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Understanding shifts in benthic communities along gradients over time is of crucial importance in estuarine ecology and for conservation. Yet studies considering historical data and both taxonomic and functional aspects are rare. We analysed data of macrobenthic invertebrates of the highly modified Elbe Estuary (Germany) from 1889, 1985, 1986 and 2006 to assess community shifts and considered both taxonomic and functional aspects. The number of species, functional richness (FRic) and functional redundancy (FR) reached minimum values in 1985 and 1986 and were highest and similar in 1889 and 2006. However, beta-diversity analysis showed that species assemblages in 1889 and 2006 greatly differed, almost exclusively owing to species replacement. Most striking was the decline in gastropods after 1889 to levels approaching extinction in the estuary in the other sampling years, most likely due to elevated concentrations of chemical substances, such as tributyl tin. Functional beta diversity was mainly a result of functional nestedness and was exceptionally low in a comparison of data from 1889 to 2006, which indicated nearly complete functional recovery. Null models revealed that function loss in 1985 and 1986 was non-random, consistent with habitat filtering. All functional groups were present on all sampling dates, which suggested that FR might have provided protection from significant ecosystem function loss. Our results indicate that FRic and FR in 1889 could have promoted ecosystem resilience and stability.

The estuarine maximum turbidity zone (MTZ) can be assumed to be a stressful environment featuring special conditions of great biological importance with an excess of organic matter, high-deposition rates, large variations in salinity, and dredging activities. Under such harsh conditions, populations may remain below the carrying capacity and competition is assumed to be of little importance, as predicted by the stress-gradient hypothesis. Therefore, we hypothesized that invertebrates of similar feeding types may utilize the same resources. To test our hypothesis, we chose the three most abundant taxa classified in literature as deposit feeders (Bathyporeia pilosa, Boccardiella ligerica, Marenzelleria sp.) and two taxa classified as predominately predacious (Palaemon longirostris, Crangon crangon) and determined their isotopic niches based on a stable isotope analysis for the MTZ of the Elbe Estuary (Germany). We expected the isotopic niches of similar feeding types to show a clear overlap if our hypothesis was true. Our results showed that the isotopic niches of no two taxa overlapped within each feeding group, indicating different resource use and the absence of competition. The sediment analysis revealed that two of the deposit feeders inhabited significantly different mean grain sizes. The lack of overlap of isotopic niches within each feeding group may be due to differences in habitat and feeding behavior in the case of the deposit feeders and due to different migration behavior in the case of the predominately predacious species. However, competition may have occurred in the past, resulting in a divergence of feeding niches during evolution.

Artificial substrates are omnipresent today in most estuaries mostly in form of massive rip-rap used for groynes and jetties. In the Weser estuary, Germany, 60% of the shoreline is covered with such artificial substrates while, natural rocky substrate is lacking, as in all Wadden Sea estuaries. This large quantity of artificial substrates may be colonized by a benthic hard-substrate community which differs from the local natural soft-substrate assemblage. In this study we examined species compositions, abundances, biomass, and numbers of species of subtidal benthic communities on groynes and in the natural habitat, the sediment, along the salinity gradient of the Weser estuary. Species composition changed on both substrates significantly with salinity and was also significantly different between the substrates. In a comparison with the sediment, the groynes did not provide any benefit for non-indigenous nor for endangered species in terms of abundance, biomass, and number of species, but represent habitats with higher total abundances and biomass; though some non-indigenous species even occurred exclusively on groynes. In particular, groynes supported filter-feeding organisms which play an important role by linking benthic and pelagic food webs. The dominance of the suspension feeders affects crucial estuarine ecosystem services and may have important implications for the estuarine management by altering the estuarine ecological quality status. Hence, artificial substrates should be considered in future conservation planning and in ecological quality monitoring of the benthic fauna according to the European Water Framework Directive.

The Venice System is one of the best-known and most applied systems to classify waters with respect to salinity. It has often been subject to criticism because the criteria used to derive zone boundaries were not made explicit. Consequently, an alternative multivariate PCA method that aimed at identifying salinity zones by means of the salinity ranges preferred by species was introduced by Bulger et al. (1993). We tested the applicability of both methods using salinity and benthic macroinvertebrate data for the poikilohaline Elbe Estuary (Germany) from 1997 to 2012. This was done by comparing the resultant salinity zone limits from the two approaches with boundaries where significant community changes were found by means of cluster analysis. Only the Venice System polyhaline and limnetic zone boundaries, and the PCA method outer estuary zone limit, showed good agreement with the benthic community pattern. None of the other Venice System or PCA method zone limits reflected the benthic community patterns. Our findings suggest that zone limits can only be well determined from mean salinity at the inner and outer end of the estuary, where the variation of salinity is relatively low. In contrast, in the middle of the estuary variation in salinity is the better predictor of zone boundaries. Thus, application of the Venice System or the PCA method in poikilohaline estuaries, such as the Elbe, is not meaningful and their use should be limited to homoiohaline systems. For poikilohaline systems, we found cluster analysis to be a better tool to identify salinity-zone boundaries.

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.

Summary 1. We assessed sex-specific seasonal changes in major energy storage compounds (triglycerides, glycogen) in Gammarus fossarum and Gammarus pulex collected from the field, with respect to their reproductive activity. 2. The dynamics of stored energy followed a seasonal pattern in both species and sexes. Moreover, over a 4-year period, these changes were independent of the year in which they were investigated. Stored energy reached a peak in late winter, but was depleted in late summer and early autumn, coinciding with the reproductive periods. 3. Triglyceride (annual mean ± SD) accounted for 79.7 ± 11.9% of the total stored energy and was responsible for the seasonal pattern. In contrast, glycogen contributed a lesser percentage (20.3 ± 11.9%). Over the study period, the amount of stored energy ranged between 0.39 and 4.08 kJ g−1 dry mass (triglyceride: 0.19–3.69 kJ g−1 dry mass; glycogen: 0.14–0.80 kJ g−1 dry mass). 4. In both species, the energy reserves of males were drastically depleted shortly before the cessation of precopulatory mate guarding in the field, thus offering a bioenergetic explanation for the reproductive period in these two widespread species.

Purpose Acute whole-sediment bioassay with the estuarine and marine amphipod Corophium volutator (Pallas) is widely used to assess toxicity of sediments. According to the guidelines DIN EN ISO 16712, mortality is the determined toxic endpoint. Additionally, the reburrowing ability of the surviving organisms of this acute toxicity test in fresh uncontaminated sediment is suggested as the sublethal endpoint, but insufficient information (e.g., exact measurement protocols) on this endpoint is provided, thus confounding factors and the interpretation of the results. The aim of this study was to provide information on burrowing activity as a sublethal endpoint.

Indices to assess the ecological status of water bodies according to the European Water Framework Directive (WFD) frequently produce widely differing results when applied to estuarine systems. Although several ecological indices have been employed to coastal environments and in estuaries in particular, there is still a lack of knowledge about their suitability for assessing the ecological status of heavily modified water bodies. Thus, we evaluated the performances of indices and fauna parameters (AMBI, M-AMBI, BOPA, BO2A, W-value, Shannon diversity, species richness, abundance) that have been discussed in the WFD context using data on invertebrates dwelling in two typical morphological units: the navigation channel and the river bank habitats of Elbe estuary (Germany). In addition, we tested their ability to identify several environmental factors (grain size distribution and chemical sediment contamination). All indices were able to detect major changes in macrofauna composition along the estuarine salinity gradient and were able to differentiate between navigation channel and shallow bank habitats. A strong significant correlation was found with most indices with the exceptions of the W-value and the BOPA with mean grain size. Almost all indices signaled poor ecological quality in the coarser fairway sediments against the finer sublitoral bank sediments. However, AMBI and BOPA showed the opposite: both indicators classified the invertebrate assemblages from the navigation channel better compare than the shallower habitats. The correlation of ecological indices and parameters with sediment contaminants and the toxicity of the sediment calculated as toxic units showed a diverse picture: all indices, except species richness and the BOPA, had a certain significant correlation with several individual sediment pollutants, however, only one index, the W-value, was correlated significant with the majority of chemical pollutants (Pb, Cd, Cu, Ni, Hg, Zn, β-HCH, pp′-DDD, and TBT) and the toxic units. Our results show clearly that ecological quality classification of heavily modified estuaries depends strongly on both the index and the habitat. Thus, we conclude that no index should be used on its own to estimate the ecological quality of estuaries. Further investigations and the improvement or development of such indices should place emphasis on their independence from the grain size spectrum of the sediments and on their good correlation with its pollution status.

Geotextile materials find increasing use in coastal protection as an alternative material to natural stone, slag, and concrete. In this environment geotextiles, like all surfaces of technical objects immersed in seawater, are subject to accumulation of organisms on their surfaces, a process usually called biofouling. In a 2-year experiment we investigated the colonization of benthic organisms on two different geotextile materials (woven fabric and non-woven fabric) in the Elbe estuary, Germany, and compared it with the colonization on unglazed ceramic tiles as reference representing the nearest compromise to natural hard substrates. Then, non-woven fabric was colonized by significantly less species, fewer individuals, and lower biomass values than the woven fabric and the ceramic tiles (one-factor ANOVA, p t -test, p ≥ 0.05), while the biomass was still increasing significantly on all materials ( t -test, p t -test p ≥ 0.05). Geotextile materials therefore offer a unique choice in coastal and hydraulic engineering: depending on the application, engineers can choose between a material that is easily colonized by benthic species, or one that minimizes such colonization where it is undesired.

Nepenthes madagascariensis is a carnivorous plant which captures its prey in pitcher-like leaves. It is endemic to Madagascar where it occurs along the eastern coast. Altogether 94.3% of its prey animals belong to three taxa: Formicidae (80.2%), Diptera (9.7%) and Coleoptera (4.4%). The prey compositions of the dimorphic lower and upper pitcher types differ significantly, especially in the markedly higher proportion of ants in lower pitchers and the higher number of flying insects in upper pitchers. A comparison concerning the trap frequency of taxa with literature data from Asian Nepenthes species showed that the upper pitchers of N. madagascariensis contained much higher proportions of Coleoptera, Diptera and Lepidoptera; these differences may partly be due to seasonal reasons. No significant correlation could be established between the numbers of prey items with pitcher size. This paper is the first characterization of the prey composition of the little known N. madagascariensis.

Defining the reference condition is one of the most critical aspects of ecosystem investigations since it describes the baseline against which the experimental sites will be evaluated and compared. In large-scale ecosystem experiments, this reference is ideally another ecosystem which is similar to the experimental system. We investigated two streams for their potential as experimental sites for a full-size pairwise ecosystem experiment. Temporal (2 years) and spatial (pool, riffle) variabilities of abiotic factors and as biotic element the structure of the macroinvertebrate communities were investigated. Criteria of similarity that we applied at the two streams were: (1) high similarity in abiotic factors, (2) only small differences in the faunal assemblages (abundance structures, composition, feeding types), and (3) that the differences between the two systems should not exceed the temporal and spatial differences within each system. Among the abiotic factors investigated, only the inorganic nutrients (nitrate and soluble reactive phosphorus), major ions (magnesium, calcium), electric conductivity, and pH showed significant differences between the two streams. Discharge rate, current velocity, temperature, and oxygen concentrations did not significantly differ between the streams. Also, the community structure did not differ in species richness, abundance, and biomass; and only small differences in dominance structure and feeding-type composition were observed. The differences between habitats within each stream were always higher than those between the streams. Thus, both the streams are characterized by a similar structure of the macroinvertebrate community, a main component of the stream food-web, which make them suitable for a full size pairwise ecosystem experiment. The present case study can form a basis for other full-size field experiments.

The Ponto-Caspian amphipod Dikerogammarus villosus is one of the most successful invaders in Central European rivers. Contrary to studies on its ecology, ecophysiological studies comparing the species' physiological traits are scarce. In this context, in particular the metabolic activity of the invasive species has rarely been considered and, moreover, the few existing studies on this species report strongly deviating results. The purpose of this study was to assess the metabolic activity and behavior of D. villosus and other common European amphipod species (Gammarus fossarum, Gammarus roeselii) in relation to temperatures covering the thermal regime of the invaded habitats. Based on direct calorimetric measurements of metabolic heat dissipation at three temperature levels (5°C, 15°C and 25°C), we found the routine metabolic rate of D. villosus to be significantly lower than that of the other studied gammarid species at the medium temperature level. The estimated resting metabolic rate indicated a similar trend. At 5°C and 25°C, both routine and resting metabolic rate did not differ between species. Compared to G. fossarum and G. roeselii, D. villosus exhibited lower locomotor activity at the low and medium temperatures (5°C and 15°C). In contrast, its locomotor activity increased at the high experimental temperature (25°C). G. fossarum and G. roeselii were apparently more active than D. villosus at all studied temperatures. We conclude that D. villosus has both physiological and behavioral adaptations that lead to a reduction in metabolic energy expenditure, which is assumed to be beneficial and might contribute to its invasive success.

Two preservative treatments traditionally used in aquatic sciences, formalin (4%) and ethanol (70%), were compared for their effects on biomass estimations. The effects of both preservatives on wet weight, dry weight, and ash-free dry weight were determined for samples preserved for 10, 21, and 90 days. The effects were studied in four different macrofauna species commonly found in German estuaries: Heteromastus filiformis (Capitellidae, Polychaeta), Hediste diversicolor (Nereididae, Polychaeta), Corophium sp. (Amphipoda, Crustaceae), and Gammarus spp. (Amphipoda, Crustacea). The biomass estimates of preserved samples were compared with those of unpreserved samples. In all four species the loss in wet weight, dry weight, and ash-free dry weight was most pronounced within the first 10 days, and an additional weight loss was recorded between days 10 and 21. However, there was no further loss in weight for samples kept for as long as 90 days in the preservatives. In general, crustaceans exhibited higher weight loss than polychaetes, and smaller species (H. filiformis and Corophium sp.) showed higher weight loss and a higher variability than larger species. As our main result, significant differences between the two preservative treatments did never occur. Our results contradict some earlier investigations on this matter where formalin has been reported to be superior to alcoholic preservatives because weight loss was less pronounced than in ethanol. Factors affecting biomass estimates are discussed and we conclude that, for the macrofauna groups tested, the use of the toxic formalin solution is not justified when the major intent is biomass estimation.

The development of an epilithic nematode community and the mode of colonisation was monitored over a 57-day period during spring in a field experiment in the littoral zone of a large oligotrophic lake. Two types of experimental units were used: one type prohibited direct colonisation via active crawling by elevating substrates into the water column and the second type had substrates placed on the lake bottom. Data from the two types of units and from nearby natural hard substrates were compared. The nematodes quickly colonised on the introduced substrates and reached maximum densities of 123 individuals per 10 cm2 after 57 days. Nematode densities on elevated and non-elevated substrates did not differ significantly. The nematode abundance and community structure showed a large initial variation, but became more stable over time and resembled the natural community structure at the end of the experiment. The maximum number of nematode species was reached after 2 weeks of colonisation, with a maximum species number on days 12 and 14 in the experimental units and on day 19 on the surrounding natural hard substrates. The five numerically dominant species, Eumonhystera vulgaris, Chromadorina bioculata, Eumonhystera filiformis, Chromadorina viridis and Daptonema dubium, accounted for most of the variation between the different communities. The results indicate that water-column transport was the main colonisation pathway of epilithic nematodes. The distribution of nematode species points to potential morphological adaptations of some species for persistence on hard substrates.

Meiofauna are known to live on hard substrates in association with periphytic and epiphytic algae and attached epibiota; however, the abundance, diversity and colonizing abilities of hard-substrate meiofauna have been poorly documented. We quantified meiofauna living on microalgal-covered pilings associated with a wood pier in a shallow (

The European Water Framework Directive (WFD) requires a status assessment of all water bodies. If that status is deteriorated, the WFD urges the identification of its potential causes in order to be able to suggest appropriate management measures. The instrument of investigative monitoring allows for such identification, provided that appropriate tools are available to link the observed effects to causative stressors, while unravelling confounding factors. In this chapter, the state of the art of status and causal pathway assessment is described for the major stressors responsible for the deterioration of European water bodies, i.e. toxicity, acidification, salinisation, eutrophication and oxygen depletion, parasites and pathogens, invasive alien species, hydromorphological degradation, changing water levels as well as sediments and suspended matter. For each stressor, an extensive description of the potential effects on the ecological status is given. Secondly, stressor-specific abiotic and biotic indicators are described that allow for a first indication of probable causes, based on the assessment of available monitoring data. Subsequently, more advanced tools for site-specific confirmation of stressors at hand are discussed. Finally, the local status assessments are put into the perspective of the risk for downstream stretches in order to be able to prioritise stressors and to be able to select appropriate measures for mitigation of the risks resulting from these stressors.

The concentrations of the butyltin (BT) species tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were measured in the surface sediments (0-20 cm) at 29 sites of the Elbe estuary in 2011. TBT values ranged from 'undetectable' to 41 ng Sn g(-1) dry weight (d.w.) with the two highest values measured in the inner section of the estuary near the port of Hamburg (32 and 41 ng Sn g(-1) d.w.). TBT, DBT, and MBT showed significant decreases towards the estuarine mouth (Spearman's rho -0.660, -0.685, and -0.583, respectively, p

Sediment contamination is one of the most pressing environmental problems in estuaries of industrialized countries and is of special interest to water managers involved in waterway maintenance dredging. In the present study, eight heavy metals (As, Pb, Cd, Cr, Cu, Ni, Hg, and Zn) and 41 organic compounds (pentachlorbenzol (PeCB), hexachlorbenzol (HCB), 7 polychlorinated biphenyls (PCBs), the hexachlorocyclohexanes α-HCH, β-HCH, γ-HCH, 6 dichlorodiphenyltrichloroethane isomers, organochlorine styrene (OCS), octachloronaphthalene (OCN), 15 polycyclic aromatic hydrocarbons (PAHs), and 6 organotin (OT) compounds) were analyzed in surface sediments at 36 sites in the Elbe estuary in 2006. Correlation analysis showed a general decrease in sediment contaminant concentrations from the stations near the port of Hamburg towards the open sea. This decrease was significant (Spearman's rank correlation, p0.05) with most pollutants. In addition, cluster analysis identified five groups of sites with different sediment contaminant patterns within the Elbe estuary. Worst case toxic risks stemming from sediment-bound organic pollutants were predicted using the Toxic Unit approach, based on estimated pore-water concentrations under equilibrium conditions and acute LC50 values for three standard test organisms of the trophic levels of fish, invertebrates, and algae. The estimated sediment toxicity was significantly higher in the inner part (river-km 630 to 660) compared with the estuarine mouth. Moreover, potential toxicity of organic pollutants estimated for invertebrates and for fish exceeded acute-based effect thresholds at 30 and 24 stations, respectively. Chronic effects for invertebrates are expected at all sites investigated. We conclude that sediment pollution and related potential toxicity in the Elbe estuary may have more influence on the benthos fauna than expected to date.