Defining salinity limits on the survival and growth of benthic insects for the conservation management of saline Walker Lake, Nevada, USA

Walker Lake, Nevada, a saline desert lake, has been undergoing loss of stream inflows, lowering of lake level, and concentration of dissolved salts for over a century due to agricultural diversions of water. This lake is or has been inhabited by native fish and visited by many species of waterbirds that depend on productive invertebrate life for food resources. The extent to which salinity limits the present and future viability of resident invertebrate fauna was evaluated using salt-tolerance bioassays and studies of salinity effects on growth and behavior in larval stages of the midges Cricotopus ornatus and Tanypus grodhausi, and nymphs of the damselfly Enallagma clausum. We found that salinities into and above a range of 20–25 g/L present either lethal limits or sublethal inhibitions to survival and growth that will eliminate or substantially reduce the current community of common benthic invertebrates. All species survived best at salinities below the current ambient level, suggesting these populations are already under stress. The 72-h LC-50 for Cricotopus was 25 g/L, and while mature damselfly nymphs were somewhat more tolerant, early instars survived for only short times in increased salinity. Damselflies also grew more slowly and fed less when salinity increased from 20 to 30 g/L. A conservation level for the lake that incorporates survival of native fish and recovers diversity and viability of invertebrate life should be within the range of 10–15 g/L salinity of Walker Lake water.     

Macrozoobenthos in saline rivers in the Lake Elton basin: Spatial and temporal dynamics

The data on seasonal and interannual changes in the taxonomic, structural, and quantitative characteristics of macrozoobenthos communities in rivers with a high salinity gradient are given. A total of 91 benthic invertebrate taxa have been revealed, which were dominated by Cricotopus salinophilus, Chironomus salinarius, C. aprilinus, Tanytarsus kharaensis, Microchironomus deribae, Glyptotendipes salinus (Diptera: Chironomidae), Culicoides (M.) riethi, Palpomyia schmidti (Diptera: Ceratopogonidae), Paranais simplex (Oligochaeta), and Ephydra sp. (Ephydridae) in different years. The fauna of benthic communities is mainly represented by eurybiontic halotolerant species with different ranges of resistance to salinity. The taxonomic composition and diversity of macrozoobenthos communities are closely correlated with water salinity in the range from 4 to 41 g/L; the complex of hydrological and hydrophysical factors (depth, overgrowing, water temperature, pH, etc.) control the distribution and abundance of species.     

Ecological description of the sodium chloride mineral springs in the Kirenga River basin and the upper reaches of the Lena River: 1. General characteristics of the springs and their hydrofauna

The aquatic microecosystems and their environment have been studied in 12 mineral springs located in the Cis-Baikal Depression and in the basin of the upper reaches of the Lena River (Eastern Siberia). The hydrochemical characteristics of the springs, originating from the Cambrian salt deposits, are given. Their total mineralization varies from 1.1 to 123.0 g/L and the water is sodium chloride. The soils formed under the influence of the mineral waters (“para-soils”) are described. The data on the composition and quantitative abundance of aquatic fauna are presented. Six types of macroinvertebrate communities are described. The communities where Turbellaria, Gastropoda, and Psychodidae dominate are recorded in weakly mineralized waters (<3 g/L). The communities where Chironomidae dominate are found in waters characterized both by low and high (up to 28 g/L) salinity. In springs with a water salinity of 2.5–11 g/L, communities characterized by the dominance and high biomass of amphipods Gammarus lacustris Sars. are formed. A unique type of community where Ephydridae larvae dominate (>97% of the biomass) is described for the concentrated brines in Ust’-Kutskii spring. Halophilic species of crustaceans are recorded in the meiofauna. The presence of Foraminifera (marine organisms) in the two studied springs attracts specific interest.     

红树林植被对大型底栖动物群落的影响

大型底栖动物是红树林生态系统的重要组成部分,从红树林大型底栖动物种类、红树林与其周边生境大型底栖动物群落的比较,以及生境变化对动物群落的影响等方面阐述了红树林植被与大型底栖动物群落的关系.从物种数量上看,软体动物和甲壳类动物构成了红树林大型底栖动物的主要部分.影响大型底栖动物分布的环境因素包括海水盐度、潮位和土壤特性等,但在小范围区域,林内动物的分布更多地与红树林植被特性和潮位有关.因此,由于红树林植被破坏或者恢复引起的生境变化,将导致大型底栖动物群落和常见物种种群的变化,尤其对底上动物影响明显;随着人工恢复红树林的发育,林内底栖动物的多样性相应增加,优势种也发生变化.相比位于相同潮位的无植被滩涂,红树林可促进潮间带生物多样性.     

New data about deep-water solitary ahermatypic scleractinians of the shelf of Vietnam

This paper reports data on deep-water solitary ahermatypic corals that were collected on the shelf of Vietnam. Among these, 28 species belonging to 16 genera and eight families were identified; 9 species are first records for the South China Sea, and 2 species (Deltocyathus radiatus sp. n. and Flabellum septodentatus sp. n.) are described as new to science. Dendrophyllia sp. (33 indiv. in sample) and Truncatoflabellum crassum (28 indiv. in sample) formed massive aggregations. The taxonomically richest genera were Flabellum, Truncatoflabellum, and Caryophyllia. Coral density and species diversity were highest at depths of 90–230 and 285–390 m, respectively. Deep-water corals of Vietnam are integral with the coral fauna of the Indo-Polynesian Province. The data we obtained contribute to the knowledge of the composition and chorology of the worldwide fauna of solitary corals.     

Seed germination for an annual form of Zostera marina from the sea of Cortez,Mexico

Seed of Zostera marina L. collected at Punta Chueca, Sonora, that was germinated in artificial seawater under growth chamber conditions was less affected by salinity than by temperature. Mean germination was higher for seed collected on reproductive shoots in situ (43%) than for seed collected in fresh beach debris (17%), but no germination was recorded for seed collected in dried beach debris. Mean germination for seed kept at either 15 or 35‰ salinity was approximately equal. Earliest germination was recorded in late April 1980, two weeks after collection, and germination continued through March 1981 at 18–20°C, conditions which are comparable to winter water temperatures in Canal del Infiernillo. Germination was inhibited at 28–32°C, temperatures that are near summer water conditions. The germination responses reflect the adaptive strategies of an annual population to habitat conditions near the southern limit of the species.     

Ecophysiology of the estuarine cyanobacterium Lyngbya aestuarii to varying salinity in vitro

Lyngbya aestuarii, one of the dominant cyanobacterium grows in different salinity gradients of Chilika lagoon. It was isolated in axenic culture and its ecophysiology with response to different concentrations of salinity was studied in vitro to understand its adaptation strategies in the changing salinities of the lagoon. Changes in morphological features of the organism were observed with salinity gradients higher than 28 g/L and lower than 14 g/L salinity. Increase in growth was accompanied by increase of chlorophyll-a, carotenoid and cell protein contents of the organism from 3.5 to 28 g/L. Cellular carbohydrate content was higher with increasing salinity of the medium up to 90 g/L. No detrimental effect on pigment synthesis and macromolecular content of the organism was observed at the salinity level ranging from 7 to 56 g/L salinity. Methanolic extract of L. aestuarii showed prominent absorption at 334 nm in the UV-B region of the spectrum due to mycosporine-like amino acid (MAA) and the quantity of MAA increased with increasing salinity. At 7 g/L salinity 150, 93, 58, 34 and 18 kDa proteins were up-regulated; however, at 14 g/L 37, 26 and 28 kDa proteins and in 0, 3.5 and 90 g/L 122, 32 and 20 kDa proteins were repressed; this shows similarities of salinity-induced protein modifications as observed in higher plants. Super oxide dismutase activity also increased in the cells grown at 56 g/L salinity. We conclude because of having these effective adaptation strategies, L. aestuarii cope very well with the changing salinity in different seasons and grows well in the different sectors of the lagoon.     

Optimization of cultivation conditions for fatty acid composition and EPA production in the eustigmatophycean microalga Trachydiscus minutus

We determined the effects of cultivation conditions (nitrogen source, salinity, light intensity, temperature) on the composition of polyunsaturated fatty acids (PUFAs) and the production of eicosapentaenoic acid (EPA) in the laboratory cultured eustigmatophycean microalga, Trachydiscus minutus. T. minutus was capable of utilizing all nitrogen compounds tested (potassium nitrate, urea, ammonium nitrate, ammonium carbonate) with no differences in growth and only minor differences in fatty acid (FA) compositions. Ammonium carbonate was the least appropriate for lipid content and EPA production, while urea was as suitable as nitrates. Salinity (0.2 % NaCl) slightly stimulated EPA content and inhibited growth. Increasing salinity had a marked inhibitory effect on growth and PUFA composition; salinity at or above 0.8 % NaCl was lethal. Both light intensity and temperature had a distinct effect on growth and FA composition. The microalga grew best at light intensities of 470–1,070 μmol photons m^?2 s^?1 compared to 100 μmol photons m^?2 s^?1, and at 28 °C; sub-optimal temperatures (20, 33 °C) strongly inhibited growth. Saturated fatty acids increased with light intensity and temperature, whereas the reverse trend was found for PUFAs. Although the highest level of EPA (as a proportion of total FAs) was achieved at a light intensity of 100 μmol photons m^?2 s^?1 (51.1?± 2.8 %) and a temperature of 20 °C (50.9?±?0.8 %), the highest EPA productivity of about 30 mg L^?1?day^?1 was found in microalgae grown at higher light intensities, at 28 °C. Overall, for overproduction of EPA in microalgae, we propose that outdoor cultivation be used under conditions of a temperate climatic zone in summer, using urea as a nitrogen source.     

Selective feeding by baltic herring

Lake Lenore is a highly productive alkaline lake in the Lower Grand Coulee, Central Washington. Leakage of freshwater from nearby irrigation projects decreased the lake salinity from about 17 to 1.5 g/l during 1950–75. The initial bottom fauna with mass occurrence of single halobiontic chironomid species was supplanted by more diverse communities at all depths. The species richness increased by 2–8 times. The greatest addition of new species was found in the salinity range of 2–3 g/l. Concurrent increases in abundance and biomass suggest that the carrying capacity of the lake at higher salinities was not fully utilized by the benthos. A comparison with other eutrophic saline lakes indicates that benthic species composition and quantity is correlated with total salinity and ion composition.     

Seasonal and interannual variation of ichthyoplankton off the coast of the Moroccan Sahara

Changes in the qualitative and quantitative composition of ichthyoplankton off the coast of the Moroccan Sahara (21–28° N) in different seasons of 1994–2007 are analyzed. In this region, the pelagic eggs and larvae of over 100 fish species belonging to 62 families have been recorded. In cold periods, off the coast of the Moroccan Sahara there is peak in the spawning of fish of the subtropical fauna. The majority of them are European pilchard Sardina pilchardus, common scad Trachurus trachurus, and Atlantic mackerel Scomber japonicus. In warm periods there is intensive spawning of fish of the tropical fauna. Among them, dominants are round sardinella Sardinella aurita, West-African scad Trachurus trecae, and Atlantic bonito Sarda sarda. The spawning biomass of principal commercial fish is calculated by the quantity of eggs laid by females. The environmental factors are indicated that influence the fluctuation of abundance and distribution of ichthyoplankton in the region under consideration.     

Temperature and salinity tolerances of larval Californian grunion, Leuresthes tenuis (Ayres): A comparison with gulf grunion, L. Sardina (Jenkins & Evermann)

Temperature and salinity tolerances were determined for larval California grunion, Leuresthes tenuis (Ayres), and compared with previous data for Gulf of California grunion, L. sardina (Jenkins & Evermann). Larvae of similar age and acclimation history showed little interspecific difference in thermal tolerance, as measured by half-hour LT₅₀ values for 20–30 day old late postlarvae acclimated at various temperatures, and by upper and lower incipient lethal temperatures for 18°C-acclimated prolarvae. The upper incipient lethal temperature differed by 1 deg.-C (32°C for L. tenuis, 31°C for L. sardina), while the lower incipient lethal temperature for the 18°C acclimated prolarvae of both species was 7.5°C. L. tenuis larvae were much less euryhaline than L. sardina, with incipient lethal salinities of 4.2–41 %. for prolarvae and 8.6–38 %. for 20-day-old postlarvae; comparable values for L. sardina are 4–67.5 %. and 5–57.5 %. Both species show a decrease in temperature and salinity tolerance with age. The larvae of these disjunct congeners show a significant physiological divergence in euryhalinity but not in overall temperature tolerance. These tolerances are discussed in relation to the respective geographic ranges and behavioral responses of the two species.     

Photosynthetic and respiratory responses of Gracilaria parvispora from the southeastern Gulf of California

Photosynthetic and respiratory responses (P–E curves) of Gracilaria parvispora from the southeast Gulf of California were studied at four temperatures (20, 25, 30, 35 °C) and salinity (25, 30, 35, 40 psu) combinations. The alga showed acclimation in its photosynthetic and respiratory responses to tropical temperature as well as to oceanic salinity. A positive effect of temperature on photosynthetic rate (P _max) was observed for all salinities. Photosynthetic rates for treatments at 20 and 25 °C were lower (<9.2 mg O₂?g dry weight (dw)^?1?h^?1) than for treatments at 30 and 35 °C (>12 mg O₂ g dw^?1?h^?1). G. parvispora showed limited tolerance to low salinities (25 psu) and low temperatures (20 °C) and the interaction between temperature and salinity was significant (analysis of variance, P?<?0.05). Responses to salinity indicated adaptation to oceanic salinity. Photosynthetic responses were lower at 25 psu than at higher salinities. The lowest P _max values (6.2–8.2 mg O₂?g dw^?1?h^?1) were observed at the lowest salinity (25 psu) regardless of temperature. Compensation and saturation irradiances (26–170 and 57–149 μmol photons m^?2?s^?1, respectively) indicate adaptation to lower irradiances in shallow (1–2 m depth) habitats, where turbidity can be high, and the capacity of shade adaptation has been developed. Results suggest distribution of this species is mainly related to salinity or temperature. The potential mariculture efforts of G. parvispora would be limited by low temperatures in winter, and indicate that this species will probably not be able to spread further due to low temperatures (<15 °C) in the upper part of the Gulf of California.     

Distribution of diatom species on an estuarine mud flat and experimental analysis of the selective effect of stress

The distribution patterns of seven dominant diatom species on an estuarine mud flat transect were related to salinity gradients and organic pollution. The temporal distribution of species can be explained partly by the seasonal variation in irradiance and temperature, and partly by the large discharges of organically polluted fresh water during the late autumn. The selective effects of stress factors, such as low or high salinity, high concentrations of ammonia and free sulphide, and high temperatures were studied by measuring: (1) the tolerance of natural diatom populations isolated from the sediment; (2) the tolerance and capacities of unialgal cultures: and (3) the effects of the stress factors on the species composition of the populations in sediment samples incubated in the laboratory. A low salinity (1‰), but not a high salinity (20‰), markedly altered the species composition of natural diatom populations kept in the laboratory. Navicula salinarum Grunow and N. cf. cryptocephala Kützing outcompete other species only at a salinity of 1‰, which is below the optimum salinity for growth of these species. High concentrations (2–4 mM) of ammonia inhibited the photosynthesis of N. phyllepta Kützing and N. flanatica Grunow and decreased the cell numbers of these species in mixed populations kept in the laboratory. N. salinarum and Gyrosigma fasciola (Ehr) Cleve were relatively ammonia-tolerant and reached their highest abundance during periods of large discharges of organically polluted water. The populations on the mud-flat stations that had black, sulphide-containing layers 1 mm below the surface of the sediment, were dominated by the relatively sulphide-tolerant Navicula salinarum and N. pygmaea Kützing.High values of irradiance and temperature were a selective factor explaining the absence of N. flanatica in summer. Uptake of organic substrates and the inhibitory effect of high population densities are discussed in regard to their possible modifying influence on the distribution of diatom species on the mud flat.     

Seed germination ecology of the annual grass Leptochloa panicea ssp. mucronata and a comparison with L. panicoides and L. fusca

Leptochloa panicea ssp. mucronata is an annual grass that grows in relatively dry habitats. Requirements for dormancy loss and germination were determined for seeds of this species and compared to those of two species from wet habitats. Seeds of L. panicea were dormant at maturity in autumn, but when exposed to actual or simulated autumn temperatures (e.g. 20/10, 15/6 °C), they entered conditional dormancy and thus germinated to high percentages in light at 35/20 °C. Seeds buried in non-flooded soil exposed to natural seasonal temperature changes in Kentucky (USA) were non-dormant by the following summer and germinated to 80–100 % in light at 25/15, 30/15 and 35/20 °C. Seeds buried in non-flooded soil exhibited an annual conditional dormancy/non-dormancy cycle, with seeds mostly germinating to 80–100 % in light at 30/15 and 35/20 °C throughout the year but to 80–100 % in light at 25/15 °C only in summer. Results for L. panicea were compared to published data for L. panicoides and L. fusca. Whereas seeds of L. panicea buried in flooded soil failed to come out of dormancy, those of L. panicoides, an annual of moist habitats such as mudflats, exhibited an annual conditional dormancy/non-dormancy cycle, and those of L. fusca, a semi-aquatic, required flooding for both dormancy loss and germination. Differences in dormancy breaking and germination responses of seeds of Leptochloa species may help to explain why this genus occupies a wide range of habitats with regard to soil moisture conditions.     

Transition from Planktonic to Benthic Algal Dominance Along a Salinity Gradient

Highly regulated salinity gradients in solar salt pond concentrating sequences provide an opportunity to investigate in situ salinity impacts on aquatic flora and fauna. The Shark Bay Salt solar ponds at Useless Inlet in Western Australia vary in salinity from seawater to four times seawater over the pond sequence. We observed a shift from planktonic to benthic primary productivity as salinity increased. Water column photosynthesis and biomass decreased markedly with increasing salinity, while benthic productivity increased as cyanobacterial mats developed. Correspondingly, productivity shifted from autotrophy to heterotrophy in the water column and from heterotrophy to autotrophy in the benthos. Both shifts occurred at intermediate salinity (S = 110 g kg⁻¹, ρ = 1.087 g cm⁻³) in the pond sequence, where there was little production by either. Within individual ponds, productivity, algal biomass and physico-chemical conditions were relatively constant over one year, with only water column photosynthesis significantly different between seasons, mostly due to greater winter production. Transitions between benthic and planktonic production and their relative magnitudes appear to be driven mostly by direct responses to salinity stress, but also by changes in nutrient availability and grazing, which are also influenced by salinity.     

Salinity as a determinant of salt lake fauna: a question of scale

High and often variable salinity is an obvious feature of salt lakes. Correspondingly, salinity is usually assumed to be an important ecological determinant in such lakes. An investigation of the macroinvertebrate fauna of 79 lakes (salinities from 0.3 to 343 g 1^–1) in the Western District of Victoria, Australia, examined this assumption. Over the total range of salinity, species richness and composition are highly correlated with salinity. However, these relationships become nonsignificant over intermediate ranges of salinity. Furthermore, many taxa have very broad tolerances to salinity at these intermediate ranges, implying that factors other than salinity may determine their distribution. An appreciation of scale (that is, the range of salinity over which observations are considered) resolves the paradox that, despite these broad tolerances by most taxa, species richness and composition strongly reflect salinity over the entire salinity range.     

Mixed populations of marine microalgae in continuous culture: Factors affecting species dominance and biomass productivity

Marine microalgae were grown in multispecies continuous cultures. Under carbon dioxide limitation, blue-green algae dominated. Under nitrate and light limitation, species dominance depended on the initial conditions. When the inoculum consisted primarily of blue-green algae with smaller amounts of other species, blue-green algae and pennate diatoms dominated. When the inoculum consisted of equal amounts of all species, green flagellates and pennate diatoms dominated. Green flagellates and blue-green algae were incompatible and never shared dominance. When nutrient limitations were overcome, the productivity of seawater was increased 100-fold before light limitation occurred. The productivity could be further increased by reducing photorespiration in the culture. The dilution rates studied (0.1, 0.2, and 0.4 day(-1)) had no effect on species dominance, nor did the higher dilution rates select for smaller cells. The maximum productivity occurred at a dilution rate of 0.2 day(-1). Temperature had the greatest effect on species dominance, with green flagellates, pennate diatoms, and blue-green algae dominating at 20 degrees C and only blue-green algae dominating at 35 degrees C. The productivity at 35 degrees C was lower than that at 20 degrees C because of the lower solubility of carbon dioxide at higher temperatures. At 10% salinity, green flagellates and pennate diatoms dominated. The productivity at this salinity was 50% that obtained at the salinity of seawater (3.5%). At 25% salinity, only the green flagellate, Dunaliella salina, survived at a productivity of 1% that obtained at the salinity of seawater.     

New paleoenvironmental insights on the Miocene condensed phosphatic layer of Salento (southern Italy) unlocked by the coral-mollusc fossil archive

From the Late Oligocene to the Late Miocene, the central Mediterranean area was characterized by the extensive deposition of phosphate-rich sediments. They are usually represented by 10 to 20-cm-thick hardgrounds made of phosphatic and glauconitic sediments containing a rich macrofossil association. This study represents the first thorough investigation of the biotic assemblage of Mediterranean phosphorites aimed at collecting new information on the environmental factors controlling their deposition. The Serravallian/Tortonian phosphatic deposits of the Salento Peninsula (“Aturia level”) have been selected for the abundance of fossil remains and special attention is given to the coral–mollusc association. Two different facies have been recognized: a basal coral rudstone that includes most of the macrofossils, superimposed by a detrital rudstone made of thin layers mainly composed of phosphatic fragments. These two facies are separated by a phosphatic crust several millimeters in thickness. The coral assemblage contains at least 17 azooxanthellate taxa belonging to four families, while the molluscs are represented by a rich gastropod fauna (26 species), associated with bivalves (18 species) and cephalopods (two species). Four distinct depositional phases have been recognized, with the coral rudstone representing the key-facies to reconstruct the onset of the “Aturia level” and the original environment of its fossil content. The composition of the coral–mollusc association has been reliably compared with present-day analog taxa, suggesting the occurrence of a heterogeneous seafloor formed by rocky substrates and accumulations of soft sediment, at around 100–350-m water depth, and under the influence of moderate-to-strong bottom currents rich in nutrients and resuspended organic matter.     

Prokaryotic Community Structure Driven by Salinity and Ionic Concentrations in Plateau Lakes of the Tibetan Plateau

The prokaryotic community composition and diversity and the distribution patterns at various taxonomic levels across gradients of salinity and physiochemical properties in the surface waters of seven plateau lakes in the Qaidam Basin, Tibetan Plateau, were evaluated using Illumina MiSeq sequencing. These lakes included Lakes Keluke (salinity, <1 g/liter), Qing (salinity, 5.5 to 6.6 g/liter), Tuosu (salinity, 24 to 35 g/liter), Dasugan (salinity, 30 to 33 g/liter), Gahai (salinity, 92 to 96 g/liter), Xiaochaidan (salinity, 94 to 99 g/liter), and Gasikule (salinity, 317 to 344 g/liter). The communities were dominated by Bacteria in lakes with salinities of <100 g/liter and by Archaea in Lake Gasikule. The clades At12OctB3 and Salinibacter, previously reported only in hypersaline environments, were found in a hyposaline lake (salinity, 5.5 to 6.6 g/liter) at an abundance of ∼1.0%, indicating their ecological plasticity. Salinity and the concentrations of the chemical ions whose concentrations covary with salinity (Mg²⁺, K⁺, Cl⁻, Na⁺, SO₄²⁻, and Ca²⁺) were found to be the primary environmental factors that directly or indirectly determined the composition and diversity at the level of individual clades as well as entire prokaryotic communities. The distribution patterns of two phyla, five classes, five orders, five families, and three genera were well predicted by salinity. The variation of the prokaryotic community structure also significantly correlated with the dissolved oxygen concentration, pH, the total nitrogen concentration, and the PO₄³⁻ concentration. Such correlations varied depending on the taxonomic level, demonstrating the importance of comprehensive correlation analyses at various taxonomic levels in evaluating the effects of environmental variable factors on prokaryotic community structures. Our findings clarify the distribution patterns of the prokaryotic community composition in plateau lakes at the levels of individual clades as well as whole communities along gradients of salinity and ionic concentrations.     

Qualitative study of Mollusca communities in the Serbian Danube stretch (river km 1260–863.4)

First detailed limnological study was performed from April 2003 to June 2008 in a 396.6 km long section of the Serbian Danube (divided in three parts; from 1260 r-km to 863.4 r-km) to examine community composition and spatial distribution of Mollusca with special attention to the expansion of Ponto-Caspian species, propagation of invasive and introduced species and occurrence of endemic species. Mollusca samples were collected at 15 sites in April, June, September and November. We investigated the spatial distributions and calculated the faunistic similarity of localities with respect to the community composition using the Sørensen Quotient of Similarity. Site variation in analyzed qualitative traits was examined using correspondence analysis. Additionally, the obtained Complete Linkage City-block (Manhattan) distances among sites/parts were subjected to UPGMA (unweighted pair-group method using arithmetic averages) cluster analysis. The class Gastropoda was represented by 18 species from two subclasses (Prosobranchia — six families and Pulmonata — three families).The class Bivalvia was represented by 15 species from four families of order Eulamellibranchiata. Mollusca were represented by 33 species belonging to 17 genera and 13 families. Out of five recorded Ponto-Caspian species in the studied Danube stretch, Lithoglyphus naticoides (Pfeiffer, 1828) and Dreissena polymorpha (Pallas, 1771) are assumed to be invasive species with the highest occurrence frequency (F = 1, each). Four new species in invertebrate fauna for the Danube, denoted as the introduced species — Neozoa, were identified: Theodoxus fluviatilis (L., 1758), Corbicula fluminalis (Müller, 1774), C. fluminea (Müller, 1774), and Sinanodonta woodiana (Lea, 1834). The only endemic species of Gastropoda found in the Danube was Viviparus acerosus Bourguignat, 1862.