article 2, paragraph 21) as well as the Marine Strategy Framework Directive (MSFD, Descriptor 4) stress the need for assessing the quality of the structure and the functioning of ecosystems. The MSFD also underlines the urgent need for development, testing, and validation of ecosystem state indicators. Holistic function-based criteria and indicators as provided by Ecological Network Analysis (ENA) could be used to define and assess the ‘Good Environmental Status’ of marine ecosystems. This approach also feeds Ecosystem Based Management (EBM). ENA generally analyses the fluxes' quality of a single medium such as here the carbon fluxes in a food web and produces a number of useful metrics that indicate, inter alia, the total carbon flow through the system, the quality of the functioning of the system or the trophic efficiency of system. A short list of indices [i.e. Detritivory over Herbivory ratio (D/H), Connectance Index (CI), Transfer Efficiency (TE) over trophic levels, System Omnivory Index (SOI), Finn's Cycling Index (FCI), relative Redundancy (R/DC), Average Mutual Information (AMI) and Interaction Strength (IS)] is proposed for practical use. This paper presents a first framework for OSPAR Regional Sea Convention food web indicators based on ENA. These are presented here focusing on their applicability and what is needed for implementation, illustrating their potential use by case studies.

Global Changes Jeopardize the Trophic Carrying Capacity and Functioning of Estuarine Ecosystems

At the interface between terrestrial and marine biomes, estuaries display high ecological productivity and provide goods and services to humans. Associated with many ecological functions, they are nursery, refuge, and growing areas for many species fish. These ecological functions and services depend on both their ecological production and trophic carrying capacity and the durability of food web functioning. These transitional key habitats undergo both strong anthropogenic pressures and climatic influences that impact the structure and dynamics of estuarine biodiversity. In this context, we explore, here, three decades of the Gironde estuary ecosystem history to detect the food web’s response to global changes-induced effect on biodiversity. At least two Ecological Abrupt Shifts associated with deep modifications in the biodiversity at most trophic levels have been documented for this particular ecosystem. Three food web models were thus calibrated, one for each of the three periods discriminated by the two shifts that occurred at the end of the 1980s and the beginning of the 2000s. Results highlighted that the ecotrophic efficiency estimate for subtidal macrofauna and shrimps reached the maximum possible values during the last period. This could mean that the Gironde estuary fully reached its trophic carrying capacity due to a food limitation especially for benthos demersal fish. We also observed a significant decrease in some food web indicators (such as Average Mutual Information, System Omnivory Index, and Average Path Length) usually associated with ecosystem stress, suggesting a significant impact of global change on the Gironde estuary ecosystem health and questioning the sustainability of the ecological functions associated with this ecosystem.

Biodiversity and soil health: the role of the soil food web in soil fertility and suppressiveness to soil-borne diseases

The soil food web plays a fundamental role in ensuring key ecosystem processes, maintaining soil fertility and improving soil suppressiveness to soil-borne diseases. The composition and structure of the soil food web reflect the health and condition of soils, and the effects of soil management - including the use of pesticides, fertilizers, tillage, crop rotation and cover crops - on soil functioning and services which can be assessed by the use of soil food web indicators. My presentation focuses on how the assessment of the nature, diversity and the structure of nematode communities allow diagnosing the status of the soil food web and hence soil health. As main components of the soil microfauna involved at different trophic levels and functional guilds, soil nematode communities - including free-living nematodes - provide unique ecological data on soil processes. The high abundance and the large functional and taxonomic diversity of soil nematodes permit the calculation of a number of indicators of soil food web diversity, maturity and condition. The diversity and biomass of nematodes at different trophic levels can be related to different ecosystem services. Nematodes participate in various soil nutrient and energy channels. Bacterial- and fungal-feeding nematodes are used as indicators of the soil food web mineralization service, and indices derived from their abundances and biomass are related to plant productivity and crop yield, while plant-feeding nematodes are used as indicators of below-ground pest pressure. Nematodes from higher functional guilds, i.e., predators and omnivores, act as natural enemies of below-ground pests, and have been found to be excellent indicators of soil suppressiveness to introduced herbivore prey. The joint assessment of such three components of the food web, largely facilitated by recent on-line tools, allows an integral diagnosis of soil health, as well as the on-farm assessment of the effects of crop management on soil functioning. Soil fertility and soil suppressiveness can be promoted by an adequate soil management able to enhance the diversity and the abundance of soil food web organisms.

A quantitative framework for selecting and validating food web indicators

Finding suitable state indicators is challenging and cumbersome in stochastic and complex ecological systems. Typically, a great focus is given to criteria such as data availability, scientific basis, or measurability. Features associated with the indicator's performance such as sensitivity or robustness are often neglected due to the lack of quantitative validation tools. In this paper, we present a simple but flexible framework for selecting and validating the performance of food web indicators. In specific, we suggest a 7-step process in which indicator performances at a regional scale are quantified and visualized allowing for the selection of complementary indicator suites. We demonstrate its application by comparing the performance of pelagic food web indicators for three basins of the Baltic Sea and by assessing the food web status based on selected indicator suites. Our analysis sheds light on spatial differences in indicator performances with respect to direct and indirect pressures, the role of non-linearity and non-additivity in pressure responses, as well as relationships between indicators caused by species interactions. Moreover, our results suggest that the present food web states in the Bornholm and Gotland basins of the Baltic Sea deviate distinctly from an earlier reference period. We advocate the use of our quantitative framework as decision-support tool for selecting suites of complementary indicators under given management schemes such as the EU Marine Strategy Framework Directive.

Food-web indicators accounting for species interactions respond to multiple pressures

Food-web indicators for marine management are required to describe the functioning and structure of marine food-webs. In Europe, the Marine Strategy Framework Directive (MSFD), intended to lead to a ‘good environmental status’ of the marine waters, requires indicators of the status of the marine environment that also respond to manageable anthropogenic pressures. Identifying such relationships to pressures is particularly challenging for food-web indicators, as they need to be disentangled from linkages between indicators of different functional groups caused by species interactions. Still, such linkages have not been handled in the indicator development. Here we used multivariate autoregressive time series models to identify how fish indicators in an exploited food-web relate to fishing, climate and eutrophication, while accounting for the linkages between indicators caused by species interactions. We assembled 31-year long time series of indicators of key functional groups of fish in the Central Baltic Sea pelagic food-web, which is characterized by strong trophic links between cod (Gadus morhua) and its main fish prey sprat (Sprattus sprattus) and herring (Clupea harengus). These food-web indicators were either abundance-based indicators of key piscivores (cod) and zooplanktivores (sprat and herring) or size-based indicators of the corresponding trophic groups (biomass of large predatory fish (cod≥38cm) and biomass of small prey fish (sprat and herring <10cm)). Comparative analyses of models with and without linkages among indicators showed that for both types of indicators, linkages corresponding to predator-prey feedbacks and intra-specific density-dependence were essential to explain temporal variation in the indicators. Thus, no indicator-pressure relationships could be found that explained the indicators’ variation unless such linkages were accounted for. When accounting for these, we found that the indicators overall respond to multiple pressures acting simultaneously rather than to single pressures, as no pressure alone could explain how the indicators developed over time. The manageable pressures fishing and eutrophication, as well as the prevailing hydrological conditions influenced by climate, were all needed to reproduce the inter-annual changes in these food-web indicators combined, although individual relationships differed between the indicators. We conclude that our innovative indicator-testing framework can therefore be used to identify responses of food-web indicators to manageable pressures while accounting for the biotic interactions in food-webs linking such indicators.

Towards ecosystem-based management: identifying operational food-web indicators for marine ecosystems

Abstract Modern approaches to Ecosystem-Based Management and sustainable use of marine resources must account for the myriad of pressures (interspecies, human and environmental) affecting marine ecosystems. The network of feeding interactions between co-existing species and populations (food webs) are an important aspect of all marine ecosystems and biodiversity. Here we describe and discuss a process to evaluate the selection of operational food-web indicators for use in evaluating marine ecosystem status. This process brought together experts in food-web ecology, marine ecology, and resource management, to identify available indicators that can be used to inform marine management. Standard evaluation criteria (availability and quality of data, conceptual basis, communicability, relevancy to management) were implemented to identify practical food-web indicators ready for operational use and indicators that hold promise for future use in policy and management. The major attributes of the final suite of operational food-web indicators were structure and functioning. Indicators that represent resilience of the marine ecosystem were less developed. Over 60 potential food-web indicators were evaluated and the final selection of operational food-web indicators includes: the primary production required to sustain a fishery, the productivity of seabirds (or charismatic megafauna), zooplankton indicators, primary productivity, integrated trophic indicators, and the biomass of trophic guilds. More efforts should be made to develop thresholds-based reference points for achieving Good Environmental Status. There is also a need for international collaborations to develop indicators that will facilitate management in marine ecosystems used by multiple countries.

Environmental drivers explain regional variation of changes in fish and invertebrate functional groups across the Mediterranean Sea from 1994 to 2012

Functional groups are sets of species that play a similar role in a food web. We defined functional groups of fish species based on their morphological characteristics, while using expert knowledge for invertebrates. We measured 9 morphological traits of 72 fish species, and carried out multivariate analyses to assign fish species to functional groups. The analysis identified 9 trait-based fish functional groups to which were added 3 expert-based invertebrate functional groups. The habitat (position in the water column) and potential diet of each group were identified from the literature. Using the MEDITS bottom trawl survey data collected at 10 to 800 m depth, we calculated relative change in the 12 fish and invertebrate functional group biomasses for 12 Mediterranean areas over the period 1994 to 2012. Multiple regression trees identified 4 regions with similar changes: (1) the Adriatic and the Ionian Sea; (2) the Tyrrhenian Sea and the Strait of Sicily; (3) the Balearic Islands and other enclosed areas such as the Gulf of Lions and Aegean Sea; and (4) the Ligurian Sea and Sardinia. The biomass of all functional groups increased or remained stable in the first 2 regions, while around half the functional group biomasses decreased in the other 2 regions. These regional differences in functional group biomass changes were mainly associated with regional variations in the time trends of bottom water temperature (37%), bottom water dissolved oxygen (23%) and mean catch levels (9%). This study contributes to the EU Marine Strategy Framework Directive by proposing food web indicators based on morphologically and habitat defined functional groups.

Biodiversity and food web indicators of community recovery in intertidal shellfish reefs

In conservation strategies of marine ecosystems, priority is given to habitat-structuring foundation species (e.g. seagrasses, mangroves and reef-building corals, shellfish) with the implicit goal to protect or restore associated communities and their interactions. However, the number and accuracy of community level metrics to measure the success of these strategies are limited. Using intertidal shellfish reefs as a model, we tested to what extent foundation species alter community and food web structure, and explored whether basic metrics of food web structure are useful indicators of ecosystem complexity compared to other often-used indices. We found that shellfish reefs strongly modified community and food web structure by modifying habitat conditions (e.g. hydrodynamics, sediment grain size). Stable isotope-based food web reconstruction captured important differences between communities from bare mudflat and shellfish reefs that did not emerge from classic abundance or diversity measures. On shellfish reefs, link density and the number of top predators were consistently higher, while both connectance and the richness of intermediate species was lower. Species richness (+42%), species density (+79%) and total biomass of benthos, fish and birds (+41%) was also higher on shellfish reefs, but this did not affect the Shannon diversity or Evenness. Hence, our results showed that basic food web metrics such as link density and number of top consumers and intermediate species combined with traditional measures of species richness can provide a robust tool to measure conservation and restoration success. We therefore suggest that these metrics are included as Essential Biodiversity Variables (EBV), and implemented as ecosystem health indicators in legislative frameworks such as the Marine Strategy Framework Directive (MSFD).

Biodiversity in Marine Ecosystems—European Developments toward Robust Assessments

Sustainability of marine ecosystems and their services are dependent on marine biodiversity, which is threatened worldwide. Biodiversity protection is a major target of the EU Marine Strategy Framework Directive, requiring assessment of the status of biodiversity on the level of species, habitats, and ecosystems including genetic diversity and the role of biodiversity in food web functioning and structure. This paper provides a summary of the development of new indicators and refinement of existing ones in order to address some of the observed gaps in indicator availability for marine biodiversity assessments considering genetic, species, habitat, and ecosystem levels. Promising new indicators are available addressing genetic diversity of microbial and benthic communities. Novel indicators to assess biodiversity and food webs associated with habitats formed by keystone species (such as macroalgae) as well as to map benthic habitats (such as biogenic reefs) using high resolution habitat characterization were developed. We also discuss the advances made on indicators for detecting impacts of non-native invasive species and assessing the structure and functioning of marine food-webs. The latter are based on indicators showing the effects of fishing on trophic level and size distribution of fish and elasmobranch communities well as phytoplankton and zooplankton community structure as food web indicators. New and refined indicators are ranked based on quality criteria). Their applicability for various EU and global biodiversity assessments and the need for further development of new indicators and refinement of the existing ones is discussed.