Snail Assemblages Research Articles

What do Lateglacial and Holocene land snail communities tell us about the palaeoenvironments of Mediterranean France?

Southeastern France occupies a key biogeographical position on the lower Rhone corridor, at the interface between southern and northern Europe. It is also at the heart of long‐standing ecological debates about the respective roles of natural and human drivers in shaping the Mediterranean landscape. Molluscan analysis may represent a valuable contribution to this issue. In this paper, land snail assemblages from three calcareous tufa deposits in the Luberon mountain were used to reconstruct Lateglacial and Holocene palaeoenvironments. The Lateglacial communities only differ from the Pleniglacial ones by the development of hygrophilic snails. We note a high moisture budget at the end of the Lateglacial Interstadial (LGI). A patchy, steppe landscape is attested. A time lag in recolonization by woodland species during the LGI is conceivable. The postglacial woodland assemblages then trace a laborious reassembly of forest snail communities. It takes place mainly between c. 8000 and c. 6600 cal. a BP with spatial disparities and delayed recruitments. The French Mediterranean region has not benefitted from the macrorefugia that it would have sheltered or with which it would have been close. Woodlands, however, appear progressively more closed and complex c. 8000 cal. a BP. They reached their optimum c. 7500 to 7400 cal. a BP although their canopy seems to have stayed quite open. Anthropization remained weak during the Early Neolithic. A significant woodland opening is observed in the Early–Middle Neolithic. Human impact becomes clear from the Late Neolithic. Nevertheless, there are substantial differences compared with Basse‐Provence, where a more marked openness of the landscape from 7000 cal. a BP was accompanied by the development of Mediterranean synanthropic snails. The molluscan successions of the Luberon mountain should be a reference for the development of the Lateglacial and Holocene malacofauna in the SE of France, at the northern boundary of the western Mediterranean domain.

Not Blown away: Over Three-Quarters of Species in a Pacific Atoll Land Snail Assemblage Remain Five Years Post-Typhoon

Not Blown away: Over Three-Quarters of Species in a Pacific Atoll Land Snail Assemblage Remain Five Years Post-Typhoon

Not Blown away: Over Three-Quarters of Species in a Pacific Atoll Land Snail Assemblage Remain Five Years Post-Typhoon

Not Blown away: Over Three-Quarters of Species in a Pacific Atoll Land Snail Assemblage Remain Five Years Post-Typhoon

Land snail assemblages along altitudinal gradients on Mount Semeru, the highest montane forest in Java, Indonesia

ABSTRACT We conducted research on land snail diversity on the highest volcanic mountain in Java, Mt Semeru. This research aimed to gain data on the land snail species diversity in the area as well as analyse environmental variables that affect the land snail assemblages along the altitudinal gradients. A total of 40 plots of 10 × 10 m2 were examined in the altitudinal gradient of 800–1,200, 1,201–1,600, 1,601–2,000 and 2,001–2,400 m asl using a timed search method. In total, 788 individuals of land snails were collected, belonging to 22 species from 14 families. Fifteen species were new records for the area. Five endemic species were recorded on Mt Semeru. A single introduced species, Bradybaena similaris was found abundantly on the mountain at an altitude of more than 2,000 m asl. Multiple linear regression analyses showed a unimodal response of species richness for altitude, temperature and precipitation sums on Mt Semeru. In addition to these environmental variables, species richness is influenced by land use type and soil pH. These findings suggest that species and ecosystem management at the altitude 2,001–2,400 m asl is necessary to conserve endemic land snail species, which were found most abundantly at this altitude.

A native species contributes to biotic homogeneity of urban land snails in Thailand

ABSTRACT Biotic homogenization or the increasing similarity of biota has been documented in urban land snail assemblages in Europe and North America. The resulting biotic homogeneity is caused by a loss of native species and the establishment of non-native species. Climate affects land snail distributions, and because Thailand (exclusive of the southern peninsula) has an almost uniform climate, we hypothesized that urban land snail populations would show a high degree of taxonomic homogeneity. We sampled 76 sites (e.g. yards, temple grounds, restaurants and hotels) over a 38-day period during the rainy season in 2022. These sites included three regions: central (five provinces), north (two provinces) and northeast (five provinces). Both live snails and shells were counted, and the 10,470 counted individuals represented 25 taxa. Biotic homogeneity was indicated by three taxa comprising 69.9% of individuals. By far the most abundant species was the native species Sarika siamensis, which was found at all 76 sites and comprised 50.4% of all individuals. The other two abundant species were non-native species—the giant African snail Lissachatina fulica (60 sites) and Allopeas gracile (50 sites)—both widespread synanthropic species. Three other non-native species were also found. Among native species, slugs, including semislugs, were widespread but occurred in low numbers, and Pupina sp. occurred in high abundance (mean = 97 individuals/site) at 13 highly watered locations within its native range. Urban snail assemblages were not entirely homogeneous, as assemblages in the north region differed from those in the central and northeast regions. In conclusion, urban snail assemblages in Thailand showed a high degree of biotic homogeneity, in large part due to a native species, S. siamensis, indicating that native synanthropic species can contribute to biotic homogeneity.

Gastropod assemblages in the harsh environment of Mediterranean Dinaric karst intermittent rivers

Freshwater snails inhabit a wide range of freshwater habitats, including the intermittent ones, specific adaptations enabling them to survive the dry phase for an extended period of time. Despite an increasing scientific interest in biota occurring in intermittent freshwater habitats, our knowledge about environmental factors shaping freshwater gastropod assemblages in such habitats is still poor. Therefore, this study aimed to assess gastropod assemblage composition in four karst intermittent rivers in the Mediterranean during the lotic phase, compare gastropod taxa richness and abundance among the rivers, and determine their relationships with environmental variables. A total of six taxa was recorded, with each river harbouring a unique, species-poor (up to three species) assemblage. Gastropod assemblages were influenced by the physico-chemical water properties, especially the concentration of dissolved oxygen in water, conductivity, and chemical oxygen demand. Our results provide a basis for further research on freshwater snail assemblages in the Mediterranean karst intermittent rivers, as the need to protect these vulnerable ecosystems and develop adequate monitoring practices becomes imperative due to climate change and anthropogenic pressures.

The type of forest edge shapes snail assemblages at forest–pasture transitions

Semi-natural, nutrient-poor calcareous grasslands are local biodiversity hotspots that are increasingly threatened by land use intensification, abandonment, or indirect effects from adjacent habitats. The habitat quality of these grasslands is often influenced by neighbouring forests or intensively managed agricultural land. For example, shrubs encroaching on grassland reduce the sensitive habitat, but at the same time represent a new habitat type (transition zone at gradual forest edge). We investigated the effects of gradual and abrupt forest edges on the species richness, abundance, species composition, functional diversity and number of species of conservation importance (red-listed species) of land snail assemblages at forest–pasture transitions in the Jura Mountains, Switzerland. Forest edge type influenced the snail assemblages in different ways. Transition zones at abrupt forest edges had a higher species richness and more snail individuals than transition zones at gradual forest edges. Transition zones also differed in land snail species composition. At gradual forest edges, the transition zones contained some openland snail species, while those at abrupt forest edges had a similar species composition to the forest interior. Functional diversity was significantly higher for snails in the forests and transition zones at both abrupt and gradual edges than in pastures. In contrast, pastures and transition zones at both abrupt and gradual edges had a significantly higher number of red-listed snail species. Based on our findings, we recommend the creation of gradual forest edges through regular forest management practices, rather than through shrub encroachment into pasture, which could reduce the size of the threatened habitat.

Hydrological connectivity shapes multiple diversity facets of snail (Mollusca: Gastropoda) assemblages in freshwater floodplain wetlands

Hydrological connectivity is crucial for supporting aquatic biodiversity and serving ecosystem function in river floodplain wetlands. Although the effects of longitudinal connectivity in the composition of snail (Mollusca: Gastropoda) assemblages is well understood, the effects of lateral connectivity are less evaluated. Here, we evaluated the effects of lateral and longitudinal connectivity on multiple facets of alpha and beta diversity (i.e., taxonomic, functional, and phylogenetic) of freshwater snails in 38 floodplain wetlands in the Da Xing'an Mountains of Northeast China. A total of 9,784 snails subjected to 5 orders, 14 families, 24 genera, and 42 species were collected. Overall, the snail alpha diversity was higher in the nearly isolated wetlands and downstream areas. Multivariate analyses revealed that the taxonomic, functional, and phylogenetic structures of snail assemblages in floodplain wetlands differed significantly across the lateral and longitudinal gradients. Waterscape and climate variables appeared to equivalently explain a large proportion of variations in the taxonomic, functional, and phylogenetic structures of snail assemblages. Lateral connectivity and river order were paramount variables that explain the greatest variation in taxonomic, functional, and phylogenetic structures of the snail assemblages. Our study suggests that hydrological connectivity is a key factor controlling the multiple facets of snail diversity in floodplains. Attention should be paid to the effects of changing climate and waterscape on the multi-faceted diversity of snail assemblages. Due to the extant patterns in assemblage structures, floodplain restoration and management should consider the full spectrum of longitudinal and laterally connectedness to maximize aquatic biodiversity.

Geographical and climate‐dependent patterns in spatial distributions of snail (Mollusca: Gastropoda) assemblages in freshwater wetlands across Northeast China

Abstract A central goal of community ecology and biogeography involves understanding the spatial patterns of organisms and their underlying mechanisms. Understanding how the structure of wetland biomes vary throughout geographical or climatic gradients has critical implications for the ecological restoration and management of wetlands. However, the geographical patterns of snails in freshwater wetlands and the relative contributions of climatic and local environment variables remain poorly elucidated. We investigated 126 freshwater wetlands across four ecoregions (Da Xing'an Mountains, Songnen Plain, Sanjiang Plain and Changbai Mountains) in Northeast China, and collected 105578 individual snails (Mollusca: Gastropoda) belonging to 17 families, 34 genera and 64 species. Overall, snail richness and functional alpha diversity was higher in the wetlands of the Sanjiang Plain than the other three regions. Multivariate analyses results revealed that the taxonomic, functional and phylogenetic structures of snail assemblages differed significantly across the four regions. Higher taxonomic dissimilarities, as well as functional and phylogenetic dissimilarities existed between the wetlands of the Songnen Plain and the other three regions. The variations in taxonomic, functional and phylogenetic structures of snail assemblages were predominantly explained by climatic variables rather than by local environmental variables. For taxonomic structure, salinity explained the greatest variation among all variables, whereas precipitation seasonality explained the greatest variation for functional and phylogenetic structure. Considering extant patterns in assemblage structure and its predictors, aggravated salinization and seasonality of precipitation are expected to act as powerful factors shaping future assemblages. Also, climate‐related factors cause changes and spatial distribution of invertebrate assemblages of freshwater wetlands should be considered to formulate differentiated strategy for biodiversity conservation.

Long-interval effects of wildfires on the functional diversity of land snails

In fire-prone regions, fire is a major natural disturbance which shapes ecosystem function and community composition. Fire has a direct and dramatic effect on soil fauna and, especially, on non-mobile species such as land snails. The factors that make the Mediterranean Basin a fire-prone region may also lead to the appearance after fires of certain functional traits related to ecological and physiological characteristics. Knowledge of how community structure and function change along the post-fire succession will be useful for understanding the processes that drive biodiversity patterns in burnt areas and for implementing appropriate biodiversity management strategies. Here, we examine long-interval taxonomic and functional changes occurred in a snail community four and 18 years after a fire in the Sant Llorenç del Munt i l'Obac Natural Park (NE Spain). Our field-based study demonstrates that the land snail assemblage responds both taxonomically and functionally to fire and that there was a clear replacement of dominant species from the first to the second sampling period. Variation in community composition between different post-fire ages can be attributed to snail species traits and successional changes in post-fire habitat conditions. At taxonomic level, there was great variation in snail species turnover between both periods, being the development of the understorey vegetation structure the main driver of this variation. The replacement of functional traits between times since fire suggests that xerophilic and mesophilic preferences play an important role after fire and are largely determined by the complexity of post-fire microhabitats. Our analysis indicates that immediately after a fire there is a time-window of opportunity that attracts species specializing in early successional habitats, which thereafter are replaced due to the changing conditions resulting from succession. Consequently, knowing the functional traits of species is important for determining the impacts of disturbances on the taxonomic and functional communities.

Trophic niche size and overlap in temperate forest land snails are affected by their lifestyle and body size

Abstract Land snails represent a large diversity of species in the forest floor. Some species prefer to stay in the leaf litter, while others like to climb up vegetation. They are considered generalist herbivores/decomposers. Although the exact trophic position of most species is often difficult to determine, a low rate of trophic niche partitioning within an assemblage is assumed. We compared isotopic niche sizes and overlaps between and within four local land snail assemblages using stable isotope Bayesian ellipses. We found significant differences in trophic niche size (expressed by corrected standard ellipse area) as a function of body size and lifestyle. We hypothesised that the larger niche size of smaller and/or arboreal snail species is due to their limited mobility and the presence of spatially structured food resources. In contrast, a broad and similar mixture of leaf litter sources results in a homogeneous diet for individuals of larger, highly mobile, epigean species, i.e., smaller niche size. We documented multiple overlaps of isotopic niches between species within an assemblage, although arboreal species exhibited slightly different niche positions, indicating specific diets. When comparing all pairwise combinations, we found that isotopic niches of species using different lifestyle did not overlap, in contrast to species using similar lifestyle. In addition, the trophic niches of opportunists with respect to lifestyle were intermediate between those of species from the outermost categories. Our results fit the general concept of variable and overlapping trophic niches in co-occurring snail species. However, we were able to demonstrate differences in species that rarely occupy the same microhabitat.

Macro Land Snail Diversity and Community Assemblage in Selected Forest Fragments of Leyte Island, Philippines

The diversity of land snails in Leyte Island has not been examined over the past few years. To address this, a survey of macro land snails (> 5 mm in shell height and diameter) in selected forest fragments of Leyte was conducted. A total of 120 quadrats (10 x 10 m) were set in three sampling sites (Inopacan, Baybay, and Maasin) that varies in area size – with Baybay being the largest fragment, followed by Inopacan and Maasin. From a total of 592 individuals, 22 macro land snail species and five families were identified. The macro land snail assemblage was dominated by endemic eupulmonates (Order Stylommatophora) and caenogastropods (Order Architaenioglossa). Among eupulmonates, Family Camaenidae had the most species (10), followed by Trochomorphidae and Achatinidae (two each), and Helicarionidae (one). For caenogastropods, all seven species were under Family Cyclophoridae. Cyclophorus appenidiculatus was the most abundant, representing 16.65% of the total number of individuals. Lissachatina fulica, an invasive land snail, was also documented in all sites. A β-dominated community assemblage was revealed by species accumulation curves with sampling efficiency using a completeness ratio of 1, which indicates a highly efficient sampling method. Detrended correspondence analysis indicated high similarity in species composition among study sites, with two unique species (Subulona cylindracea and Hypselostyla boholensis) recorded in Maasin and two incidental records (Obba bigonia and Helicobulinus sarcinosa). This study yielded 15 new records of macro land snail species during the sampling. There were five species (Hemiglypta semiglobosa, Amphidromus maculiferus, Leptopoma perlucidum, Chloritis leytensis, and Obba bigonia) that were documented on earlier records on the island, but 33 of the previously recorded macro land snail species were not encountered in the study. The community ecology patterns were also documented in the fragmented forests of Leyte, which is very important in local malacofaunal conservation and management.

Subtle Effects of Experimental Grassland Fragmentation on Density, Species Composition and Functional Dispersion of Gastropods

The fragmentation of continuous habitats has significant consequences for species and for the functional diversity of plant and animal communities. Fragmentation effects can be indirect, can occur at different spatial scales and may vary over years. Small fragmentation-related effects may only be detected in standardized, controlled field experiments accounting for the natural variation in environmental conditions and in remnants of habitat. Using a non-invasive trapping approach, we examined the responses of terrestrial gastropods (snails and slugs) to small-scale habitat fragmentation in a controlled experiment conducted in three species-rich, nutrient-poor calcareous grasslands in the Jura Mountains, Switzerland, over four years. We found site-specific differences in species richness, individual density, and species composition. Experimental grassland fragmentation did not significantly affect species richness or density, but affected functional dispersion (a measure of functional diversity) in the final year, indicating that fragmentation-related changes may occur with a time delay. Similarly, experimental fragmentation influenced the mean shell size of the snail assemblage and the proportions of individuals with certain life-history traits or habitat preferences in some years. The observed fragmentation effects were subtle and varied over time, underlining the importance of controlled field experiments.

Land snail assemblages and microhabitat preferences in the urban areas of Kolkata, India

AbstractDue to the minimal dispersal capabilities and dependency on particular microhabitat, the land snails are susceptible to anthropogenic and natural disturbances. Considering the increasing anthropogenic threats, especially in urban areas, information on species’ requirements for particular habitat is very essential for land snail conservation and sustenance. In the present commentary, diversity and distribution of small-sized land snails in relation to their microhabitat preference in urban habitats of Kolkata, West Bengal, had been carried out through the quadrat method. The information on the richness and abundance of snails and their habitat places in Kolkata, India, was used to construct a bipartite network. A total of 13 land snail species were linked with 16 microhabitats. The network indices were used to justify the specialist or generalist nature of the snail species in the context of microhabitat preference. The snail species Succinea daucina and Allopeas gracile were observed to be associated with the maximum number of habitats while species strength was highest for S. daucina. The low value of connectance (0.288, <0.5) and niche overlap (0.34), the high value of specialization index H2′ (0.58) and d′ (0.44) indicate that the snail–microhabitat interactions were highly specialized. The network ecology of snail–microhabitats illustrated in the present instance will enable the identification of preferred microhabitats, which are required for the enhancement of the population of land snails in urban areas like Kolkata, India.

Malaco temperature reconstructions and numerical simulation of environmental conditions in the southeastern Carpathian Basin during the Last Glacial Maximum

ABSTRACTWe investigate the glacial climate conditions in the southeastern Carpathian Basin (Vojvodina, Serbia) based on the reconstruction of malacological palaeotemperatures and results from a high‐resolution regional climate simulation. Land snail assemblages from eight loess profiles are used to reconstruct July temperatures during the Last Glacial Maximum (LGM). The malacological reconstructed temperatures are in good agreement with the simulated LGM July temperatures by the Weather Research and Forecast model. Both methods indicate increasing temperatures from the northwestern towards the southeastern parts of the study area. LGM aridity indices calculated based on the regional climate model data suggest more arid conditions in the southeastern parts compared with more humid conditions in the northwestern parts. However, for present‐day conditions, the moisture gradient is reversed, exhibiting more humid (arid) conditions in the southeast (northwest). An explanation for the reversed LGM aridity pattern is provided by an analysis of the prevailing wind directions over the South Banat district (Serbia). The prevailing moist northwesterly winds during summer are not able to compensate for the annual lack of moisture induced by the dry winds from the southeast that are more frequent during the LGM for the other seasons.

Ditches as important aquatic invertebrate habitats: a comparative analysis of their snail (Mollusca: Gastropoda) assemblages with natural wetlands

Wetlands and ditches are both common aquatic habitats in lowland landscapes of northeast China. However, most biodiversity management and research for aquatic organisms has focused on the biota of natural wetlands, and the invertebrate fauna of ditches has not been previously addressed. Because ditch habitats can be so extensive in some landscapes, their contribution could be substantial. To assess the contributions of ditches to invertebrate biodiversity, snail assemblages of natural wetlands, wetland ditches, and agricultural ditches in the Sanjiang Plain of northeastern China were compared. Snail assemblages of the three habitats all differed significantly from each other. Species richness and abundance of snail assemblages in wetland ditches was similar with natural wetlands. Although lower, species richness and abundance of snail assemblages in agricultural ditches still accounted for 22% and 52%, respcetively, of that in natural wetlands. Each of the three different habitats supported unique species, with 11 snail species being indicators of specific habitat types. Biota and Environment matching analysis (BEST) showed that pH in combination with dissolved oxygen were the most important environmental factors in explaining the dissimilarities of snail assemblages among the three different habitats. This study illustrates that both wetland ditches and agricultural ditches make contributions to aquatic invertebrate biodiversity in Sanjiang Plain. More attention should be paid to the importance of ditches as reservoirs for aquatic invertebrates, and the biota of ditches should be considered in the overall scope of biodiversity management and monitoring.

Narrow environmental niches predict land-use responses and vulnerability of land snail assemblages

BackgroundHow land use shapes biodiversity and functional trait composition of animal communities is an important question and frequently addressed. Land-use intensification is associated with changes in abiotic and biotic conditions including environmental homogenization and may act as an environmental filter to shape the composition of species communities. Here, we investigated the responses of land snail assemblages to land-use intensity and abiotic soil conditions (pH, soil moisture), and analyzed their trait composition (shell size, number of offspring, light preference, humidity preference, inundation tolerance, and drought resistance). We characterized the species’ responses to land use to identify ‘winners’ (species that were more common on sites with high land-use intensity than expected) or ‘losers’ of land-use intensity (more common on plots with low land-use intensity) and their niche breadth. As a proxy for the environmental ‘niche breadth’ of each snail species, based on the conditions of the sites in which it occurred, we defined a 5-dimensional niche hypervolume. We then tested whether land-use responses and niches contribute to the species’ potential vulnerability suggested by the Red List status.ResultsOur results confirmed that the trait composition of snail communities was significantly altered by land-use intensity and abiotic conditions in both forests and grasslands. While only 4% of the species that occurred in forests were significant losers of intensive forest management, the proportion of losers in grasslands was much higher (21%). However, the species’ response to land-use intensity and soil conditions was largely independent of specific traits and the species’ Red List status (vulnerability). Instead, vulnerability was only mirrored in the species’ rarity and its niche hypervolume: threatened species were characterized by low occurrence in forests and low occurrence and abundance in grasslands and by a narrow niche quantified by land-use components and abiotic factors.ConclusionLand use and environmental responses of land snails were poorly predicted by specific traits or the species’ vulnerability, suggesting that it is important to consider complementary risks and multiple niche dimensions.

Biotic homogenization or riparian refugia? Urban and wild land snail assemblages along a subtropical precipitation gradient

Abstract A noted impact of urbanization is the tendency for biotic homogenization, or the increase of similarity of geographically disparate communities. On the other hand, some urban habitats harbor biodiversity native to their region, a role potentially important in xeric landscapes, with irrigation increasing the coverage and availability of mesic habitats in an otherwise water-limited landscape. We assessed the relative importance of urban yards as agents of biotic homogenization or riparian refugia by characterizing community composition of Tamaulipan thornforest land snail assemblages across a pronounced precipitation gradient in far south Texas, USA. We quantified α- and β-diversity and assessed whether the land snail fauna of urban yards are more similar to each other across a precipitation gradient than they are to their wild counterparts, as well as determined the significance of moisture in driving Tamaulipan thornforest β-diversity, both in terms of turnover (changing species composition) and nestedness (species loss). Sites with both the wild and wet conditions had the highest values of species richness and abundance. Urban land snail communities were significantly homogenized, outweighing the influence of the precipitation gradient. We did not find urban yards served as a refuge for native, moisture-dependent, riparian snails. Our analyses find that turnover, not nestedness, is the largest contributor to β-diversity in these assemblages. Studies of urbanization should address regional spatial scales to quantify how urbanization modifies regional biodiversity arising from background environmental gradients. Such an approach could lead to improved understanding of how large metroplex areas could be used to maintain and even promote biodiversity.

Stable isotope analysis suggests low trophic niche partitioning among co‐occurring land snail species in a floodplain forest

AbstractLand snails are abundant invertebrates in many terrestrial ecosystems, playing an essential role in food webs and nutrient cycling. Although snails are commonly considered general grazers with a strong tendency to omnivory, their foraging strategy is well documented only for a few species. Virtually no data exist on trophic niche partitioning within snail assemblages. To fill this gap, we analyzed naturally occurring stable isotope (δ13C, δ15N), an approach widely applied in ecological research, but only rarely in terrestrial snail studies. We collected ten individuals of the dominant co‐occurring land snails (i.e., Aegopinella nitidula, Fruticicola fruticum, Oxyloma elegans, Succinea putris, Trochulus villosulus and Zonitoides nitidus) in a floodplain forest floor, along with their potential food sources and other invertebrates. All species, except for A. nitidula, showed high intraspecific variation in isotope signatures, indicating their opportunistic feeding behavior. Such a high intraspecific variation combined with the active movement range of all the species allows switching between food sources based on their accessibility. We observed that the trophic niches of the studied species highly overlapped, except for Z. nitidus. This suggests that trophic niche compartmentalization among co‐occurring species does not seem to be the mechanism to avoid competition for food. Virtually unlimited resources for snail food are assumed to explain the coexistence of many species in high‐density populations. Our results add to this concept of assembly rules in snail species by the finding of highly variable and overlapping trophic niches among the majority of the studied species.

Snail assemblages in Holocene floodplain research – an example from the southern Caucasus

Abstract. During the last decades, rivers and their deposits in different regions were intensively studied to better understand the late-Quaternary landscape evolution and former human activities. One proxy for paleoecological and paleoclimatic reconstructions is the analysis of gastropods (snails) from carbonatic river sediments. In the scope of this study, we investigated gastropod assemblages from a Holocene fluvial sediment–paleosol sequence at the upper Alazani River in the southeastern Caucasus. On the one hand, we aimed to derive reliable independent information about possible long-lasting human activity since the late Neolithic–Chalcolithic in the upper Alazani floodplain. This was formerly suggested by n-alkane biomarker vegetation reconstructions from the fluvial sediments. However, the reliability of that method is still debated. On the other hand, we aimed to obtain reliable information about a formerly suggested, possibly tectonic-driven, large-scale shift of the river course during the Late Holocene. In agreement with the n-alkane biomarkers, our results demonstrate that the studied site was free of the natural forests during the Early and Middle Holocene until ca. 4.5 cal kyr BP. Since this contrasts with a pollen-based vegetation reconstruction from a neighboring floodplain that was covered with forests during that time, the open vegetation in the upper Alazani valley was probably caused by continuous settlement activity as is also indicated by archeological finds in the sequence. Therefore, using our paleoecological proxies it is possible that we identified a settlement center in the upper Alazani floodplain that was populated from the late Neolithic–Chalcolithic. This center was not known thus far, since the settlement remains are covered by thick floodloam today that hindered their detection during archeological surface surveys. Therefore, our findings suggest that the area in the southern Caucasus region that was settled during the late-Neolithic–Chalcolithic period should have been larger than was known thus far. Furthermore, increasing contributions of wetland gastropods since ca. 4 cal kyr BP confirm a local shift of the river course towards the investigated site during the Late Holocene, possibly linked with ongoing tectonic activity. However, in contrast to former suggestions our gastropod assemblages indicate a slow rather than abrupt process. Our study demonstrates the high value of gastropod assemblages for geoarcheological and geomorphological research in floodplains with carbonatic river sediments at both a regional and local spatial scale.