The future of fish-based ecological assessment of European rivers: from traditional EU Water Framework Directive compliant methods to eDNA metabarcoding-based approaches

Most of the present EU Water Framework Directive (WFD) compliant fish-based assessment methods of European rivers are multi-metric indices computed from traditional electrofishing (TEF) samples, but this method has known shortcomings, especially in large rivers. The probability of detecting rare species remains limited, which can alter the sensitivity of the indices. In recent years, environmental (e)DNA metabarcoding techniques have progressed sufficiently to allow applications in various ecological domains as well as eDNA-based ecological assessment methods. A review of the 25 current WFD-compliant methods for river fish shows that 81% of the metrics used in these methods are expressed in richness or relative abundance and thus compatible with eDNA samples. However, more than half of the member states' methods include at least one metric related to age or size structure and would have to adapt their current fish index if reliant solely on eDNA-derived information. Most trait-based metrics expressed in richness are higher when computed from eDNA than when computed from TEF samples. Comparable values are obtained only when the TEF sampling effort increases. Depending on the species trait considered, most trait-based metrics expressed in relative abundance are significantly higher for eDNA than for TEF samples or vice versa due to over-estimation of sub-surface species or under-estimation of benthic and rare species by TEF sampling, respectively. An existing predictive fish index, adapted to make it compatible with eDNA data, delivers an ecological assessment comparable with the current approved method for 22 of the 25 sites tested. Its associated uncertainty is lower than that of current fish indices. Recommendations for the development of future fish eDNA-based indices and the associated eDNA water sampling strategy are discussed.     

The suitability of the marine biotic index (AMBI) to new impact sources along European coasts

In recent years, several benthic biotic indices have been proposed to be used as ecological indicators in estuarine and coastal waters. One such indicator, the AZTI Marine Biotic Index (AMBI), was designed to establish the ecological quality of European coasts. The index examined the response of soft-bottom benthic communities to natural and man-induced disturbances in coastal and estuarine environments. It has been successfully applied to different geographical areas and under different impact sources, with increasing user numbers in European marine waters (Baltic, North Sea, Atlantic and Mediterranean). The AMBI has been used also for the determination of the ecological quality status (EcoQ) within the context of the European Water Framework Directive (WFD).In this contribution, 38 different applications including six new case studies (hypoxia processes, sand extraction, oil platform impacts, engineering works, dredging and fish aquaculture) are presented. The results show the response of the benthic communities to different disturbance sources in a simple way. Those communities act as ecological indicators of the ‘health’ of the system, indicating clearly the gradient associated with the disturbance.     

Relocation of dredged material in estuaries under the aspect of the Water Framework Directive—A comparison of benthic quality indicators at dumping areas in the Elbe estuary

In the context of the requirements of the European Water Framework Directive (WFD) numerous benthic indices have been proposed recently to assess the ecological quality of marine and transitional waters. In several studies these metrics were applied to coastal and estuarine environments under diverse anthropogenic pressures. Although currently the dumping of dredged material is one of the most prominent human impacts that modify estuaries, the performance of benthic indices to detect effects of dredged sediment relocation has not yet been tested explicitly. Hence we examined a selection of common metrics (species richness, Shannon diversity, AMBI, M-AMBI, W-value, BO2A) at 11 dumping and 11 nearby reference areas in the highly modified Elbe estuary (Germany), where permanent dredging is necessary to maintain the depth of the navigation channel. In order to cover the entire estuary, the study area spanned over the whole salinity gradient from limnic to euhaline. Additionally, we investigated changes in benthic communities due to dredged material placement. All indices, except the W-value, were suitable to differentiate between dumping and reference areas and showed significantly better index values exclusively at reference areas. The applicability of AMBI and M-AMBI was restricted in the limnic stretch due to the more frequent occurrence of freshwater species there. The W-value and BO2A were non-satisfactory in the case of azoic sediment, and in most cases these two indices indicated much better ecological status classifications than the other indices tested. Furthermore, the BO2A had restricted applicability with increasing salinity. At eight of eleven sites the benthic communities differed significantly between dumping and reference areas. Our findings show that the power of conventional benthic indices to detect physical disturbances like the dumping of dredged sediment varies greatly. Having this in mind, we suggest to choose carefully the benthic indices for ecological quality assessments according to the WFD in estuaries in order to avoid misclassifications. Such errors may lead to unnecessarily expensive remediation activities or, in the opposite case, to inactivity although actions were necessary. Furthermore, in order to better meet the WFD requirements we suggest that, regarding frequency and volume, dumping should be adapted as far as possible to the natural processes of sediment movement.     

Comparison of two methods for quality assessment of macroalgae assemblages,under different pollution types

The selection of adequate methodologies for the assessment of different biological quality elements is urgently needed for the application of the water framework directive (WFD 2000/60/EEC). In the case of macroalgae in coastal waters of the North East Atlantic, two methodologies have been proposed: the reduced species list (RSL) index and the quality of rocky bottoms (CFR) index. Both methods use multimetric approaches to evaluate the quality of macroalgae assemblages, which are based on community characteristics (species/populations richness, cover, percentage of opportunistic species, ecological state groups ratio, etc.). In this paper the results of applying both indices on three different types of pollution gradients in the North coast of Spain (bay of Biscay) are presented, in order to test their usefulness and intercalibration possibilities. In general terms, the CFR index responded more accurately than the RSL index to the pollution gradients under study. With respect to the indicators used in the current evaluation, richness, opportunistic species and cover seemed to be the most accurate for quality assessment of macroalgal communities. While the first two indicators are taken into account in both indices, the latter (cover) is only considered in the CFR index, even though the abundance of macroalgae is one of the aspects to be included in the evaluation of this biological element, according to the WFD.     

Ecological quality scales based on phytoplankton for the implementation of Water Framework Directive in the Eastern Mediterranean

Structural changes of phytoplankton communities, often expressed through ecological indices, constitute one of the metrics for the implementation of the European Water Framework Directive (WFD). In the current study a thorough analysis of the efficiency of 22 ecological indices was performed and a small number was selected for the development of five-level water quality scales (High, Good, Moderate, Poor, and Bad). The analysis was performed on simulated communities free of the noise of field communities due to uncontrolled factors or stochastic processes. Two criteria were set for the sensitivity of indices, namely their monotonicity and linearity across the studied eutrophication spectrum. The whole procedure was based on the development of a five-level quality assessment scheme based on phytoplankton abundance. Among the indices tested, the Menhinick diversity index and three indices of evenness were the most efficient, showing consistency (monotonic behavior) and linearity and were therefore used for the development of quality scales for the WFD. An Integrated Phytoplankton Index (IPI) based on three phytoplankton metrics, chlorophyll a, abundance, and diversity is also proposed. The efficiency of these indices was evaluated for a number of sites in the Aegean, already classified in the past by various methods based on nutrient concentrations or phytoplankton data. The results indicate that the various phytoplankton metrics (chlorophyll a, abundance, and diversity) assessed or proposed in the current study, carry their own information showing differences in the final classification of areas. Therefore the establishment of synthetic indices as the IPI seems to be advantageous for the integrated assessment of coastal water quality in the framework of European policies as the WFD.     

Detecting benthic community differences: Influence of statistical index and season

An accurate assessment of estuarine condition is critical to determining whether there has been a change from baseline or ‘natural’ conditions; benthic communities are routinely used as an ecological endpoint to make this assessment. We addressed two issues, which arise when attempting to detect differences between benthic communities. The first is the varying sensitivity of metrics, e.g. one metric may not be able to detect differences between two communities where another metric can. The second is the influence of season on the detection of differences between benthic communities from different estuarine systems. In this study, benthic communities taken from depositional sites were sampled in three seasons, at three sites within two relatively pristine estuaries located in southern Massachusetts, USA. Statistical comparisons of benthic community data from the two estuaries were made using three common metrics: species richness, Shannon diversity and Bray–Curtis similarity indices. Significant community differences were found depending upon the index. The Bray–Curtis index, using permutation testing, was the only metric that detected differences between estuaries despite disparate seasonal sampling. This suggests that researchers do not need to be overly constrained to sampling in the same season when testing for differences in benthic communities between estuaries. Additionally, we propose an analytical method to identify anthropogenically impacted estuarine systems.     

Zooplankton as indicators in lakes: a scientific-based plea for including zooplankton in the ecological quality assessment of lakes according to the European Water Framework Directive (WFD)

With the implementation of the EU Water Framework Directive (WFD), the member states have to classify the ecological status of surface waters following standardised procedures. It was a matter of some surprise to lake ecologists that zooplankton were not included as a biological quality element (BQE) despite their being considered to be an important and integrated component of the pelagic food web. To the best of our knowledge, the decision of omitting zooplankton is not wise, and it has resulted in the withdrawal of zooplankton from many so-far-solid monitoring programmes. Using examples from particularly Danish, Estonian, and the UK lakes, we show that zooplankton (sampled from the water and the sediment) have a strong indicator value, which cannot be covered by sampling fish and phytoplankton without a very comprehensive and costly effort. When selecting the right metrics, zooplankton are cost-efficient indicators of the trophic state and ecological quality of lakes. Moreover, they are important indicators of the success/failure of measures taken to bring the lakes to at least good ecological status. Therefore, we strongly recommend the EU to include zooplankton as a central BQE in the WFD assessments, and undertake similar regional calibration exercises to obtain relevant and robust metrics also for zooplankton as is being done at present in the cases of fish, phytoplankton, macrophytes and benthic invertebrates.     

Ability of invertebrate indices to assess ecological condition on intertidal rocky shores

The implementation of directives such as the European Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) has promoted the development of several tools and methods for assessing the ecological health of marine ecosystems. Within the scope of the WFD and in terms of rocky shores, several multimetric tools were developed based on the macroalgae biological quality element (BQE), in addition to those based on macroinvertebrates.The WFD requires member states to assess each BQE separately. The present work aimed to test the ability of ecological indices to distinguish sites within anthropogenic disturbance gradients caused by organic enrichment, using macroinvertebrate communities on intertidal rocky shores. Owing to the lack of more specific indices (for rocky shore), indices based on abundance, diversity and/or taxonomic composition were selected from several widely used indices in ecological studies and/or developed for soft-bottom macroinvertebrate communities.Present findings reveal several indices based on diversity and/or taxonomic composition able to distinguish sites within the disturbance gradients, showing increasing quality from the site nearest the source of organic enrichment to that farthest from it, especially indices calculated using biomass data, and in the summer season. Such results open good perspectives for the use of intertidal macroinvertebrate communities from rocky shores, and also help add the perspective of this biological quality element in the ecological quality assessment of coastal waters.     

Marine angiosperm indices used to assess ecological status within the Water Framework Directive and South African National Water Act: Learning from differences and common issues

This paper reviews and discusses the methods and metrics used for the assessment of the ecological status of marine angiosperms comparing the European with the South African situation. In Europe salt marsh and seagrasses are an important biological element for establishing the ecological quality status of transitional waters and in South Africa changes over time in the salt marsh and submerged macrophyte habitats (species richness, abundance and community composition) is used nationally to assess the health of estuaries. In Europe several studies have developed metrics that include salt marsh species composition and community structure to assess the ecological quality status. Deviation of taxonomic composition and abundance from a reference situation is investigated. Multi-metric approaches have been shown to provide a more holistic view of the ecological status of the ecosystem. Many indices are highly dependent on historical data to assess the deviation from reference conditions. Within the WFD spirit one widely used approach for salt marsh assessment, the Best’s method, the baseline can be determined based on the first sampling effort, by the largest previously recorded size of the salt marsh or using the “maximum potential size” of the salt marsh from habitat prediction models. In South Africa all habitat below the 5 m contour line is considered estuary habitat and any land occupied here by agricultural or other developments is considered as a loss of habitat from the reference condition. For seagrasses European metrics are based on attributes from the community (e.g., taxonomic composition, epiphytes), the population (e.g., bed extent, shoots density), but also quantified at individual species (e.g., leaves length) or physiological levels (e.g., stable isotopic signatures). Seagrass habitats in South African estuaries are highly dynamic in response to floods and an understanding of this is needed before present ecological status can be assessed.     

Assessing fish metrics and biotic indices in a Mediterranean stream: effects of uncertain native status of fish

Implementation of the Water Framework Directive requires tools for measuring and monitoring the ecological status of aquatic ecosystems. Several indices are in use in the Iberian Peninsula, although there has been little comparison among them. We sampled the fish assemblage and limnological features of the Tordera stream (NE Spain) quarterly from September 2001 to May 2003 to evaluate the usefulness of several fish metrics and to compare habitat quality and biotic indices currently in use. Data for eight biotic and abiotic indices for this and three other Catalan river basins were also compiled in order to analyse the relationships among indices. In the Tordera stream, fish abundance and richness increased with stream order except in the last sampling site that had the lowest fish abundance owing to the effects of drought and water abstraction. Although most indices were positively correlated, some displayed low or null correlations particularly for the Tordera basin which is more affected by water abstraction and less by pollution; a commonly used physico-chemical index (ISQA) was the least correlated. In a regional fish index (IBICAT) under development, the brown trout (Salmo trutta) has been previously considered as introduced in the Tordera basin. Here, we report an old published record that demonstrates that trout was present before 1845 and we argue that its status should be considered as uncertain given the current information available. Whether brown trout is treated as native or introduced to this river basin has profound effects on the results of fish metrics because of its dominance in the upper reaches. We briefly discuss the role of introduced species, particularly in headwater streams, in the development of fish indices. Our study exemplifies the need for careful, basin-specific assessment of native/introduced status in the development of fish metrics. Handling editor: K. Martens     

Transitional and coastal waters ecological status assessment: advances and challenges resulting from implementing the European Water Framework Directive

The derivation, performance, sensitivity and inherent uncertainty of ecological quality indicators have become major topics in developing tools for the management of marine, transitional and coastal waters. In reviewing the advances in these waters, related to an ecological status assessment, we show the future challenges to be addressed within the European Water Framework Directive (WFD). Using new analyses carried out under the research project ‘Water Bodies in Europe: Integrative Systems to Assess Ecological status and Recovery’, we provide a complete set of assessments for the biological quality elements (BQEs) (phytoplankton, macroalgae-seagrasses, macroinvertebrates and fish) to be assessed, as well as the validation of existing indicators and multimetric indices and, in some cases, the development of new assessment indices. We show that these indices respond differently to different human pressures and they each have challenges in defining reference conditions against which future changes are judged. In investigating good ecological potential, as the response to heavily modified water bodies, we show that there are flaws in the Directive, not least in its definitions. Our analyses have also focussed on uncertainty in using the indices and we emphasise the problems of defining ecological class boundaries based on indices which themselves may be combined indices (multimetrics). The analysis shows that some of those multimetrics are redundant and/or are inter-correlated and thus may reduce the sensitivity in defining ecological class boundaries. If this is related to the drivers-pressures-state change-impacts-response approach then there are lessons for management measures aimed at achieving good ecological status and even the potential for legal challenges to decisions based on uncertain indices under the WFD. Hence, we conclude the continued need for advances in assessing pressures and gradients, and defining reference conditions for state change, index development, impact assessment and the validation of indices for each BQE.     

A fish-based index for the assessment of the ecological quality of temperate lakes

A fish – based index for the assessment of the ecological quality of natural temperate lakes was developed, in accordance to the requirements of the Water Framework Directive (WFD) 2000/60/EC. As a case study, 11 natural lakes located at northern and western Greece were selected. Fish surveys were conducted during mid summer to mid autumn in 2010, 2011 and 2012 using Nordic gillnets and electrofishing. Environmental parameters and anthropogenic pressures were assessed for each lake. Fish species richness, abundance, trophic, reproductive and habitat functional guilds were used for extracting a set of 107 metrics, meeting the requirements of the WFD. All metrics were initially tested as candidates for the index development. A stepwise linear regression of each metric against environmental parameters (lake area, altitude, maximum depth, alkalinity) and anthropogenic pressures (drainage area covered by non-natural land uses – NNLC, water total phosphorus concentrations – TP, Lake Habitat Modification Score – LHMS) was initially conducted for ensuring pressure-response relationships. Reference conditions for each lake were estimated by the hindcasting procedure and the ecological quality for each lake was expressed as the ecological quality ratio (EQR) by a value ranging from 0 (poor quality) to 1 (excellent quality). Two fish fauna metrics, the relative numerical abundance of introduced species (Introduced_a) and the relative biomass of omnivorous species (OMNI_b) were finally extracted as the most significant, responding to LHMS and TP, respectively. The final index was expressed as the mean values of the EQRs of these two metrics. The multimetric fish index presented herein could serve as a tool for assessing the ecological quality of natural lakes at broad geographical scale and generally, in the Mediterranean temperate lakes with similar hydromorphological characteristics.     

Macrophyte communities in unimpacted European streams: variability in assemblage patterns, abundance and diversity

Macrophytes are an important component of aquatic ecosystems and are used widely within the Water Framework Directive (WFD) to establish ecological quality. In the present paper we investigated macrophyte community structure, i.e., composition, richness and diversity measures in 60 unimpacted stream and river sites throughout Europe. The objectives were to describe assemblage patterns in different types of streams and to assess the variability in various structural and ecological metrics within these types to provide a basis for an evaluation of their suitability in ecological quality assessment. Macrophyte assemblage patterns varied considerably among the main stream types. Moving from small-sized, shallow mountain streams to medium-sized, lowland streams there was a clear transition in species richness, diversity and community structure. There was especially a shift from a predominance of species-poor mosses and communities dominated by liverwort in the small-sized, shallow mountain streams to more species-rich communities dominated by vascular plants in the medium-sized, lowland streams. The macrophyte communities responded to most of the features underlying the typological framework defined in WFD. The present interpretation of the WFD typology may not, however, be adequate for an evaluation of stream quality based on macrophytes. First and most important, by using this typology we may overlook an important community type, which is characteristic of small-sized, relatively steep-gradient streams that are an intermediate type between the small-sized, shallow mountain streams and the medium-sized, lowland streams. Second, the variability in most of the calculated metrics was slightly higher when using the pre-defined typology. The consistency of these results should be investigated by analysing a larger number of sites. Particularly the need of re-defining the typology to improve the ability to detect impacts on streams and rivers from macrophyte assemblage patterns should be investigated. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Biogeography of benthic macroinvertebrates in estuaries along the Gulf of Mexico and western Atlantic coasts1,2

A multimetric fish Index of Biotic Integrity (IBI) was composed to assess the biotic integrity of Flandrian water bodies. As fish communities differ substantially between standing waters, running waters of the bream zone and running waters of the barbel zone, eight candidate metrics for each of these water types or zones were identified, representing three major classes of biological attributes. These are species richness and composition, fish condition and abundance, trophic composition. The metrics were tested and modified where needed. The IBI was applied throughout Flanders on 104 locations in standing waters, 500 locations in waters of the bream zone and 257 locations in waters of the barbel zone. Standing waters scored substantially different from running waters. Standing waters rarely contained no fish at all, but their fish communities were very often poor to very poor. Waters of the bream and barbel zone were often fishless (respectively 40% and 35% of all locations contain no fish), but the locations with fish usually scored reasonable to poor. Only 18.5% of all locations were classified as reasonable to excellent (IBI classes 4 or lower on a scale from 1 to 9) and were considered to satisfy the basic ecological quality demands. The Leie-, Dijle-, Dender- and Schelde-basins had a very poor quality (more than 50% of the locations contained no fish). The Maas-, Grote and Kleine Nete-basins scored rather well, with respectively, 44%, 48% and 68% of the locations achieving an IBI of 4 or lower. The IBI is a valuable and complementary tool to assess the ecological quality of water bodies as suggested in the proposal for a Water Framework Directive by the European Commission.     

Quantifying uncertainties in biologically-based water quality assessment: A pan-European analysis of lake phytoplankton community metrics

Lake phytoplankton are adopted world-wide as a sensitive indicator of water quality. European environmental legislation, the EU Water Framework Directive (WFD), formalises this, requiring the use of phytoplankton to assess the ecological status of lakes and coastal waters. Here we provide a rigorous assessment of a number of proposed phytoplankton metrics for assessing the ecological quality of European lakes, specifically in response to nutrient enrichment, or eutrophication, the most widespread pressure affecting lakes. To be useful indicators, metrics must have a small measurement error relative to the eutrophication signal we want them to represent among lakes of different nutrient status. An understanding of variability in metric scores among different locations around a lake, or due to sampling and analytical variability can also identify how best this measurement error is minimised.To quantify metric variability, we analyse data from a multi-scale field campaign of 32 European lakes, resolving the extent to which seven phytoplankton metrics (including chlorophyll a, the most widely used metric of lake quality) vary among lakes, among sampling locations within a lake and through sample replication and processing. We also relate these metrics to environmental variables, including total phosphorus concentration as an indicator of eutrophication.For all seven metrics, 65–96% of the variance in metric scores was among lakes, much higher than variability occurring due to sampling/sample processing. Using multi-model inference, there was strong support for relationships between among-lake variation in three metrics and differences in total phosphorus concentrations. Three of the metrics were also related to mean lake depth. Variability among locations within a lake was minimal (<4%), with sub-samples and analysts accounting for much of the within-lake metric variance. This indicates that a single sampling location is representative and suggests that sub-sample replication and standardisation of analyst procedures should result in increased precision of ecological assessments based upon these metrics.For three phytoplankton metrics being used in the WFD: chlorophyll a concentration, the Phytoplankton Trophic Index (PTI) and cyanobacterial biovolume, >85% of the variance in metric scores was among-lakes and total phosphorus concentration was well supported as a predictor of this variation. Based upon this study, we can recommend that these three proposed metrics can be considered sufficiently robust for the ecological status assessment of European lakes in WFD monitoring schemes.     

Estimating confidence of European WFD ecological status class and WISER Bioassessment Uncertainty Guidance Software (WISERBUGS)

The Water Framework Directive (WFD) requires estimates of the confidence and precision associated with any scheme for assessing and monitoring the ecological status class of any European rivers, lakes, transitional or coastal waters. This is a complex important issue, especially for waterbody assessments based on multiple metrics and/or two or more taxonomic groups. This paper aims to contribute towards improving understanding and providing practical approaches to assessing confidence of class by (i) discussing the various sources and causes of uncertainty, (ii) using UK rivers macroinvertebrate datasets to illustrate the estimation of replicate, temporal and spatial variance components and the implications for water body metric precision, confidence of class and optimal sampling design, (iii) introducing new freely available general software WISER Bioassessment Uncertainty Guidance Software (WISERBUGS) which uses prior sampling uncertainty estimates with user-specified metrics, class limits and metric combination rules to simulate the joint sampling uncertainty in metric EQR values and provide estimates of confidence of class based on individual metrics, (optionally weighted) multi-metric indices and/or multi-metric classification rules (worst case, mean or median class) based on one or more WFD biological quality elements.     

Biological quality metrics: their variability and appropriate scale for assessing streams

The concept of spatial scale is at the research frontier in ecology, and although focus has been placed on trying to determine the role of spatial scale in structuring communities, there still is a further need to standardize which organism groups are to be used at which scale and under which circumstances in environmental assessment. This paper contributes to the understanding of the variability at different spatial scales (reach, stream, river basin) of metrics characterizing communities of different biological quality elements (macrophytes, fishes, macroinvertebrates and benthic diatoms) as defined by the Water Framework Directive. For this purpose, high-quality reaches from medium-sized lowland streams of Latvia, Ecoregion 15 (Baltic) were sampled using a nested hierarchical sampling design: (river basin → stream → reach). The variability of metrics within the different groups of biological quality elements confirmed that large-bodied organisms (macrophytes and fish) were less variable than small-bodied organisms (macroinvertebrates and benthic diatoms) at reach, stream and river basin scales. Single metrics of biological quality elements had the largest variation at the reach scale compared with stream and basin scales. There were no significant correlations between biodiversity indices of the different organism groups. The correlation between diversity indices (Shannon’s and Simpson’s) of the biological quality elements (macrophytes, fish, benthic macroinvertebrates and benthic diatoms) and a number of measured environmental variables varied among the different organism groups. Relationships between diversity indices and environmental factors were established for all groups of biological quality elements. Our results showed that metrics of macrophytes and fish could be used for assessing ecological quality at the river basin scale, whereas metrics of macroinvertebrates and benthic diatoms were most appropriate at a smaller scale.     

Lake connectivity and fish species richness in southern Brazilian coastal lakes

Connectivity is a key factor in metacommunity ecology, because it influences dispersal and colonization rates. However, it has received less attention in aquatic than in terrestrial ecology research. We investigated whether connectivity is a good predictor of species richness in functional fish communities (freshwater, FS; estuarine, ES and estuarine-freshwater, EFS) from 31 coastal lakes in southern Brazil. We used a model selection approach, including lake area and distance from the ocean as additional predictors of species richness and two connectivity metrics: primary connectivity (C _P) and estuarine connectivity (C _E), which measure connectivity to neighboring lakes and system-wide connectivity, respectively. Both metrics estimate functional connectivity and were calculated on habitat-based cost distances. Connectivity was more important for predicting richness of functional communities than for total richness, particularly C _E, which was distinctively related to each functional fish community richness (directly related to ES and EFS, and inversely related to FS; C _P was related only to ES). Remarkably, connectivity was more important than area for predicting ES and EFS richness. These results add support to dispersal limitation as an important mechanism influencing fish communities. We suggest that incorporating environmental filters (habitat type) to quantify connectivity is useful for accessing the patterns of species richness.     

Addressing a gap in the Water Framework Directive implementation: Rocky shores assessment based on benthic macroinvertebrates

A gap in the European Water Framework Directive (WFD) is addressed, aiming for the development of an ecological quality status assessment tool based solely on the Biological Quality Element benthic macroinvertebrates from intertidal rocky shores. The proposed Rocky shore Macroinvertebrates Assessment Tool (RMAT) was tested and validated along disturbance gradients (organic enrichment). During the whole process, the response of widely used metrics (e.g. Hurlbert index, Shannon-Wiener index, AZTI’s Marine Biotic Index; Bentix biotic index) and models (i.e., metrics combined) was compared to results provided by the Marine Macroalgae Assessment Tool to the same sampling sites.The RMAT is a multimetric index compliant with the WFD based on the benthic macroinvertebrates community, combining ‘abundance’ (Hurlbert index) and ‘taxonomic composition’ (Bentix index using density and biomass data) metrics. It performed well along anthropogenic disturbance gradients, showing ecological quality increasing from close to far away from the disturbance.The RMAT is a promising tool for rocky shore ecological assessment in the scope of the WFD or other monitoring activities worldwide.