Diet of two invading gobiid species (Proterorhinus semilunaris and Neogobius melanostomus) during the breeding and hatching season: No field evidence of extensive predation on fish eggs and fry

One of the potential impacts of invasive gobies on native fish fauna is predation on eggs and fry. Therefore, the diet composition of two invading gobiid species, the tubenose goby Proterorhinus semilunaris and round goby Neogobius melanostomus, was examined in the Dyje river system (Danube basin, Central Europe) during the 2011 reproductive season to ascertain the extent of gobiid predation on heterospecific and conspecific eggs and juveniles. Consumption of fish eggs and juveniles by invading gobies was very low. The diets of both species consisted largely of benthic macroinvertebrates, and particularly insect larvae. These results indicate that invading gobies in the Dyje river system are likely to impact native fish fauna more through competitive effects than through direct predation on eggs and juveniles.     

Impact of reservoirs and channelization on lowland river macroinvertebrates: A case study from Central Europe

In order to assess and compare the ecological impacts of channelization and shallow lowland reservoirs, macroinvertebrate communities of a lowland metapotamal river below reservoirs with epilimnial release were studied. The study was carried out in the Dyje River (Czech Republic) at five sites located from 1.5 to 22.5 km downstream of the reservoir outfall. The five sites differed in the degree of channel modification from natural muddy banks to riprap regulation. Seven samples were collected during the years 1998 and 1999 at each site using a semiquantitative method. The data were processed using multivariate analyses and methods for assessing the ecological and functional structure of communities. Altogether, 261 species of benthic macroinvertebrates were recorded including several rare and threatened taxa. Based on the results of principal component analysis (PCA), most of the variability within the species data (the first PCA axis) was explained by the degree of channel modification, from natural muddy banks with aquatic vegetation to a man-made riprap. The second axis was strongly correlated with current velocity. The sites differed in species richness, total abundances, proportion of individual functional feeding groups, pattern of the distribution of the current preference groups, and values of several biotic indexes, all of which also corresponded to the degree of channel modification. Thus, the morphological man-made modifications of the river channel were found to be the main factor affecting lowland river macroinvertebrates and their biodiversity. Our results suggest that the biggest threat to benthic macroinvertebrate diversity of lowland rivers comes from channelization. The impact of reservoirs can be completely overwhelmed by the impact of channelization, especially when muddy banks with aquatic vegetation present a substantial part of habitat diversity and significantly contribute to the total species pool.     

Chironomid diversity in the diets of Ponto-Caspian gobiids in a freshwater habitat: Implications for resource partitioning

Chironomid taxa in the diets of six co-occurring gobiids (Caucasian dwarf goby Knipowitschia caucasica; monkey goby, Neogobius fluviatilis; racer goby, Babka gymnotrachelus; round goby, Neogobius melanostomus; bighead goby, Ponticola kessleri; and western tubenose goby, Proterorhinus semilunaris) were investigated in a freshwater habitat in Ukraine. Overall, 32 chironomid morphotypes were identified, among which the most abundant were Polypedilum convictum, Cricotopus sylvestris, Glyptotendipes spp., and Endochironomus albipennis. The racer and monkey gobies were characterized by the highest diversity of chironomid morphotypes in their diets, while the bighead goby by the lowest diversity. Highest similarities of chironomid assemblages in gut contents were observed among the monkey, racer, and round gobies as well as between the bighead and tubenose gobies, while the lowest similarity was observed between the monkey goby and Caucasian dwarf, tubenose, and bighead gobies. Mean sizes of chironomids in the gut contents of different gobiids varied; Caucasian dwarf and tubenose gobies consumed significantly smaller chironomids. Diversity of chironomid taxa in the diets of gobies depended on the type of each fishes’ habitat. Tubenose and bighead gobies preyed mainly on phytophilous chironomids; the monkey and round gobies preferred bottom-dwelling, burrowing chironomids; while Caucasian dwarf and racer gobies consumed both phytophilous and bottom-dwelling, burrowing taxa.     

鳑鲏与河蚌交互作用对浮游生物和底栖生物的影响分析

放养河蚌,提高水体透明度以促进沉水植物生长,是湖泊生态修复中的常用手段之一.而小型杂食性鱼类鳑鲏依赖河蚌繁殖,河蚌放养可能会促进鳑鲏种群的发展;而鳑鲏与河蚌交互作用对水生态系统的影响仍研究较少.于2018年11-12月通过原位受控实验,设置对照组、河蚌组、鳑鲏组和河蚌+鳑鲏组,研究了鳑鲏(大鳍鱊Acheilognath...     

Diet and feeding strategies of round goby,Neogobius melanostomus (Pallas, 1814) from the invasion front in the Danube River tributaries (Bulgaria): ontogenetic shift and seasonal variation

The round goby Neogobius melanostomus is one of the most successful Ponto-Caspian fish invaders, established in a variety of aquatic ecosystems throughout Europe and North America. Diet and feeding strategies of N. melanostomus from three recently invaded tributaries of the Lower Danube River (Bulgaria) were investigated. Research design is based on monthly examination of the round goby diet and macroinvertebrate density. The results show that the round goby consume a wide range of different organisms – 76 taxa in total (identified to family, genus or species level). The most common prey taxa in all three rivers were Chironomidae (Orthocladius/Cricotopus spp., Tanytarsini g. sp.), Trichoptera larvae (Psychomyiidae g. sp., Hydropsyche spp.) and Ephemeroptera nymphs (Baetis spp.). Only in one of the rivers, a predominant feeding on crustaceans (Gammarus spp.) was observed. The taxonomical composition of consumed invertebrates suggests that the round goby prefers the ecological group of “sprawling/walking” insect larvae associated to coarse substratum. Feeding activity was observed throughout the whole year, even during low-temperature months. Three seasonal and four size-depended shifts in the species’ diet were determined. Generalization feeding tactics predominated in all three rivers. Specialization was rare and specific for each tributary, where a few individuals consumed invertebrates from fine substratum and/or submerged vegetation. Possible relationships between the spread of N. melanostomus and the recent invasion of the Asian clam (Corbicula fluminea) in the Bulgarian Danube tributaries were discussed. Generalisation and feeding plasticity contribute to the round goby’s establishment success in the Danube tributaries and might facilitate its further upstream spread.     

Reproductive strategies of three invasive Gobiidae co-occurring in the Lower Rhine (Germany)

At the Lower Rhine, three congeneric, invasive Gobiidae constitute the major part of local fish assemblages. Reproduction strategies play an important role in biological invasion processes and help to predict future population development. Up to now, studies on the reproductive traits of the three species have led to contradictory findings in invaded areas, and studies on native populations are scarce, especially when regarding a co-occurrence of the three species. This study provides an overview over already existing knowledge of reproductive traits in native as well as invaded regions and describes the reproduction modes of all three species at the Lower Rhine. Based on intensive beach seine sampling in nursery habitats for three consecutive years, detailed information about the spawning habits of the bighead goby Ponticola kessleri, the round goby Neogobius melanostomus, and the monkey goby N. fluviatilis is provided. Spawning onset as well as length and intensity of the spawning season were determined by estimating growth rates and subsequent back-calculations of hatching and spawning events. Gonadosomatic index (GSI) analyses of adult gobies were used to cross-validate results and to assess validity of the used method. Growth rates for the first three months of all three species were highly variable and ranged between 0.3 mm and 0.95 mm total length per day. All three Gobiidae displayed different reproductive modes with bighead gobies spawning first in March/April, but probably only once a season. In contrast, round and monkey gobies started reproducing slightly later, but then continued spawning throughout the season until September, exhibiting temporal separation with varying intensities. High variation in spawning onset, length and reproductive output for all three species was observed over the years and no relationship between spawning onset and temperature could be detected. For the first time, highly resolvent information on spawning onset and spawning season length is obtained and the fine-tuned differences between the three species are highlighted.     

Dams in the last large free-flowing rivers of Patagonia,the Santa Cruz River,environmental features,and macroinvertebrate community

Three large rivers have their headwaters in the Patagonian Ice Fields (PIFs) in the Andes Mountains, the largest mid-latitude ice masses on Earth: Santa Cruz, Baker and Pascua. They are the last large free flowing rivers in Patagonia, but plans are advanced for building dams for hydroelectric power generation. The three PIF rivers, with a discharge dominated by ice melt, share a common, unique hydrograph compared to that of the other eight large rivers in the region: a distinct seasonal cycle, and an extremely stable discharge, with much lower variability than other rivers. In this study we present the first extensive survey of habitats and benthic macroinvertebrates in the least studied system, the Santa Cruz River. We assess how much of the natural capital provided and sustained by benthic invertebrates are expected to be lost by flooding and discuss how dams would affect riverine habitat and biota. In the Santa Cruz River, we conducted an intensive field survey during September 2010; a total of 52 sites located at regular 6 km intervals were sampled along the 310 river-km for macroinvertebrates and seventeen habitat variables. Although some habitat structure is apparent at the local scale, the Santa Cruz River could be described as very homogeneous. Macroinvertebrate density and the richness (38 genera) found in the Santa Cruz River resulted to be one of the lowest in comparison with 42 other Patagonian rivers. Albeit weak, the structure of the macroinvertebrates assemblages was successfully described by a reduced set of variables. The reduced flow variation and the lack of bed scouring flows have a direct and negative effect on the heterogeneity of riverbeds and banks. The high turbidity of the Santa Cruz River may also contribute to shorter food webs, by affecting autotrophic production, general trophic structure, and overall macroinvertebrate productivity and diversity. Dams will obliterate 51% of the lotic environment, including the most productive sections of the river according to our macroinvertebrate data. Since Santa Cruz River has a naturally homogeneous flow cycle, dams may provide more variable flows and more diverse habitat. Our data provide critically valuable baseline information to understand the effects of dams on the unique set of glacial driven large rivers of Patagonia.     

Biodiversity loss in benthic macroinfaunal communities and its consequence for organic mercury trophic availability to benthivorous predators in the lower Hudson River estuary, USA

Organic mercury such as methylmercury is not only one of the most toxic substances found in coastal ecosystems but also has high trophic transfer efficiency. In this study, we examined implications of chronically altered benthic macroinfaunal assemblages for organic mercury trophic availability (based on organic mercury intracellular partitioning) to their predators in the Arthur Kill-AK (New York, USA). Despite low species diversity, both density and biomass of benthic macroinvertebrates in AK were significantly higher than those at the reference site. Disproportionately high biomass of benthic macroinvertebrates (mostly polychaetes) in the northern AK resulted in a more than twofold increase (‘ecological enrichment’) in the trophically available organic mercury pool. These results suggest that altered benthic macroinfaunal community structure in AK may play an important role in organic mercury trophic availability at the base of benthic food webs and potentially in mercury biogeochemical cycling in this severely urbanized coastal ecosystem.     

Flow field-induced drag forces and swimming behavior of three benthic fish species

Modern ethohydraulics is the study of the behavioral responses of swimming fish to flow fields. However, the exact drag forces experienced by fish remain poorly studied; this information is required to obtain a better understanding of the behavioral responses of fish and their current resistance strategies. We measured near-ground frontal drag forces on preserved individuals of three benthic fish species, round goby (Neogobius melanstomus), gudgeon (Gobio gobio) and bullhead (Cottus gobio), in a flow channel. The forces were compared to acoustic Doppler velocity (ADV) measurements and fish tracking data based on video observations of live fish in the flow channel. Overall, we observed drag coefficients (C_D) of ∼10⁻³ at Reynolds numbers ∼10⁵. The frontal drag forces acting on preserved fish with non-spread fins ranged from -1.96 mN*g^-1 (force per fish wet weight, velocity 0.55 m*s^-1) to 11.01 mN*g^-1 (velocity 0.85 m*s^-1). Spreading the fins strongly increased the drag forces for bullhead and round goby. In contrast, the drag forces were similar for gudgeon with spread fins and all fish with non-spread fins. Video tracking revealed no clear relationship between the position of the fish in the flow field and the forces experienced by the preserved fish at these positions. Collectively, these results suggest that i) the differences in frontal drag forces between species are small in homogenous flow, ii) individuals chose their position in the flow field based on factors other than the drag forces experienced, and iii) whether fins are spread or non-spread is an essential quality that modulates species-specific differences. The methodology and results of this study will enable integration of flow measurements, fish behavior and force measurements and inform ethohydraulics research. More advanced force measurements will lead to a detailed understanding of the current resistance strategies of benthic fish and improve the design of fish passes.     

Expansion of round gobies in a non-navigable river system

A number of Ponto-Caspian Gobiid species have greatly increased their geographical ranges over recent decades. Most expansion studies to date, however, have focused on navigable waterways. In this study, we present a summary of six-years (2008–2013) monitoring of round goby Neogobius melanostomus expansion along two connected non-navigable rivers. Contiguous range expansion was observed in both rivers, with dispersal rate ranging from 1.2 to 3.2 km/year. Gobies at newly invaded sites ranged from 20 to 117 mm, with both juveniles and adult fish observed. Though the data did not allow us to see any consistent pattern in the first years after detection, there was some evidence for a shift to a female-biased, juvenile-dominated population over time. While the abundance of non-native tubenose goby Proterorhinus semilunaris appeared to be negatively influenced by round goby establishment, diversity of nearshore native fish showed no evidence of dramatic decline attributable to round goby.     

Development of benthic macroinvertebrates sediment index(BSI) for bioassessment of freshwater sediment

Sediment quality has been evaluated in a variety of ways since the early 1990s in studies from Europe. In South Korea, most studies have used an indicator value for benthic macroinvertebrates based on water quality, not sediment quality. To date, few studies have examined the biological integrity of benthic macroinvertebrate communities in South Korea. In the current study, the tolerance valency and value in samples and the indicator weight values were measured for 43 benthic macroinvertebrate taxa from 73 sampling units in South Korea from 2014 to 2016. Total organic carbon, the amount of heavy metals, and total ammonia nitrogen were analyzed. The average grade for each pollutant was used as the sediment quality index. A benthic macroinvertebrates sediment index was developed for bioassessment of freshwater sediment. The benthic macroinvertebrates sediment index, which is based on the relative frequency of occurrence of macroinvertebrates, was highly correlated with pollution levels in the sediment. This index can be used in the field to assess the contamination of freshwater sediment. As the sample size was small in the current study and there were taxonomic limitations of Chironomidae larvae, further research is needed to improve the reliability of the benthic macroinvertebrates sediment index.     

Autecology of Limnomysis benedeni Czerniavsky, 1882 (Crustacea: Mysida) in Lake Constance, Southwestern Germany

The Ponto-Caspian mysid Limnomysis benedeni was first recorded in Lake Constance in summer 2006, and a stable population developed at the site of discovery. Although this mysid is common in the Rhine and Danube rivers, little is known about its ecology and impact in systems of invasion. We investigated the autecology of L. benedeni in habitat-choice and food experiments. In the habitat-choice experiments, highly structured habitats, i.e., stones covered with zebra mussels (Dreissena polymorpha), macrophytes, and especially stonewort, were strongly preferred. In food experiments, L. benedeni fed mostly on food sources with a small particle size, e.g., biofilm on leaf litter, biodeposited material of zebra mussels, epilithon, and phytoplankton. We also compared the L. benedeni population data from Lake Constance with that from rivers. In Lake Constance, female L. benedeni were nearly 30% larger and carried more than three times more eggs in spring (9.4±0.6 mm and 28.4±5.7 eggs) than in summer (6.7±0.8 mm and 8.7±2.9 eggs). The mysids present in spring might be the generation that over-wintered; in summer, this generation was probably replaced by a new generation of smaller individuals. The large brood size and the detritivorous feeding strategy might allow L. benedeni to colonize Lake Constance rapidly.     

A River Water Quality Model for Chlorophyll and Dissolved Oxygen that Accommodates Zebra Mussel Metabolism

The development, testing and application of a dynamic two-dimensional (longitudinal-vertical) mass balance model for dissolved oxygen (DO) and chlorophyll (Chl) for rivers is documented that for the first time accommodates both the oxygen demand and filtering effects of zebra mussels. The test system is a phytoplankton-rich section ( 15 km long) of the Seneca River, NY, that is believed to represent an upper bound of the impact of this exotic invader. Changes in common measures of water quality of the river brought about by the zebra mussel invasion are reviewed and related longitudinal patterns in DO, Chl, and Secchi disc transparency are documented. Model testing is supported by comprehensive measurements of DO, Chl, and various forcing conditions over a three-month period, and independent determinations of several model coefficients. Wide variations in the areal consumption rate of DO (ZOD; g·m^–2·d^–1) and filtering rate (m³·m^–2·d^–1) of zebra mussels, as determined through model calibration, occurred over the study period. Values of ZOD in areas with dense zebra mussel populations at times (e.g., > 50 g·m^–2·d^–1) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The value of determinations of these fluxes from model calibration procedures is evaluated within the context of the limitations of protocols presently available to support independent specification of these rates. Model analyses are conducted to evaluate the relative magnitude of source and sink processes for DO and Chl, the potential operation and implications of feedback from low DO levels on oxygen consumption by zebra mussels, and the sensitivity of model simulations to selected sources of uncertainty and variability. Model projections of oxygen resources of the river are presented in a probabilistic format in evaluating reductions in zebra mussel biomass that would be necessary to eliminate violations of standards and regain assimilative capacity.     

Interspecific competition for a shelter between non-native racer goby and native European bullhead under experimental conditions – Effects of season,fish size and light conditions

Under laboratory conditions, we assessed by video-recorder whether or not the interference competition of invading racer goby Babka gymnotrachelus affects the habitat (refuge) use and behaviour of European bullhead Cottus gobio, a native nest-guarding species, during and after the spawning season, spring and autumn respectively, when available refuge (nesting) habitat is limited. A bullhead was placed in a tank for 24 h and then an intruder, either a goby or another bullhead was added for the next 24 h. We assessed: (1) the time spent by the two fish in the shelter; and (2) acts of aggression and attempts to enter the shelter. In spring, the amount of time spent in the shelter by the bullhead was considerably lower in the presence of a racer goby of larger or equal size than when the bullhead was alone. In autumn, bullheads occupied shelters at a similar frequency with and without a goby present. Smaller gobies were not able to replace bullhead residents in the shelter. Racer gobies were much more aggressive than bullheads of equal or smaller size, particularly in spring. Bullheads kept outside of the shelter by a resident goby made more attempts to enter the refuge during spring. In summary, under experimental conditions, racer gobies modified the typical behaviour of bullheads by reducing the use of shelter and potential nesting places.     

Benthic respiration and stoichiometry of regenerated nutrients in lake sediments with Dreissena polymorpha

The effect of patchy colonies of the invasive zebra mussel (Dreissena polymorpha) on sedimentary processes was investigated in a mesotrophic lake (Plateliai Lake, Lithuania). Benthic fluxes of O₂, TCO₂, CH₄, Mn²⁺, Fe²⁺, N₂, the inorganic forms of N, Si and P and dissolved organic C and N were quantified by dark incubations of sediments cores, with and without D. polymorpha. Individual mussels also were incubated for metabolic measurements. Sediments with D. polymorpha had significantly higher O₂ and TCO₂ fluxes and displayed higher rates of denitrification. The presence of mussels also resulted in higher regeneration of P and N (mostly as ammonium) while the effect on Si was not significant. However, likely due to the low zebra mussel biomass (57.2 ± 25.3 g_SFDW m^?2), biodeposition has not changed the ratio between anaerobic and total respiration. Methane and reduced metals fluxes were in fact similar in the presence and absence of D. polymorpha. Incubations of mussels without sediments confirmed that bivalve metabolism was the main driver of benthic respiration and nutrient recycling. Nitrate production suggested the presence of nitrifiers associated with the molluscs. The main outcome of this study was that zebra mussels alter the quantity and the stoichiometry of nutrients regenerated by the benthic compartment. The enhancement of nitrogen loss via denitrification, by a factor of 1.5, was much less pronounced than the increase in ammonium recycling rate, stimulated by a factor of 33. Negligible PO₄ ^3? fluxes in bare sediments (?3.4 ± 6.8 μmol m^?2 h^?1) increased in the presence of mussels and considerable amounts of this nutrient (69.6 ± 29.4 μmol m^?2 h^?1) were mobilized to the water column. Further research should address other nutrient sources to the lake to verify whether altered rates and stoichiometry of benthic regeneration can affect primary producer community composition and activity.     

Fish predation on sympatric and allopatric prey—A case study of Ponto-Caspian gobies,European bullhead and amphipods

Due to the increasing number of biological invasions, more and more non-native species become components of already existing food chains and new interactions develop within communities. In our study, we checked whether (1) the predation preferences depended on sympatric or allopatric occurrence of predator and prey (a predator may choose the well-known prey or rather benefit from the naïvety of the novel one) and (2) fish preferences depended on prey susceptibility to fish predation (ability to hide, active predator avoidance) and/or on its palatability. We studied foraging efficiency of two species of Ponto-Caspian gobies (the round goby Neogobius melanostomus and tubenose goby Proterorhinus semilunaris) and the European bullhead Cottus gobio on two species of amphipods—Ponto-Caspian Dikerogammarus villosus and non-invasive Gammarus fossarum, occurring in Central and Western Europe. The gammarids were offered to fish with or without shelters and as mobile individuals or immobilized to test the effect of their hiding ability, mobility and palatability on fish predation. Fish selectivity was exhibited only in trials with motile prey, where all tested predators preferred G. fossarum over D. villosus, showing that their selectivity was independent of prey origin. No selectivity was observed for immobilized amphipods. When shelters were present, the predation was lowest. Thus, predator preferences depended on prey behavioural traits (effective shelter utilization and/or activity reduction) rather than on their palatability. Effective predator preference of G. fossarum over D. villosus may be one of the reasons of the successful invasion of the latter to the European inland waters.     

Heavy metal transport in large river systems: heavy metal emissions and loads in the Rhine and Elbe river basins

Pollutant transport and management in the Rhine and Elbe basins is still of international concern, since certain target levels set by the international committees for protection of both rivers have not been reached. The analysis of the chain of emissions of point and diffuse sources to river loads will provide policy makers with a tool for effective management of river basins. The analysis of large river basins such as the Elbe and Rhine requires information on the spatial and temporal characteristics of both emissions and physical information of the entire river basin. In this paper, an analysis has been made of heavy metal emissions from various point and diffuse sources in the Rhine and Elbe drainage areas. Different point and diffuse pathways are considered in the model, such as inputs from industry, wastewater treatment plants, urban areas, erosion, groundwater, atmospheric deposition, tile drainage, and runoff. In most cases the measured heavy metal loads at monitoring stations are lower than the sum of the heavy metal emissions. This behaviour in large river systems can largely be explained by retention processes (e.g. sedimentation) and is dependent on the specific runoff of a catchment. Independent of the method used to estimate emissions, the source apportionment analysis of observed loads was used to determine the share of point and diffuse sources in the heavy metal load at a monitoring station by establishing a discharge dependency. The results from both the emission analysis and the source apportionment analysis of observed loads were compared and gave similar results. Between 51% (for Hg) and 74% (for Pb) of the total transport in the Elbe basin is supplied by inputs from diffuse sources. In the Rhine basin diffuse source inputs dominate the total transport and deliver more than 70% of the total transport. The diffuse hydrological pathways with the highest share are erosion and urban areas. Copyright © 2002 John Wiley & Sons, Ltd.     

The impact of pelagic (Daphnia longispina) and benthic (Dreissena polymorpha) filter feeders on chlorophyll and nutrient concentration

An outdoor experiment testing the effect of water flea (Daphnia longispina) and zebra mussels (Dreissena polymorpha) on physical and chemical water parameters and chlorophyll concentration changes was carried out in 12 containers filled with 150 l of unfiltered water from a lowland reservoir. During the 11 weeks of the experiment, the following physical, chemical and biological measurements were recorded: temperature (°C), oxygen concentration (mg dm⁻³), pH, conductivity (S cm⁻¹), concentration of phosphate phosphorus (PO₄-P) and ammonia nitrogen (NH₄-N) (g dm⁻³), total nitrogen (TN) and total phosphorus (TP) (g dm⁻³), phytoplankton community structure and chlorophyll a concentration (g dm⁻³). The amount of ammonia ions was the highest in the treatment with zooplankton, while phosphate ions reached the highest values in treatments with zebra mussels. The results confirmed the ability of Daphnia to increase the NH₄:PO₄ ratio, whereas excretion from zebra mussels resulted in a decrease in both the N:P ratio (ranging from 9 to 13) and the NH₄:PO₄ ratio in water. In both treatments containing zebra mussels, P-rich water enabled sudden growth of Chlorophyta, resulting in blooms of Hydrodictyon reticulatum after 3–4 weeks of the experiment. Such phenomena were not observed in the control and Daphnia treatments. Our results indicate that zebra mussels, in contrast to Daphnia, may increase the symptoms of water eutrophication and contribute to blooms of expansive phytoplankton species.