Snail Abundance Research Articles

Impacts of environmental factors in rice paddy fields on abundance of the mud snail (Cipangopaludina chinensis laeta)

Impacts of environmental factors in rice paddy fields on abundance of the mud snail (Cipangopaludina chinensis laeta)

Negative indirect effects of neighbors on imperiled scleractinian corals

Predation pressure on an individual may be influenced by spatial associations with other organisms. In the case of rare and imperiled species, such indirect interactions may affect the persistence and recovery of local populations. This study examined the effects of coral neighborhood composition on the foraging behavior and impact of the corallivorous gastropod, Coralliophila abbreviata. We conducted a manipulative field experiment in which focal colonies of the threatened scleractinian coral Acropora cervicornis had no neighbors, conspecific neighbors, alternative prey (Orbicella faveolata) neighbors, or non-prey (Porites asteroides) neighbors. Individually tagged C. abbreviata were then seeded into the study area and allowed to colonize the experimental plots. Initial colonization was significantly affected by the species of neighboring corals and snail abundance after colonization was negatively correlated with focal colony growth. Snails exhibited a strong prey preference for A. cervicornis over O. faveolata and responded numerically to neighborhood quality (i.e., relative preference for neighboring corals). Thus, conspecific neighbors had the greatest predator-mediated negative effect on focal colony performance followed by O. faveolata neighbors. The results suggest that C. abbreviata mediate apparent competition between O. faveolata and A. cervicornis as both species contributed to the local abundance of their shared predator. Additionally, home range estimates for tagged C. abbreviata were calculated, compared among sexes, and found to be significantly greater for males than for females. Overall, this study sheds light on the foraging behavior of an important coral predator and highlights the potential importance of consumer-mediated indirect interactions in the dynamics of severely reduced populations. The results also have direct implications for conservation and population enhancement efforts.

The biology of Placostylus ambagiosus (Pulmonata: Bulimulidae) in New Zealand: Part 1. Behaviour, habitat use, abundance, site fidelity, homing and the dimensions of eggs and snails

The large land snail Placostylus ambagiosus (Pulmonata: Bulimulidae) was investigated during a long-term study in northernmost New Zealand. The snails fed at night on fallen leaves from a variety of broadleaf trees and bushes. During the day, most snails in shrubland rested under plants close to their food sources at densities of up to 53 snails per m2 and mean live biomasses of 47–72 g/m2. Individual snails stayed close to their food plants for up to 12 years, seldom moving away. Resting behaviour and site fidelity in forest was not investigated in detail, but some adult snails in forest returned to their original sites after being moved up to 60 m into a fenced area built to protect them from feral domestic animals. The ovoid eggs (mean 7.0 mm long×5.6 mm wide; ranges 5.5–7.7 mm long; 5.1–6.7 mm wide) were laid in clutches averaging 43 eggs (range 1–113 eggs) in shallow cavities covered with soil. More than one snail may contribute to a clutch. Adult shell height ranged from 43 mm to 97 mm and varied with habitat quality. Where snail abundance was high adults were small. Implications of these results for conservation management are discussed.

Land snail richness and abundance along a sharp ecological gradient at two sampling scales: disentangling relationships

It is generally recognized that the number of land snail species increases with the number of individuals in samples. This correlation may be an artefact of sample size, but it may also reflect the similarity in microhabitat preference of many species. Biotic interactions (competition) might also influence this relationship: an upper limit to co-existence at a particular scale. Here, we model the relationships between number of species, abundance of live individuals and environmental factors in the snail faunas of treeless fens covering a broad range of calcium content. The models considered two scales of sampling: (i) a 12 litre sample collected at a 4×4 m plot (187 samples) capturing at least 80% of the site's known species pool, and (ii) a sampling of 25×25 cm plots (115 samples) usually capturing less than 40% of the site's species pool. At the larger scale, the number of species responded to the calcium gradient more tightly than did total densities; but this was reversed at the smaller scale. Variation in abundance explained about the half of the species richness variation at both scales, but the number of individuals collected was not limiting for the number of species recorded at the larger scale. Using simulated communities we discovered that an asymptotic relationship between number of species and individuals can arise from a nested pattern of species distributions towards calcareous sites and thus that it may not be simply a rarefaction effect. The shape of a species accumulation curve may be only a weak indication of sampling efficiency when there is environmental variation among sample areas. Further, the observed hump-shaped relationship between the numbers of live individuals and species at the small scale raises a classical question about interspecific competition in land snail assemblages.

A trematode parasite alters growth, feeding behavior, and demographic success of invasive rusty crayfish (Orconectes rusticus)

Nonindigenous species can cause major changes to community interactions and ecosystem processes. The strong impacts of these species are often attributed to their high demographic success. While the importance of enemy release in facilitating invasions has often been emphasized, few studies have addressed the role of parasites in the invasive range in controlling demographic success of potential invaders. Here we examine whether a trematode parasite (Microphallus spp.) can contribute to previously documented alternate states in the abundance of invasive rusty crayfish (Orconectes rusticus) in north temperate lakes in Wisconsin, USA. Microphallus infect O. rusticus after emerging from their first intermediate host, a hydrobiid snail. As previously documented, O. rusticus reduce densities of hydrobiid snails through direct predation and destruction of macrophyte habitat. Therefore, if Microphallus substantially reduce O. rusticus fitness, these parasites may reinforce a state of low crayfish abundance, and, at the other extreme, abundant crayfish may repress these parasites, reinforcing a state of high crayfish abundance. From samples collected from 109 sites in 16 lakes, we discovered (1) a positive relationship between crayfish infection intensity and hydrobiid snail abundance, (2) a negative relationship between parasite prevalence and crayfish abundance, and (3) a negative relationship between parasite prevalence and crayfish population growth. With experiments, we found that infection with Microphallus reduced foraging behavior and growth in O. rusticus, which may be the mechanisms responsible for the population reductions we observed. Overall results are consistent with the hypothesis that Microphallus contributes to alternate states in the abundance and impacts of O. rusticus.

Effects of shorebird predation and snail abundance on an intertidal mudflat community

Top-down effects of predation are well documented in a variety of ecological communities, including marine soft-sediment systems. It has been proposed that intertidal mudflats in the upper Bay of Fundy, Canada, which host a large population of foraging shorebirds each summer, may exhibit this community dynamic. Biofilm (consisting mainly of diatoms) forms the base of the mudflat community food web, which is dominated by the amphipod Corophium volutator. To assess the potential for a trophic cascade, we conducted a manipulative field experiment examining individual and combined effects of the shorebird Calidris pusilla, a primary predator of C. volutator, and the eastern mudsnail (Nassarius obsoletus), an intraguild predator, on community structure (including macrofauna and large meiofauna retained by a 250-μm screen). Snails exhibited density-dependent top-down effects, primarily from strong negative interactions with juvenile and adult C. volutator, likely due to interference, consumption and emigration. Medium and high densities of snails reduced chlorophyll a concentration (a measure of diatom abundance), likely through consumption and disturbance of the sediment. When present at higher densities, snails also increased variability in community structure. Shorebirds were less influential in determining community structure. They reduced C. volutator biomass through consumption, but there was no resulting effect on primary production. Top-down effects of snails and birds were cumulative on C. volutator, but did not generate a trophic cascade. We suggest that a combination of omnivory and intraguild predation by shorebirds and snails, coupled with relatively low grazing pressure by C. volutator, prevented transmission of top-down effects.

Limited life-history variations in a tropical stream caenogastropod, Sulcospira hainanensis, in habitats with contrasting resource availability

Inter-population variation in the life histories of stream animals has been demonstrated to be induced by environmental differences between sites, which could be a direct consequence of differential food availability. The caenogastropod Sulcospira hainanensis (Brot, 1872) is an abundant consumer in tropical Hong Kong streams. This gonochoristic, ovoviviparous pachychilid tends to maintain higher standing stocks and productivity in less shaded sites. We hypothesized that differences in algal food availability induce diversification of life-history and demographic traits between snail populations. To test this, we compared S. hainanensis populations in four Hong Kong streams with differing conditions of shading (two shaded, two unshaded) and algal availability. Life-table analyses were also conducted for two of these snail populations in a shaded and an unshaded stream. Snails tended to grow faster and reach sexual maturity more quickly in the unshaded streams we studied, which may reflect higher assimilation of more nutritious algal food. Except for shorter life spans of snails in these unshaded streams, other re- productive and demographic attributes were mostly similar among populations; in particular, brood size and reproductive output did not appear to be strongly affected by the availability of algae. Seasonal disturbances due to wet-season spates in monsoonal Hong Kong, which appear to cause sig- nificant stochastic variability in snail abundance, may override the deterministic role of resource avail- ability and/or other environmental variables, in inducing the observed pattern of phenotypic plasticity of S. hainanensis. The present study is the first to incorporate both life-table and secondary-production analyses for a tropical stream snail. Such combined studies have rarely been undertaken on stream animals, which mainly comprise amphibiotic insects, because of the difficulty of constructing life tables for insects with biphasic life cycles and high mobility. Snails are more readily studied and we advocate the wider use of field-based life tables and production estimates in combination so as to provide greater understanding of the role of snails in energy flow and trophic dynamics.

An ecological study of Bithynia snails, the first intermediate host of Opisthorchis viverrini in northeast Thailand

Infection with the food-borne trematodiasis, liver fluke Opisthorchis viverrini, is a major public health concern in Southeast Asia. While epidemiology and parasitic incidence in humans are well studied, ecological information on the O. viverrini intermediate hosts remains limited. This study aimed to investigate the factors affecting the distribution and abundance of the first intermediate host, Bithynia siamensis goniomphalos snails. Water quality and snails were sampled in 31 sites in Muang District, Khon Kaen Province, Thailand from June 2012 to January 2013 to characterize the B.s. goniomphalos snail habitats. Species relative abundance and Shannon's diversity and evenness indices were employed to describe snail compositions and diversities across different habitat types. Statistical analyses were conducted to examine the extent to which the water quality variables and species interactions account for the relative abundance of B.s. goniomphalos snails. The results showed that the freshwater habitats of ponds, streams and rice paddies possessed significantly different abiotic water qualities, with water temperature and pH showing distinct statistical differences (P<0.05). Different habitats had different snail diversity and species evenness, with high B.s. goniomphalos snail abundance at rice paddy habitats. The differences in snail abundance might be due to the distinct sets of abiotic water qualities associated with each habitat types. The relative abundance of B.s. goniomphalos snails was found to be negatively correlated with that of Filopaludina martensi martensi snails (r=−0.46, P<0.05), underscoring the possible influence of species interaction on B.s. goniomphalos snail population. Field work observations revealed that rice planting seasons and irrigation could regulate snail population dynamics at rice paddy habitats. This study provides new ecological insights into the factors affecting Bithynia snail distribution and abundance. It bridges the knowledge gap in O. viverrini disease ecology and highlights the potential effect of anthropogenic irrigation practices on B.s. goniomphalos snail ecology.

Distribution of arid-dwelling land snails according to dryness

Although land snails are hydrophilic animals, several species inhabit arid or semi-arid environments. Here, I hypothesize that, for arid-dwelling land snails, both relatively moist environments and extreme arid zones, within their distribution ranges, should be disadvantageous. Therefore, arid-dwelling land snails should show maximal probability of presence and maximal abundances at intermediate levels of aridity. I tested this hypothesis with two land-snails from Sierra Elvira mountain range (SE Spain), Sphincterochila candidissima and Iberus gualterianus. Given that environmental variables as well as snail distribution showed spatial autocorrelation, I performed spatially explicit models, specifically simultaneous auto-regressions (SAR). The results supported the hypothesis, with the distribution of S. candidissima and the abundance of I. gualterianus following a concave-down relationship with aridity. Moreover, both species were less abundant as elevation increased, and I. gualterianus showed a positive association with rocky surface. Therefore, this study highlights that, in arid environments, arid-dwelling land snails show maximal abundance and probability of presence at intermediate aridity levels. Although the reasons explaining why extreme aridity values limit the abundance and distribution of land snails are well detailed, it remains intriguing why these snails decrease in abundance when moisture increases.

Invasion Biology Meets Parasitology: A Case Study of Parasite Spill-Back with Egyptian Fasciola gigantica in the Invasive Snail Pseudosuccinea columella

The liver fluke Fasciola gigantica is a trematode parasite of ruminants and humans that occurs naturally in Africa and Asia. Cases of human fascioliasis, attributable at least in part to F. gigantica, are significantly increasing in the last decades. The introduced snail species Galba truncatula was already identified to be an important intermediate host for this parasite and the efficient invader Pseudosuccinea columella is another suspect in this case. Therefore, we investigated snails collected in irrigation canals in Fayoum governorate in Egypt for prevalence of trematodes with focus on P. columella and its role for the transmission of F. gigantica. Species were identified morphologically and by partial sequencing of the cytochrome oxidase subunit I gene (COI). Among all 689 snails found at the 21 sampling sites, P. columella was the most abundant snail with 296 individuals (42.96%) and it was also the most dominant species at 10 sites. It was not found at 8 sites. Molecular detection by PCR and sequencing of the ITS1-5.8S-ITS2 region of the ribosomal DNA (rDNA) revealed infections with F. gigantica (3.38%), Echinostoma caproni (2.36%) and another echinostome (7.09%) that could not be identified further according to its sequence. No dependency of snail size and trematode infection was found. Both high abundance of P. columella in the Fayoum irrigation system and common infection with F. gigantica might be a case of parasite spill-back (increased prevalence in local final hosts due to highly susceptible introduced intermediate host species) from the introduced P. columella to the human population, explaining at least partly the observed increase of reported fascioliasis-cases in Egypt. Eichhornia crassipes, the invasive water hyacinth, which covers huge areas of the irrigation canals, offers safe refuges for the amphibious P. columella during molluscicide application. As a consequence, this snail dominates snail communities and efficiently transmits F. gigantica.

Value-chain analysis of freshwater apple snail (Pila globosa) used for on-farm feeds in the freshwater prawn farming sector in Bangladesh

Growth of the freshwater prawn (Macrobrachium rosenbergii) sector in Bangladesh since 1970s has been supported by natural availability of freshwater apple snail (Pila globosa), used for on-farm prawn feeds. The present study identified the current configuration of the value-chain benefits and constraints of freshwater apple snail in south-western Bangladesh in August 2011, based upon Rapid Market Appraisal (RMA) approach. The site of snail collection was Chanda Beel in Gopalganj district, while trading, processing and final consumption was represented by Rayer Mahal Bazar in Khulna district. There were seven different nodes recognized throughout the value chain. Snail marketing was identified as a seasonal business and took place during June to November each year. Between 1995 and 2011 the price of whole snail, meat and shell has increased by 800%, 325% and 315%, respectively. The abundance of snail had been reduced and its demand has increased due to the expansion of the prawn farming industry. Prawn farmers preferred snail meat due to its’ low cost (US$ 0.21 kg-1) as a source of protein compared to commercial prawn feed (US$ 0.41 kg-1). Snail harvesting and processing were considered as additional livelihood options for the poor, where 60% of the labour involved in snail harvesting were women, and 95% the de-shelling workforce. Induced breeding in captivity and sustainable management in nature as well as development of commercial production of apple snails might reduce the pressure on ecosystems and positively contributed to the continued expansion of freshwater prawn farming in Bangladesh. DOI: http://dx.doi.org/10.3329/ijarit.v3i2.17840 Int. J. Agril. Res. Innov. &amp; Tech. 3 (2): 22-30, December, 2013

Utilization of the invasive alga Gracilaria vermiculophylla (Ohmi) Papenfuss by the native mud snail Ilyanassa obsoleta (Say)

The recent invasions of the red alga, Gracilaria vermiculophylla, to the Atlantic and Eastern Pacific Oceans have the potential to significantly alter intertidal and subtidal soft sediment communities. In particular, G. vermiculophylla increases habitat complexity and provides a novel hard substrate in an otherwise two dimensional habitat. Following our observations that the native omnivorous mud snail Ilyanassa obsoleta utilizes G. vermiculophylla for egg capsule deposition, our field surveys demonstrated that the in situ abundance of egg capsules on G. vermiculophylla matched abundances on a native alga Ceramium virgatum and were at least 11–50 times greater than on all other co-occurring macrophytes. Additionally, through mesocosm experiments, we showed that I. obsoleta preferentially deposits eggs on the invasive G. vermiculophylla over native substrates. However, despite the thick layer of egg capsules found on G. vermiculophylla, no detrimental effects were seen on thalli growth. In contrast, growth of the native red alga Ceramium virgatum was significantly reduced when egg capsules were present, suggesting G. vermiculophylla can out-compete native macrophytes in areas of I. obsoleta abundance, while facilitating reproduction of the native mud snail. This novel interaction has the potential to significantly alter biological interactions in soft sediment communities through a variety of different mechanisms, including the alteration of trophic cascades via the increase in mud snail abundance. Furthermore, facilitation of the reproductive success of I. obsoleta may lead to increases in the occurrence of cercarial dermatitis, as I. obsoleta is a known intermediate host organism.

Distribution and abundance of schistosomiasis and fascioliasis host snails along the Mara River in Kenya and Tanzania

We purposively selected 39 sampling sites along the Mara River and its two perennial tributaries of Amala and Nyangores and sampled snails. In addition, water physicochemical parameters (temperature, turbidity, dissolved oxygen, conductivity, alkalinity, salinity and pH) were taken to establish their influence on the snail abundance and habitat preference. Out of the 39 sites sampled, 10 (25.6%) had snails. The snail species encountered included Biomphalaria pfeifferi Krauss – the intermediate host of Schistosoma mansoni Sambon, Bulinus africanus – the intermediate host of Schistosoma haematobium, and Lymnaea natalensis Krauss – the intermediate host of both Fasciola gigantica and F. hepatica Cobbold. Ceratophallus spp., a non-vector snail was also encountered. Most (61.0%) of the snails were encountered in streamside pools. Schistosomiasis-transmitting host snails, B. pfeifferi and B. africanus, were fewer than fascioliasis-transmitting Lymnaea species. All the four different snail species were found to be attached to different aquatic weeds, with B. pfeifferi accounting for over half (61.1%) of the snails attached to the sedge, followed by B. africanus and Lymnaea spp., accounting for 22.2 and 16.7%, respectively. Ceratophallus spp. were non-existent in sedge. The results from this preliminary study show that snails intermediate hosts of schistosomiasis and fascioliasis exists in different habitats, in few areas along the Mara River, though their densities are still low to have any noticeable impacts on disease transmission in case they are infected. The mere presence of the vector snails in these focal regions calls for their immediate control and institution of proper regulations, management, and education among the locals that can help curtail the spread of the snails and also schistosomiasis and fascioliasis within the Mara River basin.

Composición y estructura en agregaciones de moluscos terrestres en el Complejo de vegetación de mogote, Escaleras de Jaruco, Cuba

Cuba has one of the richest land snail faunas of the world. This important fact has promoted different kind of studies on this group to promote conservation programs, from which many studies have directed their efforts to inventories, and population and community ecology. To contribute with this population knowledge, we studied land snails assemblages in three karstic elevations at the "Escaleras de Jaruco-Tapaste-Cheche" Natural Protected Landscape, Mayabeque, Cuba. We aimed to analyze the variation of the composition and structure of the assemblages between the rainy and little rainy months. The study was conducted from August to November 2009 and from January to April, 2010, in ten permanent square plots (9 m2) separated for over 20 m, on each elevation (Beluca, La Chirigota and La Jaula). In each plot, only live individuals were registered (physiologically active and at rest) to obtain species richness and abundance; besides, temperature (degree C) and relative humidity (%) were also considered in each plot. A total of 4248 individuals were observed which comprised two subclasses, five orders, 11 families, 20 genera and 21 species of terrestrial molluscs. From the total, 19 were Cuban endemics and eight were exclusive from Mayabeque, Matanzas. The Jaula showed the greater riches with 19 species, followed of Beluca with 17, and The Chirigota with 15. In the rainy months, La Jaula, showed individual's greater abundance with 1707, followed of Beluca with 1305 and La Chirigota with 1236. We observed differences in the population density in the three elevations between the rainy and little rainy months, which can be due to the climatic adverse conditions that are shown at the little rainy months. Additionally, during the survey we observed dominance of prosobranch species over the pulmonates. The specific abundance curves showed a steep slope, although was major in the rainy months in relation to the little rain months, which indicates the presence of dominant, common and rare species in the assemblages. In this study, it was demonstrated than the riches and the abundance of land snails in all three elevations, was favored for the elevated relative humidity and the air temperature during the rainy months. These environmental conditions resulted fundamental for the survival of these terrestrial gastropods, as the reproduction and search of food were favored.

Scientific Opinion on the assessment of the potential establishment of the apple snail in the EU

EFSA requested the PLH Panel to review the current state of the art of the biology and ecology of apple snails, reported in this opinion, and to perform an environmental risk assessment for validation of the Plant Health environment guidance document, which will be provided in a second opinion. The Panel presents in this opinion the current state of the art of the biology of apple snails, and develops and uses a population dynamics model to assess the potential establishment of apple snails in the EU. A thorough review of the literature on the biology of Pomacea canaliculata and P. maculata was performed to collect information and data on life history characteristics related to temperature, which was used in the population dynamics model. Although uncertainties on the systematics and taxonomy of the genus Pomacea remain, it is now acknowledged that Pomacea insularum is a synonym of P. maculata and can be undoubtedly differentiated from P. canaliculata. Natural spread occurs via rivers and canals, in which the snails crawl, drift, float and raft. Flooding increases spread. In addition, attachment to animals (e.g. birds, cattle, horses, deer and aquatic invertebrates) results in spread. Human assistance results in spread through cultivation transport of rice seedlings, aquaculture, aquaria, boats, and agricultural field machinery. The potential distribution of P. canaliculata in Europe was obtained by calculating with the population dynamics model, the average snail abundance per year in each node of a grid of 0.25 × 0.25 degrees covering Europe, which resulted in the following conclusions: (1) the area of potential establishment comprises wetlands of southern Europe (i.e. Spain, southern France, most of Italy and Greece) and the Balkans up to the latitude of the Danube river, (2) the potential area of establishment includes the rice production areas in Europe. © European Food Safety Authority, 2013

A manipulative study of macroinvertebrate grazers in Hong Kong streams: do snails compete with insects?

Summary Sulcospira hainanensis (Pachychilidae) is the most abundant snail in Hong Kong streams. It constitutes about 1% of total benthic macroinvertebrate abundance but, because of its relatively large size, can comprise over one‐third of standing biomass. This snail may have the potential to depress periphytic algae and thereby compete for food with insect grazers. Possible competitive interactions were investigated by manipulating snail densities in 4 streams under different shading conditions (2 shaded, 2 unshaded). Since previous work in Hong Kong streams indicated that algal standing stocks were depleted by wet‐season spates, manipulations were carried out during both the wet and dry seasons to investigate the extent of variability in interaction intensity. Insect colonisation on artificial substrata (tiles) was compared between treatments where wire mesh barriers limited snail access, and under control conditions of natural snail densities. The exclusion treatment reduced snail densities by about 30–50% relative to controls during both seasons. Algal densities were lower during the wet season in two streams, probably reflecting spate‐induced disturbance, but snail densities remained relatively stable throughout the study. Strong effects of S. hainanensis on algae and insects were observed during the dry season, with higher algal biomass and insect densities (especially mayflies) in snail‐exclusion treatments. Differences between treatments during the wet season were generally minor. Snails depressed algae more severely in shaded streams, but this did not result in greater increases in insect abundance in snail‐exclusion treatments. Evidently snails did exert competitive effects on insects, but spate‐induced disturbance during the wet season appeared to override this biotic interaction, in agreement with predictions of the harsh‐benign hypothesis. Competition intensity was unaffected by shading conditions, perhaps because other environmental factors moderated interaction intensity in shaded streams.

Riparian-Associated Gastropods in Western Washington: Community Composition and the Effects of Forest Management

We evaluated the abundance of riparian gastropod communities along headwater streams and their response to logging in southwestern Washington State. Terrestrial mollusks near logged streams with ∼15 m fixed-width buffers were compared to logged streams with no buffers and to unlogged controls. Mollusk communities varied among sites relative to vegetative composition, the amount of understory cover and presence of seeps or small wetland features in the riparian areas. After logging, slug and snail abundance were significantly different between streams with no buffers compared to fixed-width buffers and control streams, however the effect size was relatively small suggesting site variability may override the effects of logging. Our findings illustrate that site variability can affect mollusk community structure and influence taxa resiliency to disturbances such as logging.

Are Temperate Land Snails Susceptible to Climate Change Through Reduced Altitudinal Ranges? A Pennsylvania Example.

Distributions of some plants and animals have already shifted in recent years due to climate warming, and climate warming has potential to extirpate populations of taxa that cannot easily move or adapt to changes in temperatures and/or moisture. This study in Pennsylvania, U.S.A. focuses on whether snail populations currently confined to cooler habitats at higher elevations (elevations 700–978 m comprise only 2% of Pennsylvania's area) might decline or be eliminated if their ranges are reduced upward by climate warming. We examined whether some land snail species are limited to upper elevations in order to assess whether climate warming poses a threat to them. Sampling included 108 sites across Pennsylvania, comprising 12 localities at each of nine elevations from 100 to 900 m elev. Overall numbers of snail species and abundances decreased at greater elevations. Most individual species tended to occur throughout sampled elevations or occurred primarily at lower elevations, so the reduced altitudinal range aspect of climate warming might not threaten them. However, five species occurred significantly more often at greater elevations suggesting that their populations might decline if climate warming were to reduce their ranges upward. Four additional species including three native slugs showed non-significant trends to occur at higher elevations. These species might be monitored into the future.

Response of mangroves to drought and non-tidal conditions in St Lucia Estuary, South Africa

The effect of a prolonged closed-mouth state on the condition of mangrove habitats was studied in May 2010 at St Lucia Estuary, KwaZulu-Natal. The mouth had been closed to the sea since 2002 as a result of artificial mouth closure and drought, which had resulted in non-tidal, dry and hypersaline aquatic conditions. Sediment characteristics, mangrove population structure, and snail and crab abundance, were measured at four sites of differing salinity and water level to determine if there was a relationship between environmental characteristics and biotic response. A site fringing the main channel had the lowest elevation and the highest density of mangrove seedlings and saplings at the water's edge, whereas a dry site at the highest elevation had the lowest density of mangroves with mostly tall adult trees and few saplings. At these two sites the salinity (>34.5) was significantly higher and the surface sediment water content (<30%) was significantly lower than at other sites. Highest tree density was found at a freshwater seepage site, where all size classes were represented, while the permanently flooded site between the Mfolozi River and St Lucia Estuary had the tallest trees but no seedlings or saplings. At the freshwater seepage and permanently flooded sites, porewater and sediment salinity (<10) were significantly lower, while sediment moisture (>55.5%) was significantly higher, than at the fringing and dry sites. Low sediment moisture was unfavourable for mangrove growth and recruitment. Long-term monitoring is needed to document the response of the mangroves to closed-mouth, non-tidal conditions.

Assessment of the effects of nickel on benthic macroinvertebrates in the field

A field-based evaluation of the biological effects of potential nickel (Ni) exposures was conducted using monitoring data for benthic macroinvertebrates and water chemistry parameters for streams in England and Wales. Observed benthic community metrics were compared to expected community metrics under reference conditions using RIVPACS III+ software. In order to evaluate relationships between Ni concentrations and benthic community metrics, bioavailable Ni concentrations were also calculated for each site. A limiting effect from Ni on the 90th percentile of the maximum achievable ecological quality was derived at "bioavailable Ni" exposures of 10.3μgl(-1). As snails have been identified as particularly sensitive to nickel exposure, snail abundance in the field in response to nickel exposure, relative to reference conditions, was also analysed. A "low effects" threshold for snail abundance based on an average of spring and autumn data was derived as 3.9μgl(-1) bioavailable Ni. There was no apparent effect of Ni exposure on the abundance of Ephemeroptera (mayflies), Plecoptera (stoneflies) or Tricoptera (caddisflies) when expressed relative to a reference condition within the range of "bioavailable Ni" exposures observed within the dataset. Nickel exposure concentrations co-vary with the concentrations of other stressors in the dataset, and high concentrations of Ni are also associated with elevated concentrations of other contaminants.