Snail Growth Research Articles

Testing Antarctic resilience: the effects of elevated seawater temperature and decreased pH on two gastropod species

AbstractOcean acidification has been hypothesized to increase stress and decrease shell calcification in gastropods, particularly in cold water habitats like the western Antarctic Peninsula (WAP). There is limited information on how calcified marine benthic invertebrates in this region will respond to these rapidly changing conditions. The present study investigated the effects of elevated seawater temperature and decreased pH on growth (wet mass and shell morphometrics), net calcification, and proximate body composition (protein and lipid) of body tissues in two common benthic gastropods. Individuals of the limpet Nacella concinna and the snail Margarella antarctica collected from the WAP were exposed to seawater in one of four treatment combinations: current ambient conditions (1.5°C, pH 8.0), near-future decreased pH (1.5°C, pH 7.8), near-future elevated temperature (3.5°C, pH 8.0), or combination of decreased pH and elevated temperature (3.5°C, pH 7.8). Following a 6-week exposure, limpets showed no temperature or pH effects on whole body mass or net calcification. Despite no significant differences in whole body mass, the shell length and width of limpets at elevated temperature tended to grow less than those at ambient temperature. There was a significant interaction between the sex of limpets and pH. There were no significant temperature or pH effects on growth, net calcification, shell morphologies, or proximate body composition of snails. Our findings suggest that both gastropod species demonstrate resilience to initial exposure to temperature and pH changes predicted to occur over the next several hundred years globally and perhaps sooner along the WAP. Despite few significant impacts of elevated temperature or decreased pH, any response to either abiotic variable in species with relatively slow growth and long lifespan is of note. In particular, we detected modest impacts of reduced pH on lipid allocation in the reproductive organs of the limpet N. concinna that warrants further study.

Mercury toxicity to terrestrial snails in a partial life cycle experiment

Despite growing concerns about the potential adverse effects of elevated mercury (Hg) concentrations in the terrestrial environment, only a few toxicity data are available for soil invertebrates. The chronic toxicity of inorganic Hg-Hg(II)--through food or soil contaminations was therefore assessed for the snail Cantareus aspersus, a well-recognized soil quality bioindicator. The 28-day EC50s (the concentrations causing 50% effect) for the snail growth were 600 and 5048 mg Hg kg(-1) for food and soil, respectively. A survey of growth over its entire duration (91 days) allowed to show that the effects took place rapidly after the beginning of exposure and persisted in the long term. Reproduction was also impaired, and we established 28-day EC50s for sexual maturation and fecundity of 831 and 339 mg Hg kg(-1), respectively, for food and 1719 and 53 mg Hg kg(-1), respectively, for soil. Total Hg analyses in snails exposed to contaminated matrices revealed important bioaccumulation capacities up to 2000 mg Hg kg(-1) viscera. Critical limits in internal Hg concentration of about 500 and 1000 mg Hg kg(-1) were determined as thresholds for the induction of growth toxicity through food and soil exposure, respectively. These different values underlined differences in the uptake and toxicological dynamics of Hg according to its bioavailability in the source of exposure.

Kelp in hot water: II. Effects of warming seawater temperature on kelp quality as a food source and settlement substrate

ABSTRACT: Predicting the effect of climate change on communities requires an understanding ofthe effects of environmental conditions on species and their interactions. We investigated thepotential for warming seawater temperature to modify the interactions of the gastropod meso-grazer Lacuna vincta and the invasive bryozoan Membranipora membranacea with kelps in NovaScotia. The nutritional content (C/N) of the kelps Saccharina latissima, Laminaria digitata andAgarum clathratum were unaffected by temperature (11, 18 and 21°C), and chemical defenses(phlorotannins) were reduced only in A. clathratum after 1 wk exposure to 21°C. C/N and phloro-tannin content increased over the season in S. latissima collected monthly in summer 2013 and2014. The effect of temperature-induced changes in kelp on the grazing of L. vincta was assessedusing feeding experiments with S. latissima pretreated at 11 or 21°C. Snails consumed more kelppretreated at 21°C only when grazing rate was high. The quality of S. latissima as a food sourcefor L. vincta was not affected by temperature, as diets of kelp pretreated at 11 and 21°C supportedsimilar growth, reproduction, and survival of snails. Temperature also did not affect the quality ofkelp as a substrate for M. membranacea, since settlement rates were not different betweenS. latissima pretreated at ambient temperature (9 to 14) and 21°C. The absence of temperature-induced changes in kelp quality suggests that the effects of L. vincta and M. membranacea will actadditively with the direct effects of temperature and cause increased biomass loss from kelp beds.KEY WORDS: Kelp · Climate change · Temperature · Saccharina latissima · Lacuna vincta ·Herbivory · Membranipora membranacea · Bryozoans

Trematode maturation patterns in a migratory snail host: What happens during upshore residency in a Mediterranean lagoon?

Maturation of trematode larval stages is expected to be temporally and spatially adapted to maximise the encounter with the adequate downstream host, i.e. the host, which will be infected by this parasite stage. Since studies on intramolluscan parasite maturation are scarce but important in the context of parasite transmission, the larval development inside sporocysts was monitored during upshore residency of the snail host Gibbula adansonii (Trochidae), i.e., from March to May (2011 and 2013), when these snails temporarily reside in the intertidal habitat of a Western Mediterranean lagoon (40° 37' 35″ N, 0° 44' 31″ E, Spain). Data on the relative quantity of different maturation stages of Cainocreadium labracis and Macvicaria obovata (Opecoelidae) parasitising the G. adansonii as well as on snail and sporocyst size were explored using linear models and linear mixed models. The effect of the trematodes on snail growth was shown to be species-specific, with snail and sporocyst size acting as proxies of the reproductive capacity of M. obovata but not that of C. labracis. The number of cercarial embryos and germinal balls did not show monthly variation in either parasite species, but a higher number of mature stages and the highest maturity index was found in April. Hence, during the snail's limited spawning-related presence in the upshore waters of the lagoon, continuous production and output of infectious cercariae was observed, which indicates a link between larval maturation and snail migration. The synchronization of snails, mature parasite transmission stages and downstream hosts in time and space guarantees a successful completion of the life cycle.

What can aquatic gastropods tell us about phenotypic plasticity? A review and meta-analysis.

There have been few attempts to synthesise the growing body of literature on phenotypic plasticity to reveal patterns and generalities about the extent and magnitude of plastic responses. Here, we conduct a review and meta-analysis of published literature on phenotypic plasticity in aquatic (marine and freshwater) gastropods, a common system for studying plasticity. We identified 96 studies, using pre-determined search terms, published between 1985 and November 2013. The literature was dominated by studies of predator-induced shell form, snail growth rates and life history parameters of a few model taxa, accounting for 67% of all studies reviewed. Meta-analyses indicated average plastic responses in shell thickness, shell shape, and growth and fecundity of freshwater species was at least three times larger than in marine species. Within marine gastropods, species with planktonic development had similar average plastic responses to species with benthic development. We discuss these findings in the context of the role of costs and limits of phenotypic plasticity and environmental heterogeneity as important constraints on the evolution of plasticity. We also consider potential publication biases and discuss areas for future research, indicating well-studied areas and important knowledge gaps.

Effects of sewage sludge amendment on snail growth and trace metal transfer in the soil-plant-snail food chain.

Cu, Zn, Pb, and Cd concentrations in a soil plant (Lactuca sativa) continuum were measured after sewage sludge amendment. The effects of sewage sludge on growth and trace metal bioaccumulation in snails (Cantareus aspersus) were investigated in a laboratory experiment specifically designed to identify contamination sources (e.g., soil and leaves). Application of sewage sludge increased trace metal concentrations in topsoil. However, except Zn, metal concentrations in lettuce leaves did not reflect those in soil. Lettuce leaves were the main source of Zn, Cu, and Cd in exposed snails. Bioaccumulation of Pb suggested its immediate transfer to snails via the soil. No apparent toxic effects of trace metal accumulation were observed in snails. Moreover, snail growth was significantly stimulated at high rates of sludge application. This hormesis effect may be due to the enhanced nutritional content of lettuce leaves exposed to sewage sludge.

Efecto de la espirulina (Arthrospira platensis) (Oscillatoriales: Cyanobacteria) en la cría experimental de Pseudosuccinea columella (Basommatophora: Lymnaeidae)

<p>Snails of the family Lymnaeidae, as <em>Pseudosuccinea columella</em>, are the intermediate hosts of <em>Fasciola hepatica</em>, the causative agent of fasciolosis in human and livestock all over the world. A thorough knowledge of snail biology is essential for describing the transmission dynamics and for controlling this disease. Since food quality has had a significant effect on snail growth, fecundity and fertility, in this study we evaluated the use of spirulina (<em>Arthrospira platensis</em>) as a food resource for the artificial breeding of <em>P. columella</em>, an invasive snail and the main intermediate host of <em>F. hepatica</em> in Northeastern Argentina. The main purpose was to measure the effect of spirulina on fitness parameters such as survival rate, growth rate, size at first reproduction, lifetime fecundity and viable offspring. A total of 20 676 newly-laid F<sub>2</sub> eggs were used; half of them were fed with lettuce (treatment L) and the other half with lettuce plus spirulina (treatment L+S). In comparison with <em>P. columella</em> snails fed only with lettuce, we found that <em>P. columella</em> fed with lettuce plus spirulina: <strong>1)</strong> showed higher survival rates, <strong>2)</strong> grew faster and showed higher growth increments, <strong>3)</strong> attained sexual maturity earlier in time (L+S:60 days vs. L:120 days) and at a smaller size (L+S:4.8mm vs. L:8.2mm), <strong>4)</strong> had a longer reproductive period (L+S:150 days vs. L:90 days), <strong>5)</strong> produced a higher number of eggs/snail (L+S:29.6 vs. L:13.3), and <strong>6)</strong> showed a higher offspring hatching rate (L+S:70% vs. L:40%). The supplementation of <em>P. columella</em> diet with commercial spirulina enhances it fitness and improved the artificial breeding of this species. Spirulina may have a direct positive effect on <em>P. columella</em> development by consuming it, along with an indirect positive effect by improving the water quality. This rearing technique provided large number of reproducing adults and a continuous production of offspring, which are essential for developing future experimental studies in order to improve our knowledge on <em>P. columella</em> biology.</p>

The effects of the herbicide atrazine on freshwater snails.

Atrazine has been shown to affect freshwater snails from the subcellular to community level. However, most studies have used different snail species, methods, endpoints, and atrazine exposure concentrations, resulting in some conflicting results and limiting our understanding. The goal of this study was to address these concerns by (1) investigating the acute and chronic effects of atrazine on four species of freshwater snails (Biomphalaria glabrata, Helisoma trivolvis, Physa acuta, and Stagnicola elodes) using the same methods, endpoints, and concentrations, and (2) summarizing the current literature pertaining to the effects of atrazine on freshwater snails. We conducted a 48 h acute toxicity test with an atrazine concentration higher than what typically occurs in aquatic environments (1000 µg/L). Additionally, we exposed snails to environmentally relevant atrazine concentrations (0, 0.3, 3, and 30 µg/L) for 28 days and assessed snail survival, growth, and reproduction. We also summarized all known literature pertaining to atrazine effects on freshwater snails. The literature summary suggests snails are often affected by environmentally relevant atrazine concentrations at the subcellular and cellular levels. These effects are typically not transitive to effects on survival, growth, or reproduction at the same concentrations. Our acute exposures corroborate the general trend of no direct effect on snail populations as atrazine did not directly affect the survival of any of the four snail species. Similarly, environmentally relevant concentrations did not significantly affect the survival, growth, or reproduction of any snail species. These results indicate that, in the absence of other possible stressors, the direct effects of environmentally relevant atrazine concentrations may not be realized at the snail population level.

Reciprocal transplant reveals trade-off of resource quality and predation risk in the field.

Balancing trade-offs between avoiding predators and acquiring food enables animals to maximize fitness. Quantifying their relative contribution to vital rates in nature is challenging because predator abundance and nutrient enrichment are often confounded. We employed a reciprocal transplant study design to separate these confounded effects on growth and reproduction of snails at wetland sites along a gradient of predator threats and phosphorus (P) enrichment associated with a canal. We held snails in mesh bags that allowed the passage of waterborne predator cues and fed them local or transplanted periphyton. Molluscivores were more abundant near the canal, and snails tethered near the canal suffered 33% greater mortality than those tethered far from it (far sites). The greatest difference in snail growth rates was at the far sites where growth on far periphyton was 48% slower than on P-enriched (near canal) periphyton. Close proximity to the canal reduced growth on near periphyton by 21% compared to growth on the same periphyton far from the canal; there was no difference in growth rate on either periphyton type when snails were raised near the canal. Snails laid 81% more egg masses at far sites than at near sites, regardless of periphyton origin. Top-down and bottom-up processes were elevated near the canal, and their effects canceled on growth, but not reproduction. Phenotypic trade-offs such as these may explain why some taxa show little response to nutrient enrichment, compared to others, or that the effects of nutrient enrichment may be context dependent.

Studies on the molluscicidal activity of Agave angustifolia and Pittosporum tobira on schistosomiasis transmitting snails.

In the search for new molluscicidal plants for controlling the snail vectors of schistosomiasis, laboratory evaluation was made to assess the molluscicidal activity of Agave angustifolia and Pittosporum tobira plants against Biomphalaria alexandrina snails. Results indicated that both plants have promising molluscicidal activity as the LC90 of the dry powder of both plants was 120 ppm. Both plants showed marked cercaricidal and miracidicidal potencies against S. mansoni larvae. The LC90 of both plants (120 ppm) killed most B. alexandrina eggs within 24 h of exposure. The sub-lethal concentrations of both plants markedly suppressed the survival rate of B. alexandrina snails and the mortality increased with increasing the concentrations and the exposure period up to 10 successive weeks. The accumulative toxic effect of these concentrations was continuous during the recovery period. Also, the reproductive rates of exposed snails were greatly affected even through the recovery period. This depression in reproductive ability of snails was accompanied by histological damage in the hermaphrodite glands of exposed snails. Meanwhile, the growth of snails was estimated weekly and it showed great inhibition in exposed snails comparing with the control ones.

Influence of season, temperature, and photoperiod on growth of the land snail Helix aperta

Growth strategies are often plastic and influenced by environmental conditions. Terrestrial gastropods are particularly affected by seasonal and climatic variables, and growth rate and size at maturity are key traits in their life history. Therefore, we investigated juvenile growth of Helix aperta snails under four combinations of temperature and photoperiod using two sets of young snails, born in the laboratory from adults collected in either the autumn (aestivating snails) or spring (active snails). Parental snails were collected from Bakaro (Northeastern Algeria). Higher temperature increased adult size and reduced the time to first reproduction. Long day photoperiod also increased the final body weight, but had no effect on the length of the growth period. The season of birth had significant effects on length of the growth period and weight of hatchlings, whereas this weight difference disappeared by adulthood. The Spring snails took less time to develop and reached similar adult body weight as the Autumn snails. These differences may be owing to differences in egg size or quality between the snails from different seasons. More rapid growth in Spring snails results in larger snails entering aestivation, a period with size-related mortality in this species.

Use of Tuna-Cooking Liquid Effluent as a Dietary Protein and Lipid Source Replacing Fishmeal in Formulated Diets for Growing Hatchery-Reared Juvenile Spotted Babylon (Babylonia areolata)

This study presented the first research conducted on the use of tuna by-product from the tuna canning industry for growing hatchery-reared juvenile spotted babylon (Babylonia areolata) to marketable sizes. A feeding trial was conducted to evaluate the effects of five levels of partial to complete replacement of fishmeal by tuna-cooking liquid effluent on growth performance and body composition of snails reared under a flow-through culture system over 150 days. Five experimental diets were formulated to contain 0%, 25%, 50%, 75%, and 100% of tuna-cooking liquid effluent (diets TCLE0, TCLE25, TCLE50, TCLE75, and TCLE100, respectively). Results showed that significant differences (P 0.05) in final survival rate was found among snails fed all experimental diets. Survival rates ranged from 94.2%-94.6%. Moreover, the snails fed diets of 100% replacement of fishmeal by tuna-cooking liquid effluent meal (TCLE100) showed the highest protein content, lowest lipid content, and lowest cholesterol content compared with snails fed all the other diets. The whole body composition of snails fed TCLE50 was significantly higher (P<0.05) in saturated fatty acid, monounsaturated fatty acid, polyunsaturated fatty acid, unsaturated fatty acid, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachinodic acid (ARA), n-6 PUFA, and n-3 PUFA contents than the groups of snails fed all the other diets The results of this study indicated that tuna-cooking liquid effluent meal can completely replace fishmeal protein with positive effects on snail growth performance and whole body composition.

Replacement of Fishmeal by Poultry By-Product Meal in Formulated Diets for Growing Hatchery–Reared Juvenile Spotted Babylon (Babylonia areolata)

A feeding trial was conducted to evaluate the effects of five levels of partial to total replacement of fishmeal by poultry by–product meal on growth performance and body composition of hatchery–reared juvenile spotted babylon (Babylonia areolata) under aflow-through culture system over 150 days. Five experimental diets were formulated to contain 0%, 25% 50%, 75% and 100% of gradient poultry by-product meal (diet PBM0, PBM25, PBM50, PBM75 and PBM100, respectively). Significant differences (P 0.05) while snails fed diets of PBM0 and PBM100 showed poorer specific growth rates of 2.03-2.12% day-1, respectively. Final survival rates of the snails ranged from 92.73% -93.94% and did not differ significantly (P>0.05) between feeding treatments. Significant differences (P<0.05) were detected in proximate composition (protein, ash, fat, moisture, and carbohydrate, cholesterol content, amino acid composition and fatty acid composition of the whole flesh of experimental snails among all feeding treatment groups. Snails fed diets of PBM-50 resulted in the highest protein and fat contents compared with snails fed the PBM0, PBM25, PBM75 and PBM100 replacement diets. Cholesterol was significantly lower (P<0.05) in snails fed diets of PBM75 and PBM100 than in snails fed diets PBM0, PBM25, and PBM50. The whole body composition of snails fed diet of PBM75 was significantly higher (P<0.05) in total non-essential amino acids and total essential amino acids than those of snails fed PBM0, PBM25, PBM100, and PBM75. The whole body composition of snails fed PMB-50 was significantly higher (P<0.05) regarding EPA, DHA, ARA, n-6 PUFA, and n-3 PUFA contents than those of snails fed PBM0, PBM25, PBM100, and PBM75. The results of this study indicated that poultry by-product meal can replace fishmeal protein by 50-75% with no negative effects in snail growth performance. Moreover, the inclusion of up to 75% poultry by-product meal in the diet improved feed efficiency and body composition.

Sewage sludge application in a plantation: Effects on trace metal transfer in soil–plant–snail continuum

We studied the potential bioaccumulation of Cu, Zn, Pb and Cd by the snail Cantareus aspersus and evaluated the risk of leaching after application of sewage sludge to forest plantation ecosystems. Sewage sludge was applied to the soil surface at two loading rates (0, and 6tonsha−1 in dry matter) without incorporation into the soil so as to identify the sources of trace metal contamination in soil and plants and to evaluate effects on snail growth. The results indicated a snail mortality rate of less than 1% during the experiment, while their dry weight decreased significantly (<0.001) in all treatment modalities. Thus, snails showed no acute toxicity symptoms after soil amendment with sewage sludge over the exposure period considered. Additions of sewage sludge led to higher levels of trace metals in forest litter compared to control subplots, but similar trace metal concentrations were observed in sampling plants. Bioaccumulation study demonstrated that Zn had not accumulated in snails compared to Cu which accumulated only after 28days of exposure to amended subplots. However, Pb and Cd contents in snails increased significantly after 14 and 28days of exposure in both the control and amended subplots. At the last sampling date, in comparison to controls the Cd increase was higher in snails exposed to amended subplots. Thus, sludge spread therefore appears to be responsible for the observed bioaccumulation for Cu and Cd after 28days of exposure. Concerning Pb accumulation, the results from litter–soil–plant compartments suggest that soil is this metal's best transfer source.

Sublethal effects of the beta-blocker sotalol at environmentally relevant concentrations on the New Zealand mudsnail Potamopyrgus antipodarum.

Monitoring sublethal effects of pharmaceuticals on nontarget species in aquatic environments has become an important topic in ecotoxicology, yet few studies have been conducted concerning the effects of beta-blockers on aquatic organisms. The present study investigated the effects of the beta-blocker sotalol (SOT) at 3 environmentally relevant concentrations on life-history traits of the New Zealand mudsnail Potamopyrgus antipodarum. Based on the pharmacodynamic properties of SOT, the authors hypothesized reduced numbers of embryos in the brood pouches, decelerated growth of adult snails, and smaller size of neonates, but no effect on mortality rates of adults. Contrary to the hypothesis, the total number of embryos was significantly higher after 56 d of exposure at nominal concentrations of 0.05 µg/L and 1.0 µg/L by 107% and 73%, respectively. No differences in embryo numbers were observed at earlier time-points. Therefore, the mode of action seems to be an extension of the reproductive period rather than an increase of the embryo production. Furthermore, our results indicate a hormetic dose-response relationship, because no effects were observed at the highest test-concentration (6.5 µg/L). Mortality, growth of adult snails, and neonate sizes were not affected by the beta-blocker. Given the strong influence on reproduction, the effects of sublethal concentrations of SOT and other beta-blockers deserve better consideration in ecotoxicological risk assessment.

Bioaccumulation and effects of different-shaped copper oxide nanoparticles in the deposit-feeding snail Potamopyrgus antipodarum.

Copper oxide (CuO) nanoparticles (NPs) are among the most widely used engineered NPs and are thus likely to end up in the environment, predominantly in sediments. Copper oxide NPs have been found to be toxic to a variety of (mainly pelagic) organisms, but to differing degrees. In the present study, the influence of CuO NP shape on bioavailability and toxicity in the sediment-dwelling freshwater gastropod Potamopyrgus antipodarum was examined. In 2 separate studies, snails were exposed to either clean sediment or sediment spiked with either aqueous Cu or CuO NPs of different shapes (rods, spheres, or platelets) at 240 µg Cu/g dry weight of sediment (nominal). In neither of the studies was survival found to be related to Cu form (i.e., free ion vs particle) or shape, whereas snail growth was severely influenced by both form and shape. Reproduction was affected (by CuO NP spheres and aqueous Cu) only when estimated as the total number (live plus dead) of juveniles produced per snail per week. Both the aqueous and particulate forms of Cu were available for uptake by snails when mixed into sediment. However, Cu body burden was not directly related to observed effects. The present study stresses the need for both a better understanding of uptake mechanisms and internal distribution pathways of NPs and an assessment of long-term consequences of NP exposure.

Tolerance of embryos and hatchlings of the invasive apple snail Pomacea maculata to estuarine conditions

One of the most successful groups of invasive consumers worldwide is freshwater snails of the family Ampullariidae, including Pomacea maculata, yet little is known about snail survival and growth in the range of conditions found in estuarine ecosystems. Here, we provide an experimental assessment of P. maculata survivability in estuarine conditions, documenting: (1) egg susceptibility to tidal inundation (2) salinity tolerance of snails, and (3) salinity effects on hatchling growth. Results indicate that estuarine conditions will not limit apple snail colonization in oligohaline and mesohaline reaches of estuaries, with eggs remaining viable when exposed to periodic inundations typical of a tidal regime and modest, albeit reduced, growth and survival at moderate salinities (5 and 10 ppt). For this reason, rapid detection and eradication of P. maculata in estuarine areas is needed to avoid the invasion of snails in these vital, productive environments.

Impact of an invasive predatory lizard on the endangered Hawaiian tree snail Achatinella mustelina: a threat assessment

All 41 species of the Hawaiian tree snail genus Achatinella were listed as endan- gered in the early 1980s, primarily due to predation by invasive species. Today, only 9 species are estimated to remain. The recent discovery of A. mustelina in gut contents of Jackson's chameleons Trioceros jacksonii xantholophus, a predatory arboreal African lizard introduced to Hawaii (USA) in 1972, was the first documentation of environmental impact by any reptile on native Hawaiian taxa. In this study, we assessed the predatory threat posed by chameleons to A. mustelina by (1) determining shell digestion and passage rates in daily fed and fasting individuals and (2) using these data to estimate time of ingestion of snails found in guts of field-collected chameleons. Our results indicate that daily food intake increases passage rate. Well fed chameleons passed largely intact A. mustelina shells in ~4 to 5 d, whereas starved individuals retained shells in their stomachs until complete digestion in ~8 d. Shell mass was digested at ~12.5% d �1 . In total, 8 A. mustelina were found in 45 field-collected lizards, and estimated time of ingestion, based on shell condition, was ~3 to 4 d prior to capture in all cases. Given a predator density of 45 per 2000 m 2 (0.5 acre) and assuming a feeding frequency of 8 snails every 3 to 4 d, we conservatively estimate that 45 chameleons could consume 730 to 974 snails yr �1 , per 2000 m 2 . Given the low growth and reproductive rates of Hawaiian tree snails, this level of impact is probably unsustain- able even over the short term, and immediate control action is warranted.

Effects of copper exposure on the energy metabolism in juveniles of the marine clam Mesodesma mactroides

In freshwater osmoregulating mollusks, Cu can cause toxicity by inducing ionoregulatory disturbances. In mussels, it inhibits the activity of key enzymes involved in Na+ uptake and consequently induces ionic and osmotic disturbances. In snails, Cu induces disruption of the Ca2+ homeostasis leading to effects in shell deposition and snail growth. However, the mechanisms involved in Cu toxicity in osmoconforming sweater mollusks remain unclear. Recent findings from our laboratory have suggested that Cu toxicity in marine invertebrates can be associated with both ionic and respiratory disturbances. In the present study, metabolic changes induced by waterborne Cu exposure were evaluated in the osmoconforming clam Mesodesma mactroides, a bivalve species widely distributed along the South American sandy beaches. Juvenile clams were kept under control conditions (no Cu addition in the water) or acutely (96h) exposed to Cu (96-h LC10=150μgL−1) in artificial seawater (30ppt). ATP, protein, lipid, glycogen and glucose contents were analyzed in gills, digestive gland, pedal muscle and hemolymph. Dinucleotide (NAD+ and NADH) content was also analyzed in gills, digestive gland and pedal muscle while pyruvate and lactate content was determined in pedal muscle and hemolymph. In all tissues analyzed, Cu exposure did not affect ATP content and NAD+/NADH ratio, except in the hemolymph, where a decrease in ATP content was observed. These findings indicate that clam cells, except those from hemolymph, were able to maintain a constant level of free energy. A significant increase in total protein content was observed in the digestive gland, which could be a compensatory mechanism to counteract the higher level of protein oxidation previously observed in M. mactroides exposed to Cu under the same experimental conditions. Finally, reduced glucose content in the pedal muscle paralleled by increased lactate content in the pedal muscle and hemolymph was observed in Cu-exposed clams. Overall, these findings indicate that Cu exposure is leading to an increased reliance upon the anaerobic energy production to maintain the overall cellular ATP production in the clam M. mactroides.

Effects of chronic waterborne nickel exposure on growth, ion homeostasis, acid-base balance, and nickel uptake in the freshwater pulmonate snail, Lymnaea stagnalis

The freshwater pulmonate snail, Lymnaea stagnalis, is the most sensitive aquatic organism tested to date for Ni. We undertook a series of experiments to investigate the underlying mechanism(s) for this observed hypersensitivity. Consistent with previous experiments, juvenile snail growth in a 21-day exposure was reduced by 48% relative to the control when exposed to 1.3μgl−1 Ni (EC20 less than the lowest concentration tested). Ca2+ homeostasis was significantly disrupted by Ni exposure as demonstrated by reductions in net Ca2+ uptake, and reductions in Ca2+ concentrations in the hemolymph and soft tissues. We also observed reduced soft tissue [Mg2+]. Snails underwent a significant alkalosis with hemolymph pH increasing from 8.1 to 8.3 and hemolymph TCO2 increasing from 19 to 22mM in control versus Ni-exposed snails, respectively. Unlike in previous studies with Co and Pb, snail feeding rates were found to be unaffected by Ni at the end of the exposure. Snails accumulated Ni in the soft tissue in a concentration-dependent manner, and Ni uptake experiments with 63Ni revealed a biphasic uptake profile – a saturable high affinity component at low exposure concentrations (36–189nM) and a linear component at the high exposure concentrations (189–1897nM). The high affinity transport system had an apparent Km of 89nM Ni2+ and Vmax of 2.4nmolg−1h−1. This equates to a logK of 7.1, significantly higher than logK's (2.6–5.2) for any other aquatic organisms evaluated to date, which will have implications for Biotic Ligand Model development. Finally, pharmacological inhibitors that block Ca2+ uptake pathways in snails did not inhibit Ni uptake, suggesting that the uptake of Ni does not occur via Ca2+ uptake pathways. As with Cu and Pb, the exact mechanism for the significant disruption in Ca2+ homeostasis and reduction in juvenile snail growth remains unknown.