Classification efficiency of the B-IBI comparing water body size classes in Chesapeake Bay

The Benthic Index of Biotic Integrity (B-IBI) was developed and is currently employed for environmental assessment in Chesapeake Bay. The index consists of a variety of benthic community metrics (e.g. abundance, biomass, diversity, stress tolerance groups, etc.) scored by thresholds applied to seven benthic community habitats (tidal freshwater, oligohaline, low mesohaline, high mesohaline mud, high mesohaline sand, polyhaline mud, and polyhaline sand) This index was verified as being a sensitive and robust tool for summarizing the status of benthic communities. In our study we tested the classification efficiency of the index using new benthic data by characterizing each sample a priori as degraded or undegraded using criteria of sediment contaminant levels, bioassays and bottom dissolved oxygen levels. A primary objective of our study was to test the classification efficiency of the B-IBI in small water bodies connected to larger water bodies of the mainstems of the large rivers of Chesapeake Bay, as well as the efficiency of the index over time (1990 through 2009). The B-IBI was affected by the size of the water body, e.g., index accuracy was higher for water bodies in small watersheds in lower salinity habitats, whereas large water bodies of the mainstem of rivers were better classified by the B-IBI in habitats with higher salinities. Across the seven benthic habitat types overall correct classification was moderate to low and lower for correctly classifying undegraded sites. In general the index metrics showed some deficiencies that suggest improvements could be made by recalibrating existing metric thresholds or selecting new suitable metrics.     

Depth-related patterns in benthic community condition along an estuarine gradient in Chesapeake Bay,USA

We tested whether macrobenthic community condition varies significantly with water depth in a variety of regions of Chesapeake Bay, USA. Benthic community condition was characterized using the Benthic Index of Biotic Integrity (B-IBI) previously developed for the Bay. We applied two water depth thresholds intended to emphasize the ecological importance and/or anthropogenic impacts upon shallow-water regions. The first threshold of 2 m emphasizes restoring and supporting submerged aquatic vegetation while the second threshold of 4 m emphasizes the zone of maximum anthropogenic impact upon natural ecosystem functions. An a priori expectation is that benthic community condition may worsen with increasing depth, specifically in regions (1) where water column stratification at depth results in prolonged low dissolved oxygen levels or (2) where net deposition at depth results in higher levels of hydrophobic, sediment-bound contaminants. Samples collected from a major tributary of Chesapeake Bay, the York River estuary, spanned the entire salinity range from tidal freshwater to polyhaline. We also tested the shallow-water depth thresholds using data from the Virginia Mainstem of Chesapeake Bay and the Southern Branch of the Elizabeth River. These two polyhaline regions are characterized as having the best and worst benthic community condition in Chesapeake Bay. At the scale of the entire tidal York River system, there were no significant differences in benthic community condition with water depth. However, two salinity regions, low mesohaline and polyhaline, had significant depth effects with the shallowest water depth zone significantly different from the other two depth regions. For the low mesohaline region benthic community condition was worse at the shallowest depth and for the polyhaline region the shallowest depth was better comparing the three depth regions. No depth-related differences in the B-IBI were found for the two additional Chesapeake Bay strata, the Virginia Mainstem characterized with the lowest levels of benthic community degradation and for the Southern branch of the Elizabeth River, characterized by the highest levels of benthic community degradation. We conclude that the ecological state of Chesapeake Bay subtidal benthic communities is adequately characterized by randomly sampling all depths without further stratification into shallow and deeper regions.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

Assessing benthic health in stressed subtropical estuaries,eastern Florida,USA using AMBI and M-AMBI

The Indian River Lagoon (IRL) and the St. Lucie Estuary (SLE), both located in Florida, USA, are affected by a variety of anthropogenic pressures. Benthic macroinvertebrates have been monitored quarterly since February 2005, at 15 stations, in order to assess benthic health. Since the SLE and IRL are situated in a subtropical area, it is affected by two major climatic seasons, dry (winter) and wet (summer). This contribution investigates the application of the AZTI's Marine Biotic Index (AMBI) and multivariate-AMBI (M-AMBI), to assess the ecological status of these estuaries. AMBI was firstly calculated after assigning most of the previously unassigned species to each of the five ecological groups (from sensitive to first order opportunistic species). Three main benthic assemblages, associated to oligohaline, meso-polyhaline and euhaline stretches, have been identified within the area. Reference conditions of richness, Shannon's diversity and AMBI have been derived for these assemblages; M-AMBI has then been calculated. Both methods show that the inner part of the SLE is affected by anthropogenic pressures (increased freshwater inflow, with elevated nutrient input, and sedimentation), whilst the IRL is less affected. We have demonstrated that AMBI and M-AMBI are insensitive to the dramatic seasonal changes occurring in the SLE/IRL. At some of the stations a significant positive trend in benthic quality has been identified, linked to the polluted freshwater discharges decrease. The use of both tools seems adequate in assessing benthic health in this subtropical area.     

Estuarine fish communities respond to climate variability over both river and ocean basins

Estuaries are dynamic environments at the land–sea interface that are strongly affected by interannual climate variability. Ocean–atmosphere processes propagate into estuaries from the sea, and atmospheric processes over land propagate into estuaries from watersheds. We examined the effects of these two separate climate‐driven processes on pelagic and demersal fish community structure along the salinity gradient in the San Francisco Estuary, California, USA. A 33‐year data set (1980–2012) on pelagic and demersal fishes spanning the freshwater to marine regions of the estuary suggested the existence of five estuarine salinity fish guilds: limnetic (salinity = 0–1), oligohaline (salinity = 1–12), mesohaline (salinity = 6–19), polyhaline (salinity = 19–28), and euhaline (salinity = 29–32). Climatic effects propagating from the adjacent Pacific Ocean, indexed by the North Pacific Gyre Oscillation (NPGO), affected demersal and pelagic fish community structure in the euhaline and polyhaline guilds. Climatic effects propagating over land, indexed as freshwater outflow from the watershed (OUT), affected demersal and pelagic fish community structure in the oligohaline, mesohaline, polyhaline, and euhaline guilds. The effects of OUT propagated further down the estuary salinity gradient than the effects of NPGO that propagated up the estuary salinity gradient, exemplifying the role of variable freshwater outflow as an important driver of biotic communities in river‐dominated estuaries. These results illustrate how unique sources of climate variability interact to drive biotic communities and, therefore, that climate change is likely to be an important driver in shaping the future trajectory of biotic communities in estuaries and other transitional habitats.     

Pollution and tidal benthic communities of the James River Estuary,Virginia

Distribution of benthic communities in the estuarine portion of the James River was controlled mainly by salinity. Pollution effects were localized and difficult to assess because of a rigorous physical environment. Mesohaline and oligohaline communities were very similar to those in other estuaries of the eastern United States. Macrobenthic densities were most severely depressed in tidal freshwater habitats near Richmond & Hopewell, where the major portion of the pollution load enters the river. Cluster analysis of species distributional patterns and ordination of pollution and physical parameters produced similar results, dividing the river into mesohaline, oligohaline, and upper and lower tidal freshwater zones. Further analysis of only the tidal freshwater portion indicated the distribution of benthic communities reflected the location and concentration of pollution sources along the river. Tidal freshwater communities were dominated by the Asiatic clam, Corbicula fluminea, tubificid oligochaetes of the genus Limnodrilus and the chironomid insect larva Coelotanypus scapularis. The fauna of the freshwater zones was very eurytopic with respect to sediment type and has a great resemblance to the fauna of eutrophic lakes. The classical concept of a sharp increase in number of species occurring from oligohaline to freshwater zones was found to be misleading. This increase does not occur until free flowing (or lotic) freshwater areas of greater habitat diversity are reached.     

The structure of population genetic diversity in <Emphasis Type="Italic">Vallisneria</Emphasis><Emphasis Type="Italic">americana</Emphasis> in the Chesapeake Bay: implications for restoration

Submersed aquatic macrophyte beds provide important ecosystem services, yet their distribution and extent has declined worldwide in aquatic ecosystems. Effective restoration of these habitats will require, among other factors, reintroduction of genetically diverse source material that can withstand short- and long-term environmental fluctuations in environmental conditions. We examined patterns of genetic diversity in Vallisneria americana because it is a cosmopolitan freshwater submersed aquatic macrophyte and is commonly used for restoring freshwater habitats. We sampled 26 naturally occurring populations of V. americana in the Chesapeake Bay estuary and its tributaries and found that the majority of populations have high genotypic diversity and are not highly inbred. Fourteen of the populations had high allelic and genotypic diversity and could serve as source sites for restoration material. However, substantial geographic structuring of genetic diversity suggests that caution should be used in moving propagules to locations distant from their source. In particular, we suggest that propagules at least be limited within four primary geographic areas that correspond to freshwater tidal and non-tidal, oligohaline, and seasonally mesohaline areas of the Chesapeake Bay.     

Stability of Bacterial Composition and Activity in Different Salinity Waters in the Dynamic Patos Lagoon Estuary: Evidence from a Lagrangian-Like Approach

We employed a Lagrangian-like sampling design to evaluate bacterial community composition (BCC—using temporal temperature gel gradient electrophoresis), community-level physiological profiles (CLPP—using the EcoPlate? assay), and influencing factors in different salinity waters in the highly dynamic Patos Lagoon estuary (southern Brazil) and adjacent coastal zone. Samples were collected monthly by following limnetic–oligohaline (0–1), mesohaline (14–16), and polyhaline (28–31) waters for 1 year. The BCC was specific for each salinity range, whereas the CLPPs were similar for mesohaline and polyhaline waters, and both were different from the limnetic–oligohaline samples. The limnetic–oligohaline waters displayed an oxidation capacity for almost all organic substrates tested, whereas the mesohaline and polyhaline waters presented lower numbers of oxidized substrates, suggesting that potential activities of bacteria increased from the polyhaline to oligohaline waters. However, the polyhaline samples showed a higher utilization of some simple carbohydrates, amino acids, and polymers, indicating a shortage of inorganic nutrients (especially nitrogen) and organic substrates in coastal saltwater. The hypothesis of bacterial nitrogen limitation was corroborated by the higher Nuse index (an EcoPlate?-based nitrogen limitation indicator) in the polyhaline waters and the importance of NO₂ ^?, NO₃ ^?, low-molecular-weight substances, and the low-molecular-weight:high-molecular-weight substances ratio, indicated by the canonical correspondence analyses (CCAs). Our results demonstrate the important stability of microbial community composition and potential metabolic activity in the different water salinity ranges, which are independent of the region and time of the year of sample collection in the estuary. This is a quite unexpected result for a dynamic environment such as the Patos Lagoon estuary.     

Macrobenthic Distribution within the Sediment along an Estuarine Salinity Gradient

The distribution of the macrobenthic infaunal community within the upper 25 cm of the sediment was studied at 16 stations in the lower Chesapeake Bay. Stations were located from the tidal freshwater to the polyhaline zone of major tributaries (James, York and Rappahannock Rivers) and in the polyhaline portion of the lower bay mainstem. Profiles for total number of individuals, total ash-free dry weight biomass and species encountered with depth were calculated. Except for the deep dwelling bivalve, Macoma balthica, tributary macrobenthic communities had a shallow depth distribution compared to the mainstem sites which were found in generally coarser sediments in the higher salinity region of the estuary.     

Evaluating the influence of off-shore cage aquaculture on the benthic ecosystem in Alghero Bay (Sardinia,Italy) using AMBI and M-AMBI

The impact of an off-shore fish farm in Alghero Bay (northwest Sardinia, Italy) on the benthic ecosystem was investigated in 2007 and 2008. In addition to studying the chemical and physical characteristics of the area (i.e., currents and sediment analyses), some biological analyses were also performed. The AZTI's Marine Biotic Index (AMBI) and the multivariate AMBI (M-AMBI) were calculated, which are being used in assessing the ecological status of benthic communities within the European Water Framework Directive (WFD). Clear impact gradients were detected according to both methods; they are related to farm production, prevailing currents, and characteristics of the area (i.e., water depth and distance to the cages). The site affected most was detected within 84 m from the cages; the area that no longer showed effects was over 907 m from the cages. The gradient is shown by decreasing AMBI values and percentage of opportunistic species and increasing richness, diversity, and the presence of sensitive species. This study highlights the importance of setting reference conditions for different areas when calculating M-AMBI. These reference conditions correspond to those in undisturbed sites in the opposite direction of the prevailing currents within the area.     

莱州湾小清河口近岸海域底栖生境健康评价

于2019年7月、8月和9月对莱州湾小清河口近岸海域的大型底栖动物进行调查,对该海域大型底栖动物群落的种类组成和群落结构等进行研究,利用丰度/生物量比较曲线法、AMBI指数法和M-AMBI指数法对研究海域大型底栖动物群落健康和底栖生境健康状况进行评价。研究结果表明,2019年7月、8月和9月共采集到大型底栖动物64种,其中多毛类24种,甲壳类19种,软体动物17种,其他类群4种。该海域的优势种为光滑河蓝蛤（Potamocorbula laevis）、彩虹明樱蛤（Moerella iridescens）、半褶织纹螺（Nassarius semiplicatus）、四角蛤蜊（Mactra veneriformis）,寡鳃齿吻沙蚕（Nephthys oligobranchia）、中蚓虫（Mediomastus californiensis）、东方长眼虾（Ogyrides orientalis）、尖齿拳蟹（Philyra acutidens）和短角双眼钩虾（Ampelisca brevicornis）,其中彩虹明樱蛤和寡鳃齿吻沙蚕在三次调查中均为优势物种,优势度明显。群落结构聚类分析和多维尺度分析表明,7月研究海域的大型底栖动物群落以10%的相似性可以分为3组,8月以18%相似性可以分为4组,9月以19%的相似性可以分为3组,三次调查的群落结构相似度均较低。丰度/生物量比较曲线法研究结果显示,底栖动物群落生物量优势显著,群落处于未干扰状态。AMBI指数及M-AMBI指数分析结果表明,莱州湾小清河口近岸海域底栖生境处于未干扰或者轻度干扰的状态,健康状况处于高等或者优良的状态。     

Assessing the suitability of five benthic indices for environmental health assessment in a large subtropical South American estuary

Despite the increased and widespread usage of benthic indices for environmental health assessment, some methodological ambiguities remain to be solved. We tested the congruence and consistency of the benthic indices ITI, BO2A, BENTIX, AMBI and M-AMBI in a subtropical estuary (Paranaguá Bay, Brazil). Indices were applied to non-vegetated tidal flats increasingly contaminated by sewage to test: (i) correlations with molecular biomarkers of sewage (consistency); and (ii) evaluate the overall agreement/similarity of responses (congruence). The responses of the benthic indexes ITI, AMBI and BO2A were congruent among themselves and consistent with molecular biomarkers values. BENTIX and M-AMBI were less consistent and congruent and possibly need a readjustment of boundaries for subtropical habitats. The indices seemed robust to natural background yearly variations not related to contamination. Faecal sterols associated to nutrient contents suitably supported the validation of indices and could integrate reference conditions for sewage impacted coastal habitats. Benthic indices can successfully integrate management guidelines, but their suitable application demands further research on tolerance shifts of key indicator species.     

Setting reference conditions for mesohaline and oligohaline macroinvertebrate communities sensu WFD: Helping to define achievable scenarios in basin management plans

The Water Framework Directive requires all Member States to achieve good ecological quality status for all waters (e.g., transitional waters). For that purpose, Member States must assess water bodies based on information on the Biological Quality Elements listed for each of them (e.g., benthic macroinvertebrates). However, the production of such a quality status classification (high, good, moderate, poor, bad) requires high reference conditions (associated with the absence of, or very low, human pressure) against which the deviation of the samples to be assessed can be measured. In transitional waters, upper stretches have seldom been included in monitoring activities, resulting in very little knowledge of mesohaline and oligohaline areas, which means further difficulty when defining the required reference conditions for these zones.Regarding the benthic macroinvertebrates, large datasets from the mesohaline and oligohaline stretches of the Mondego estuary (four seasons, five years, environmental parameters, density and biomass data) were used to estimate high reference condition values. In terms of environmental conditions, summer was identified as the most stable season and the most suitable for defining reference conditions for selected ecological indicators. For each indicator, the multivariate linear model expressing the best correlation with measured environmental parameters was selected. These models were used afterwards, by replacing the environmental parameters in those equations with their high reference values, to calculate the reference condition for each ecological indicator.Generally, macrobenthic communities within each stretch changed over the years, being mainly influenced by salinity and sediment organic matter. In both stretches, only a few taxa occurred and two species (the amphipod Corophium multisetosum and the bivalve Corbicula fluminea) were clearly dominant. Diversity values (for Margalef, Shannon and ES₅₀ – Hurlbert indices) were low in both stretches, although higher in the mesohaline, and for the most part the ecological condition was low (AMBI – AZTI Marine Biotic Index, MEDDOC – Mediterranean Occidental index, BENTIX biotic index, BO2A – Benthic Opportunistic Annelida Amphipod index). On the whole, the RC estimated for each index followed the same trend, being different for each stretch and below those found for lower sections of the estuary in other surveys.     

Vegetation change from chronic stress events: Detection of the effects of tide gate removal and long‐term drought on a tidal marsh

Question: Chronic stress events are defined as disturbance events that exceed the lifespan of the dominant plant species, fluctuate in intensity and lack abruptness or physical destruction of biomass. Can the effects of chronic stress events be measured on vegetation communities? Did two chronic stress events, the removal of a tide gate and a four year drought, cause a temporary or permanent shift in the vegetation communities of a tidal marsh? Location: Tidal marsh in southeastern United States. Methods: Change in species composition and dominance and community change on a landscape level salinity gradient were measured between time periods ranging from four months to seven years to construct a statistical baseline reference community at freshwater, oligohaline, and mesohaline sections of a tidal marsh. Statistical shifts in the plant community were defined as changes in the plant community that fell outside of the defined baseline reference community. Results: Plant community changes outside of the reference community occurred in 13 out of 378 community comparisons. Removal of the tide gate had a greater effect on interstitial salinity levels than the drought and was most intense in the oligohaline marsh, where between 20 to 45% of the freshwa‐ter/oligohaline community types permanently converted to oligohaline community types. However, community shifts in the freshwater and oligohaline marsh induced by the drought were temporary, lasting from 1 to 3+ years. Neither chronic stress event permanently altered the mesohaline plant communities. Conclusion: The effects of chronic stress events could be detected; an extended historical record of vegetation change (18 years) was necessary to identify community shifts outside of a reference condition of the community and to determine if those shifts were permanent or temporary.     

Plant responses to increased inundation and salt exposure: interactive effects on tidal marsh productivity

Flooding and high salinity generally induce physiological stress in wetland vascular plants which may increase in intensity with sea-level rise (SLR). We tested the effects of these factors on seedling growth in a transplant experiment in a macrotidal estuary in the Pacific Northwest. Seven common wetland species were grown at mean higher high water (MHHW, a typical mid-marsh elevation), and at 25 and 50 cm below MHHW in oligohaline, mesohaline, and polyhaline marshes. Increased flooding reduced shoot and root growth in all species, including those typically found at middle or lower tidal elevations. It also generally disproportionately reduced root biomass. For more sensitive species, biomass declined by >50 % at only 25 cm below MHHW at the oligohaline site. Plant growth was also strongly reduced under polyhaline conditions relative to the less saline sites. By combining inundation and salinity time-series measurements we estimated a salt exposure index for each site by elevation treatment. Higher values of the index were associated with lower root and shoot biomass for all species and a relatively greater loss of below-ground than above-ground production in most species. Our results suggest that inundation and salinity stress individually and (often) interactively reduce productivity across a suite of common marsh species. As relative SLR increases the intensity of stress on coastal marsh plants, negative effects on biomass may occur across a range of species and especially on below-ground production.     

M-AMBI derived from taxonomic levels higher than species allows Ecological Status assessments of benthic habitats in new geographical areas

Under the Water Framework Directive (WFD) benthic Ecological Quality Ratios (EQRs) are important tools for assessing Ecological Status (ES) of coastal and transitional waters. Calculation of the Multivariate-AZTI Marine Biotic Index (M-AMBI) EQR is based on the proportions of sensitive and stress tolerant benthic invertebrate species, number of species and Shannon–Wiener diversity. The sensitivity of many tropical/sub-tropical taxa has not yet been determined, presenting a barrier to the direct transfer of WFD EQRs, and the ideas underpinning them, to the management of coastal waters beyond Europe. To overcome this we examine using higher taxonomic level data with M-AMBI.Before applying such approaches to assessing ES in new geographical regions it is essential to determine the effects of using higher taxonomic level data on M-AMBI in areas where the tool was developed. To this end, we use macrofaunal data from three well studied sites in north-western Europe to examine the effects of using taxonomic level data higher than species on M-AMBI. Using the European datasets M-AMBI ES classification was shown to be robust to changes in taxonomic level data. We test the suitability of family-level M-AMBI for assessing ES in subtropical Hong Kong waters. Family level M-AMBI was useful in detecting stress in Hong Kong, where it successfully detected temporal and spatial shifts in ES in response to seasonal hypoxia and salinity variability, and anthropogenic organic enrichment.     

Development of a multimetric approach to assess perturbation of benthic macrofauna in Zostera noltii beds

Biotic indices based on soft-bottom macrozoobenthic communities are currently used throughout Europe to assess the ecological quality of coastal and transitional water bodies according to the European Water Framework Directive. However, the performance of the currently available biotic indices still has to be tested against a variety of different impact sources. In particular, physical perturbations have received much less attention than other kind of disturbances. This study consisted in testing the capacity of currently available uni- (BOPA, AMBI and BENTIX) and multivariate (M-AMBI) Biotic Indices to assess the ecological impact of the destruction of a Zostera noltii seagrass bed in Arcachon Bay (France) following sediment deposits. Changes of habitat after this physical perturbation were hardly assessed by any of these Biotic Indices whereas analysis of the benthic community showed drastic changes of structure following the perturbation and no recovery after 15 months. This study demonstrates that these Biotic Indices must be integrated into a multimetric approach which describes better the biological integrity of the benthic community by including a complementary set of metrics. A new multimetric approach, named MISS (Macrobenthic Index of Sheltered Systems) is proposed. MISS correctly highlighted the destruction of the seagrass beds, by using 16 metrics describing the biological integrity of the macrofauna.     

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.     

Is there a significant relationship between the benthic status of an area,determined by two broadly-used indices,and best professional judgment?

Two benthic indices to assess the quality status (the AZTI's Marine Biotic Index (AMBI) and multivariate-AMBI (M-AMBI)) are being used extensively in different habitats worldwide. We try to interpret what is behind these indices making them suitable for different habitats. To demonstrate that, we used best professional judgment (BPJ), applying it to a dataset from southern Chile, to determine the criteria proposed by 12 experts in assessing the status. The experts were provided with raw species abundance data, from 12 stations within a gradient of disturbance, from unaffected to severely affected. There was a very good agreement among experts (kappa values 0.72–0.77), with highly significant (p < 0.001) correlation between BPJ and AMBI and M-AMBI classifications, and an agreement of 76.4% and 81.9%, respectively. When comparing BPJ in Chile with other results in Europe, USA and northern Africa, similar patterns can be identified: (i) the number of criteria identified for classification is very high (range 7–12); (ii) the experts use several criteria together in the BPJ assessment; and (iii) the rank of the most important criteria is indicator species, richness, and diversity/dominance. These criteria are included in indices such as AMBI and M-AMBI. Hence, although experts are classifying samples subjectively when applying BPJ, they are corroborated in their opinions when using such indices. This fact can explain why these indices are so widely used.     

Waterbird communities along the estuarine salinity gradient of the Schelde estuary, NW-Europe

The zonation of non-breeding waterbirds along the Schelde estuary (The Netherlands–Belgium), one of the longest estuaries in NW-Europe with still a complete salinity gradient, including a large freshwater tidal area, was described. Numbers of birds were counted monthly over the period October 1991 to June 1997. Highest numbers of waterbirds were observed in late autumn and winter, with annual peak numbers ranging between 150,000 and 235,000 individuals for the whole estuary. Based on a multivariate analysis different waterbird communities were observed along the salinity gradient. The polyhaline areas of the estuary were numerically dominated by the waders Oystercatcher and Dunlin. Due to the presence of a large brackish marsh in the mesohaline zone, the waterbird community in this area was dominated by the herbivores Wigeon and Greylag Goose. In the oligohaline and freshwater tidal areas, the waterbird community was dominated by duck species, with Teal and Mallard being the most important. The international importance of the Schelde estuary for waterbirds was evidenced by the fact that for 21 waterbird species the 1% level criterion, according to the Ramsar convention, was exceeded. The relation of the observed diversity and community patterns with the functional and habitat diversity of the Schelde estuary as well as the effect of recent conservation measures to preserve this habitat were discussed.