Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses.

The exposure of animals to pollution in ecosystems is not always chronic. Toxicants can remain in aquatic ecosystems for a short-term. To improve the extrapolation of laboratory results to natural scenarios the inclusion of post-exposure periods is a relevant issue. The present study focuses on the assessment of cadmium toxicity on survival and behavior of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca) during exposure and post-exposure. Animals were exposed for 48 h to cadmium (0.05, 0.14, 0.44 and 1.34 mg Cd/L) and 168 h of post-exposure. During the post-exposure period an increase in mortality in all concentrations was observed. The effects observed during the post-exposure period on the LC50 and EC50 were significant. During the post-exposure, behavior showed a clear recovery in surviving animals exposed to 0.44 mg Cd/L. Animals exposed to 0.05 mg Cd/L did not show differences with control. Therefore, mortality after exposure should be included in the ecotoxicological bioassays for a more realistic estimation of the cadmium effects. To assess the degree of animal recovery after cadmium exposure, behaviour has been shown as an adequate parameter.

Peptidergic modulation of a multi-functional central pattern generator in the pulmonate snail.

Egg laying in pulmonate snails is a well-orchestrated process that involves a period of reduced locomotion, followed by substrate cleaning with rhythmic rasping of the surface to make tiny grooves, into which eggs are deposited. Although the neurohormonal control of initiating egg laying has been well established, the signals that modulate the buccal central pattern generator to substrate cleaning during egg laying are not known. Neuropeptides of the invertebrate gonadotropin-releasing hormone/corazonin family (invGnRH/CRZ) have been shown to be involved in reproduction and allied behaviors in many vertebrates and invertebrates. Here, we show that the buccal motor pattern underlying substrate cleaning during egg laying is altered by a vertebrate GnRH agonist. Signals from the intestinal nerve innervating reproductive structures, previously shown to be both necessary and sufficient for egg-laying behaviors, are blocked by a vertebrate GnRH antagonist. Further, the vertebrate GnRH-triggered response elicits rhythmic, phase 2 and non-phase 2 activity in the buccal motor pattern, with a shutdown of phase 3, indicative of repetitive rasping without accompanied swallowing behavior. Using immunohistochemistry, intracellular electrophysiology and extracellular nerve stimulation, we show that a member of the invGnRH/CRZ family of neuropeptides could be the signal that contextually switches the multifunctional buccal CPG to a biphasic rasping rhythm that underlies substrate cleaning behavior during egg laying in the pulmonate snail Planorbella (Helisoma) trivolvis.

Origin and significance of two pairs of head tentacles in the radiation of euthyneuran sea slugs and land snails.

The gastropod infraclass Euthyneura comprises at least 30,000 species of snails and slugs, including nudibranch sea slugs, sea hares and garden snails, that flourish in various environments on earth. A unique morphological feature of Euthyneura is the presence of two pairs of sensory head tentacles with different shapes and functions: the anterior labial tentacles and the posterior rhinophores or eyestalks. Here we combine molecular phylogenetic and microanatomical evidence that suggests the two pairs of head tentacles have originated by splitting of the original single tentacle pair (with two parallel nerve cords in each tentacle) as seen in many other gastropods. Minute deep-sea snails of Tjaernoeia and Parvaplustrum, which in our phylogeny belonged to the euthyneurans' sister group (new infraclass Mesoneura), have tentacles that are split along much of their lengths but associated nerves and epidermal sense organs are not as specialized as in Euthyneura. We suggest that further elaboration of cephalic sense organs in Euthyneura closely coincided with their ecological radiation and drastic modification of body plans. The monotypic family Parvaplustridae nov., superfamily Tjaernoeioidea nov. (Tjaernoeiidae + Parvaplustridae), and new major clade Tetratentaculata nov. (Mesoneura nov. + Euthyneura) are also proposed based on their phylogenetic relationships and shared morphological traits.

Mechanism behind the neuronal ephaptic coupling during synchronizing by specific brain-triggered wave as neuronal motor toolkit.

Probable mechanism behind the neuronal ephaptic coupling is investigated based on the introduction of "Brain"-triggered potential excitation signal smartly with a specific very low frequency (VLF) waves as a neuronal motor toolkit. Detection of this electric motor toolkit is attributed to in-vitro precise analyses of a neural network of snail, along to the disconnected snail's neuronal network as a control. This is achieved via rapid (real-time) electrical signals acquisition by blind patch-clamp method during micro-electrode implanting in the neurons at the gigaseal conditions by the surgery operations. This process is based on its waveform (potential excitation signal) detection by mathematical curve fitting process. The characterized waveform of this electrical signal is "Saw Tooth" that is smartly stimulated, alternatively, by the brain during triggering the action potential's (AP's) hyperpolarization zone at a certain time interval at the several µs levels. Triggering the neuron cells results in (1) observing a positive shift (10.0%, depending on the intensity of the triggering wave), and (2) major promotion in the electrical current from sub nano (n) to micro (µ) amper (nA, µA) levels. Direct tracing the time domain (i.e., electrical signal vs. time) and estimation of the frequency domain (diagram of electrical response vs. the applied electrical frequencies) by the "Discrete Fast Fourier Transform" algorithm approve the presence of bilateral and reversible electrical currents between axon and dendrite. This mechanism therefore opens a novel view about the neuronal motor toolkit mechanism, versus the general knowledge about the unilateral electrical current flow from axon to dendrite operations in as neural network. The reliability of this mechanism is evaluated via (1) sequential modulation and demodulation of the snail's neuron network by a simulation electrical functions and sequentially evaluation of the neuronal current sensitivity between pA and nA (during the promotion of the signal-to-noise ratio, via averaging of 30 ± 1 (n = 15) and recycling the electrical cycles before any neuronal response); and (2) operation of the process on the differentiated stem cells. The interstice behavior is attributed to the effective role of Ca2+ channels (besides Na+ and K+ ionic pumping), during hyper/hypo calcium processes, evidenced by inductively coupled plasma as the selected analytical method. This phenomenon is also modeled during proposing quadrupole well potential levels in the neuron systems. This mechanism therefore points to the microprocessor behavior of neuron networks. Stimulation of the neuronal system based on this mechanism, not only controls the sensitivity of neuron electrical stimulation, but also would open a light window for more efficient operating the neuronal connectivity during providing interruptions by phenomena such as neurolysis as well as an efficient treatment of neuron-based disorders.

[Comprehensive benefits of agroforestry snail control forests in Eryuan County, Yunnan Province].

OBJECTIVE: To investigate the efficiency of various agroforestry systems for snail control in plateau hilly schistosomiasis-endemic areas of Yunnan Province, so as to provide insights into the construction of agroforestry schistosomiasis control projects in plateau hilly regions. METHODS: The pilot areas of snail control forests with various agroforestry systems were built in snail-breeding farmlands in Eryuan County, Yunnan Province in 2010, and the economic benefits and snail control effect were investigated in 2018. In addition, a fuzzy comprehensive evaluation model was created to screen the agroforestry system with high comprehensive benefits. RESULTS: A total of 14 types of pilot areas of snail control forests with various agroforestry systems were built. Economic benefit analysis showed that the"walnut + garlic"pattern had the best economic benefit, with annual economic benefits of 270 000 Yuan/hm2, followed by the"walnut + chili"pattern (annual economic benefits of 120 000 Yuan/hm2) and the "walnut + vegetables"pattern (annual economic benefits of 105 000 Yuan/hm2). No snails were detected in 8 types of the agroforestry systems, including the"walnut + chili"pattern, the"walnut + tobacco"pattern and the"walnut + garlic"pattern; however, there were snail found with various densities in other types of systems. Fuzzy comprehensive evaluation showed that the"walnut + garlic"pattern had the best comprehensive control effect, followed by the"walnut + chili"pattern and the"walnut + tobacco" pattern, while the pure grassland pattern showed no effect on snail control. CONCLUSIONS: The agroforestry system is a preferential approach of forestry schistosomiasis control in plateau hilly schistosomiasis-endemic areas, which not only achieves snail control effects, but also promotes economic development and ecological construction in poor hilly areas.

Phenotypic Variation in Mitochondria-Related Performance Traits Across New Zealand Snail Populations.

Mitochondrial function is critical for energy homeostasis and should shape how genetic variation in metabolism is transmitted through levels of biological organization to generate stability in organismal performance. Mitochondrial function is encoded by genes in two distinct and separately inherited genomes-the mitochondrial genome and the nuclear genome-and selection is expected to maintain functional mito-nuclear interactions. The documented high levels of polymorphism in genes involved in these mito-nuclear interactions and wide variation for mitochondrial function demands an explanation for how and why variability in such a fundamental trait is maintained. Potamopyrgus antipodarum is a New Zealand freshwater snail with coexisting sexual and asexual individuals and, accordingly, contrasting systems of separate vs. co-inheritance of nuclear and mitochondrial genomes. As such, this snail provides a powerful means to dissect the evolutionary and functional consequences of mito-nuclear variation. The lakes inhabited by P. antipodarum span wide environmental gradients, with substantial across-lake genetic structure and mito-nuclear discordance. This situation allows us to use comparisons across reproductive modes and lakes to partition variation in cellular respiration across genetic and environmental axes. Here, we integrated cellular, physiological, and behavioral approaches to quantify variation in mitochondrial function across a diverse set of wild P. antipodarum lineages. We found extensive across-lake variation in organismal oxygen consumption and behavioral response to heat stress and differences across sexes in mitochondrial membrane potential but few global effects of reproductive mode. Taken together, our data set the stage for applying this important model system for sexual reproduction and polyploidy to dissecting the complex relationships between mito-nuclear variation, performance, plasticity, and fitness in natural populations.

The making of natural iron sulfide nanoparticles in a hot vent snail.

Biomineralization in animals exclusively features oxygen-based minerals with a single exception of the scaly-foot gastropod Chrysomallon squamiferum, the only metazoan with an iron sulfide skeleton. This unique snail inhabits deep-sea hot vents and possesses scales infused with iron sulfide nanoparticles, including pyrite, giving it a characteristic metallic black sheen. Since the scaly-foot is capable of making iron sulfide nanoparticles in its natural habitat at a relatively low temperature (∼15 °C) and in a chemically dynamic vent environment, elucidating its biomineralization pathways is expected to have significant industrial applications for the production of metal chalcogenide nanoparticles. Nevertheless, this biomineralization has remained a mystery for decades since the snail's discovery, except that it requires the environment to be rich in iron, with a white population lacking in iron sulfide known from a naturally iron-poor locality. Here, we reveal a biologically controlled mineralization mechanism employed by the scaly-foot snail to achieve this nanoparticle biomineralization, through δ34 S measurements and detailed electron-microscopic investigations of both natural scales and scales from the white population artificially incubated in an iron-rich environment. We show that the scaly-foot snail mediates biomineralization in its scales by supplying sulfur through channel-like columns in which reaction with iron ions diffusing inward from the surrounding vent fluid mineralizes iron sulfides.

Protists and other organisms on a minute snail periostracum / Protistas e outros organismos em um pequeno periostracum de caracol

Abstract Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.

Resumo Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.

Phylogenetics and species delimitations of the operculated land snail Cyclophorus volvulus (Gastropoda: Cyclophoridae) reveal cryptic diversity and new species in Thailand.

Recent conceptual and practical advances in phylogenetic species delimitation have enabled progressively robust biodiversity studies. Delimiting species in widespread taxa is an intriguing problem; the edible operculated land snail Cyclophorus volvulus (Müller, 1774) is a good example since it shows a high degree of shell and color variation along with a widespread distribution throughout Thailand. Taxonomic boundaries for C. volvulus were examined and clarified using a combined morphological and phylogenetic approach, the latter of which was based on both nuclear and mitochondrial gene sequences. Moreover, three species delimitation analyses were applied: Poisson tree processes (PTP), automatic barcode gap discovery (ABGD), and generalized mixed Yule-coalescent (GMYC). All phylogenetic trees revealed that C. volvulus was polyphyletic and comprised of three clades that coincided with their geographic distribution. The three species delimitation analyses concurred with the phylogenies and formed at least three groups. According to the results, C. volvulus s.l., as currently recognized, consists of three distinct species in Thailand: C. volvulus s.s., C. occultus sp. nov., and C. borealis sp. nov., which are described herein. Moreover, several of these highly distinct C. volvulus evolutionarily significant units (ESU) are likely to require urgent conservation attention.

Uptake and adverse effects of polyethylene terephthalate microplastics fibers on terrestrial snails (Achatina fulica) after soil exposure.

Recent studies have demonstrated the occurrence of microplastic fibers (MFs) in soil environments. To determine whether MFs are harmful for soil biota, we evaluated toxic effects on terrestrial snails (Achatina fulica) after 28 d exposure to polyethylene terephthalate MFs at concentrations of 0.01-0.71 g kg-1 (dry soil weight). Digestion kinetics experiments on 24 snails showed that MFs can be ingested and excreted within 48 h. We found the appearance of cracks and deterioration on the surface of MFs after depuration by the digestive system. Prolonged exposure to 40 snails showed that 0.14-0.71 g kg-1 MFs caused an average reduction of 24.7-34.9% food intake and 46.6-69.7% excretion. 0.71 g kg-1 MFs induced significant villi damage in the gastrointestinal walls of 40% snails, but did not influence the histology of the liver and kidney. Moreover, 0.71 g kg-1 MFs exposure reduced glutathione peroxidase (59.3 ±â€¯13.8%) and total antioxidant capacity (36.7 ±â€¯8.5%), but elevated malondialdehyde level (58.0 ±â€¯6.4%) in the liver, which indicates oxidative stress is involved in the toxic mechanism. Our results suggest that MFs have adverse impacts on the fitness of soil organisms, and highlight the ecological risks of microplastic pollution in terrestrial ecosystems.

Ecotoxicological biomarkers as investigating tools to evaluate the impact of acrylamide on Theba pisana snails.

Acrylamide (ACR) is a widespread industrial chemical with recognized adverse effects not only to humans but to other organisms in the environment as well. In the present study, the ecotoxicological effects of dietary exposure to sublethal concentration (1/20 LC50) of ACR on the land snail, Theba pisana after 2 weeks of exposure and 1-week recovery with respect to oxidative stress parameters; lipid peroxidation (LPO), reduced glutathione (GSH), catalase (CAT), and glutathione-S-transferase (GST), cytogenetic parameter; deoxyribonucleic acid (DNA) content, as well as immunological parameters; cell death, phagocytosis, lysosomal membrane stability (LMS), lectins, superoxide anion (O2-) generation, phenoloxidase (PO), peroxidase (POD), and hemocyanin (Hc) were examined. The results showed that ACR significantly increased LPO level and the activity of CAT and GST, cell death, and Hc level, whereas a significant decline in DNA and GSH contents, phagocytic activity, LMS, lectins, O2- generation, POD, and PO activities compared to the controls after 2-week exposure was observed. After 1-week recovery, most of the tested parameters in exposed snails were permanent and not reversible to the control levels. This study suggests that the tested multiple parameters of T. pisana species may be used as biomarkers of ACR exposure. Besides, T. pisana snails could be used as a good sentinel organism for ACR exposure in pollution monitoring studies.

Biochemical and molecular alterations in freshwater mollusks as biomarkers for petroleum product, domestic heating oil.

To investigate the effect one of the oil products, domestic heating oil (DHO), on freshwater mollusks, Unio tigridis and Viviparous bengalensis were exposed to three DHO concentrations for each species (5.8, 8.7, and 17.4 ml L-1 for mussels; 6.5, 9.7, and 19.5 mlL-1 for snails, respectively). Antioxidant enzymes (superoxide dismutase, catalase), malondialdehyde, acetylcholinesterase and DNA damage in both species tissues were monitored over 21 days. The results showed that both antioxidant enzymes concentration (SOD and CAT) increased in the lowest DHO concentrations (5.8, and 8.7 ml L-1), and then decreased in the highest concentration (17.4 ml L-1) as the same pattern for Unio tigridis, but this not occurred for Viviparous bengalensis. MDA values recorded significantly increased compared to control. No reduction was observed in AChE concentrations in soft tissues of both mollusks may due to that DHO was a non-neurotoxicant to Unio tigridis and Viviparous bengalensis. The results of DNA damage parameters were showed significant differences (p≤ 0.05) between control and DHO concentrations except lowest concentration for each parameter measured in digestive gland of Unio tigridis. As well as, these significant differences were recorded between control and three concentrations of DHO exposure for comet length, and tail length parameters, and between control and highest oil concentration for tail moment in Viviparous bengalensis. DHO has the ability to prevent the reproduction of Viviparous bengalensis snail relation to control, that is what we considered strong evidence of the toxicity properties of DHO on the reproductive status of this species of snails. SOD, CAT, and MDA were useful biomarkers for evaluating the toxicity of DHO in mussel and snails, and comet assay was a good tool to assess the potential genotoxicity of DHO.

Predation scars may influence host susceptibility to pathogens: evaluating the role of corallivores as vectors of coral disease.

Infectious diseases not regulated by host density, such as vector-borne diseases, have the potential to drive population declines and extinctions. Here we test the vector potential of the snail Drupella sp. and butterflyfish Chaetodon plebeius for two coral diseases, black band (BBD) and brown band (BrB) disease. Drupella transmitted BrB to healthy corals in 40% of cases immediately following feeding on infected corals, and even in 12% of cases 12 and 24 hours following feeding. However, Drupella was unable to transmit BBD in either transmission treatment. In a field experiment testing the vector potential of naturally-occurring fish assemblages, equivalent numbers of caged and uncaged coral fragments became infected with either BrB, BBD or skeletal eroding band, indicating that corallivorous fish were unlikely to have caused transmission. In aquaria, C. plebeius did not transmit either BBD or BrB, even following extended feeding on both infected and healthy nubbins. A literature review confirmed only four known coral disease vectors, all invertebrates, corroborating our conclusion that polyp-feeding fishes are unlikely to be vectors of coral diseases. This potentially because polyp-feeding fishes produce shallow lesions, not allowing pathogens to invade coral tissues. In contrast, corallivorous invertebrates that create deeper feeding scars increase pathogens transmission.

Cigarette butts may have low toxicity to soil-dwelling invertebrates: Evidence from a land snail.

Cigarette butts are a common form of litter that is often deposited on soil, where toxins from butts may affect soil-dwelling organisms. We examined possible toxicity of cigarette butts to the woodland snail Anguispira alternata using a toxicity study with cigarette butt effluent and a lab-based habitat choice experiment in which snails could feed or rest on areas with different butt densities. No mortality occurred during the 32-day toxicity study, which used six effluent concentrations ranging from 0 to 4butts/l (0 to 0.92butts/kg of soil). Neither food consumption nor snail growth differed among the effluent concentrations. When provided a choice among four habitats with 0 to 4 cigarette butts, snails selected to preferentially rest in the 0-butt habitat and avoided the 4-butt habitat. This distribution pattern was strong during the first wk. but became weaker over time and largely disappeared by the end of the 3-wk experiment. Snails did not discriminate among butt densities when feeding. This is the first toxicity test using cigarette butts on soil-dwelling invertebrates. Declining aversion to cigarette butts over a 3-wk period may indicate declining toxicity of terrestrially deposited butts as they age, but further testing is needed.

Corallivory and the microbial debacle in two branching scleractinians.

The grazing activity by specific marine organisms represents a growing threat to the survival of many scleractinian species. For example, the recent proliferation of the corallivorous gastropod Drupella now constitutes a critical case in all South-East Asian waters. If the damaging effects caused by this marine snail on coral polyps are relatively well known, the indirect incidence of predation on coral microbial associates is still obscure and might also potentially impair coral health. In this study, we compared the main ecological traits of coral-associated bacterial and viral communities living in the mucus layer of Acropora formosa and Acropora millepora, of healthy and predated individuals (i.e., colonized by Drupella rugosa), in the Bay of Van Phong (Vietnam). Our results show a substantial impact of the gastropod on a variety of microbiological markers. Colonized corals harbored much more abundant and active epibiotic bacteria whose community composition shifted toward more pathogenic taxa (belonging to the Vibrionales, Clostridiales, Campylobacterales, and Alteromonadales orders), together with their specific phages. Viral epibionts were also greatly influenced by Drupella corallivory with spectacular modifications in their concentrations, life strategies, genotype richness, and diversity. Novel and abundant circular Rep-encoding ssDNA viruses (CRESS-DNA viruses) were detected and characterized in grazed corals and we propose that their occurrence may serve as indicator of the coral health status. Finally, our results reveal that corallivory can cause severe dysbiosis by altering virus-bacteria interactions in the mucus layer, and ultimately favoring the development of local opportunistic infections.

Feeding Behavior of an Aquatic Snail as a Simple Endpoint to Assess the Exposure to Cadmium.

One of the aims of ecotoxicology is the assessment of the effects of chemicals on the ecosystems. Bioassays assessing lethality are frequently used in ecotoxicology, however they usually employ supra-environmental toxic concentrations. Toxicity tests employing behavioral endpoints may present a balance between simplicity (i.e., laboratory bioassays) and complexity (i.e., relevant ecological effects). The aim of this study was to develop a feeding behavioral bioassay with the aquatic snail, Potamopyrgus antipodarum, which included a 2 days exposure to cadmium, followed by a 9 days post-exposure observational period. Several behavioral feeding endpoints were monitored, including percentage of actively feeding animals, percentage of animals in food quadrants and a mobility index. The percentage of actively feeding animals was reduced by the four cadmium treatments (0.009, 0.026, 0.091 and 0.230 mg Cd/L) with the stronger effect in the highest concentration. The two highest cadmium concentrations significantly reduced the percentage of animals in food quadrants and the mobility index. Therefore, the percentage of actively feeding animals was the most sensitive endpoint to cadmium toxicity as the four cadmium concentrations caused a significant decrease in this endpoint. It is concluded that feeding behavior is a useful endpoint to detect the exposure of aquatic snails to cadmium.

Stenotrophomonas-Like Bacteria Are Widespread Symbionts in Cone Snail Venom Ducts.

Cone snails are biomedically important sources of peptide drugs, but it is not known whether snail-associated bacteria affect venom chemistry. To begin to answer this question, we performed 16S rRNA gene amplicon sequencing of eight cone snail species, comparing their microbiomes with each other and with those from a variety of other marine invertebrates. We show that the cone snail microbiome is distinct from those in other marine invertebrates and conserved in specimens from around the world, including the Philippines, Guam, California, and Florida. We found that all venom ducts examined contain diverse 16S rRNA gene sequences bearing closest similarity to Stenotrophomonas bacteria. These sequences represent specific symbionts that live in the lumen of the venom duct, where bioactive venom peptides are synthesized.IMPORTANCE In animals, symbiotic bacteria contribute critically to metabolism. Cone snails are renowned for the production of venoms that are used as medicines and as probes for biological study. In principle, symbiotic bacterial metabolism could either degrade or synthesize active venom components, and previous publications show that bacteria do indeed contribute small molecules to some venoms. Therefore, understanding symbiosis in cone snails will contribute to further drug discovery efforts. Here, we describe an unexpected, specific symbiosis between bacteria and cone snails from around the world.

Evaluation of the feeding preference between the aquatic macrophytes Egeria densa and Chara indica by the invasive mollusk Melanoides tuberculata / Avaliação da preferência do molusco invasor Melanoides tuberculata pelas macrófitas aquáticas Egeria densa e Chara indica

Abstract This study evaluated the feeding preference of the invasive mollusk Melaniudes tuberculata between the aquatic macrophytes Egeria densa and Chara indica. The experiment consisted of twelve experimental units (glass aquariums) each of which contained three liters of water and three compartments. Fragments of E. densa and C. indica were placed in separate compartments within each unit; the third compartment, which did not contain macrophytes, was used as the control. Twenty Melanoides tuberculata individuals were placed in each unit and monitored hourly over the course of 24 hours for preferential movements. Physical and chemical water variables were measured at the beginning and end of the experiment. Habitat complexity was determined through collected macrophyte fragments and determined using the Fractop program. After 24 hours, the highest average number of individuals was observed in the treatment with Chara indica (ten individuals), which differed significantly from the treatment with E. densa (four individuals) and the control treatment (two individuals). The number of individuals between the E. densa and control treatment were similar. M. tuberculata showed a clear feeding preference for C. indica.

Resumo O presente trabalho teve como objetivo avaliar a preferência do molusco invasor M. tuberculata pelas macrófitas aquáticas Egeria densa e Chara indica. Doze unidades experimentais (aquários de vidro), com dimensões de 30×15×15 cm, subdivida em três compartimentos foram utilizadas. Em cada unidade experimental foram adicionados três litros de água, sendo que em dois compartimentos foram adicionados aleatoriamente fragmentos de E. densa e C. indica e um compartimento ficou sem planta (controle). Na parte central do aquário foram adicionados os moluscos equidistantes dos três compartimentos. O experimento teve duração de 24 horas, sendo vistoriado e contabilizado o número de organismos presentes em cada compartimento a cada hora. As variáveis ambientais foram medidas no inicio e fim do experimento. Fragmentos de macrófitas foram coletados para determinação da complexidade do habitat através do programa Fractop. Após 24 horas, os resultados mostraram um maior valor médio de indivíduos no tratamento que possuía Chara indica (dez indivíduos), que diferiu significativamente do tratamento com E. densa (quatro indivíduos) e do tratamento controle (dois indivíduos). Os tratamentos com E. densa e o controle foram semelhantes entre si evidenciando, uma possível preferência do molusco por a C. indica.

Abundance of the reef-building Petaloconchus varians (Gastropoda: Vermetidae) on intertidal rocky shores at Ilha Grande Bay, southeastern Brazil

ABSTRACT The reef-building vermetid Petaloconchus varians occurs in the western Atlantic Ocean, from the Caribbean Sea to the southern coast of Brazil. The present study evaluated the abundance of P. varians on intertidal rocky shores in Ilha Grande Bay (Rio de Janeiro State), and characterized their reefs, describing the species density, besides the weight and the belt width of the reefs. Petaloconchus varians reefs were recorded at 25 sites, with rocky shores exposed to different wave action (very sheltered, sheltered, semi-exposed and exposed) and slopes (10° to 46°). Clusters of individuals constructed large reefs along the middle intertidal zone, creating a wide belt (38 cm to 2 m). The density of P. varians and the weight of the reefs ranged from 620 to 2,559 ind.100 cm-2 and from 100 to 1,500 g.100 cm-2, respectively. Considering that the species was last reported from the area in the mid-20th century, the present study suggests that P. varians reefs are becoming dominant in the intertidal zone of rocky shores in Ilha Grande Bay. This is a contribution to knowledge of this ecosystem in Ilha Grande Bay, in view of local or global ecological changes.