Compensatory shell thickening in corrosive environments varies between related rocky-shore and estuarine gastropods

Few studies have considered the capabilities of gastropods living in minerally-deficient acidified coastal waters to compensate for outer shell corrosion or compromised growing edge shell production. We compared inner shell thickening between pristine shells (control) and corroded shells (experiment) of two related intertidal neritid gastropod species from reduced salinity and acidified environments. We predicted that the rocky-shore, Nerita chamaeleon, which has greater access to shell building biomineralization substrates, should better control shell thickness than the estuarine, Neripteron violaceum. Accordingly, N. chameleon was found to compensate perfectly for variation in the thickness of the outer calcitic blocky layer (BL). Optimal shell thickness (OST) was maintained by selective reabsorption of the aperture ridge of the distal shell (aragonitic crossed-lamellar layer, CL) and by increased internal deposition of proximal (older) shell (aragonitic protocrossed lamellar, PCL). Despite greater exposure to acidification and hyposalinity, N. violaceum showed no significant compensatory shell thickening. These findings reveal that shell thickening capability may vary greatly among intertidal gastropods and that this may be constrained by environmental biomineralization substrate availability. Such environmentally-related responses carry implications for predicted future reductions in coastal water pH and salinity.

Effects of microplastics and nanoplastics on host-parasite interactions in aquatic environments

Microplastics (MPs) and nanoplastics (NPs) are now widely recognized as a ubiquitous and pervasive environmental pollutant with important consequences for aquatic fauna in particular; however, little is known regarding their potential effects on interactions between hosts and their parasites or pathogens. We conducted a literature survey of published studies that have conducted empirical investigations of MP and NP influences on infectious disease dynamics to summarize the current state of knowledge. In addition, we examined the effects of microbead (MB) ingestion on the longevity of freshwater snails (Stagnicola elodes) infected by the trematode Plagiorchis sp., along with their production of infectious stages (cercariae), with a 3-week lab study during which snails were fed food cubes containing either 0, 10 or 100 polyethylene MBs sized 106-125 μm. We found 22 studies that considered MP and NP influences on host resistance or tolerance-20 of these focused on aquatic systems, but there was no clear pattern in terms of host effects. In our lab study, MB diet had marginal or few effects on snail growth and mortality, but snails exhibited a significant non-monotonic response with respect to cercariae production as this was greatest in those fed the high-MB diet. Both our literature summary and experimental study indicate that MPs and NPs can have complex and unpredictable effects on infectious disease dynamics, with an urgent need for more investigations that examine how plastics can affect aquatic fauna through direct and indirect means.

Understanding the differential impacts of two antidepressants on locomotion of freshwater snails (Lymnaea stagnalis)

There is growing evidence of negative impacts of antidepressants on behavior of aquatic non-target organisms. Accurate environmental risk assessment requires an understanding of whether antidepressants with similar modes of action have consistent negative impacts. Here, we tested the effect of acute exposure to two antidepressants, fluoxetine and venlafaxine (0-50 µg/L), on the behavior of non-target organism, i.e., freshwater pond snail, Lymnaea stagnalis. As compounds interact with chemical cues in the aquatic ecosystems, we also tested whether the effects altered in the presence of bile extract containing 5α-cyprinol sulfate (5α-CPS), a characterized kairomone of a natural predator, common carp (Cyprinus carpio). Behavior was studied using automated tracking and analysis of various locomotion parameters of L. stagnalis. Our results suggest that there are differences in the effects on locomotion upon exposure to venlafaxine and fluoxetine. We found strong evidence for a non-monotonic dose response on venlafaxine exposure, whereas fluoxetine only showed weak evidence of altered locomotion for a specific concentration. Combined exposure to compounds and 5α-CPS reduced the intensity of effects observed in the absence of 5α-CPS, possibly due to reduced bioavailability of the compounds. The results highlight the need for acknowledging different mechanisms of action among antidepressants while investigating their environmental risks. In addition, our results underline the importance of reporting non-significant effects and acknowledging individual variation in behavior for environmental risk assessment.

Expression dynamics of the aplysia abyssovirus

Two recent studies documented the genome of a novel, extremely large (35.9 kb), nidovirus in RNA sequence databases from the marine neural model Aplysia californica. The goal of the present study was to document the distribution and transcriptional dynamics of this virus, Aplysia abyssovirus 1 (AAbV), in maricultured and wild animals. We confirmed previous findings that AAbV RNA is widespread and reaches extraordinary levels in apparently healthy animals. Transmission electron microscopy identified viral replication factories in ciliated gill epithelial cells but not in neurons where viral RNA is most highly expressed. Viral transcripts do not exhibit evidence of discontinuous RNA synthesis as in coronaviruses but are consistent with production of a single leaderless subgenomic RNA, as in the Gill-associated virus of Penaeus monodon. Splicing patterns in chronically infected adults suggested high levels of defective genomes, possibly explaining the lack of obvious disease signs in high viral load animals.

Anthropogenic nitrogen pollution inferred by stable isotope records of crustose coralline algae

Since reef ecosystems can offer intricate habitats for various marine organisms, calcified reefs may contain valuable long-term environmental data. This study investigated stable isotopic composition of marine organisms from the Taoyuan and Linshanbi crustose coralline algae (CCA) reef ecosystems to understand sewage pollution. CCA samples from Taoyuan (Palaeo Xin A: ∼1000 years old and Palaeo G: ∼7000 years old) and Linshanbi (Palaeo L: ∼7000 years old and modern CCA) had significantly lower δ15N values (2.5-5.6 ‰) compared to modern CCA from Taoyuan (10.2 ± 1.2 ‰). Intertidal organisms from the Taoyuan CCA reef also showed higher δ15N values than those from Linshanbi CCA reef, indicating anthropogenic stress in both ecosystems. Long-term pollution monitoring and effective strategies to mitigate sewage pollution are recommended for these CCA reef ecosystems.

Core gut microbes Cloacibacterium and Aeromonas associated with different gastropod species could be persistently transmitted across multiple generations

BACKGROUND

Studies on the gut microbiota of animals have largely focused on vertebrates. The transmission modes of commensal intestinal bacteria in mammals have been well studied. However, in gastropods, the relationship between gut microbiota and hosts is still poorly understood. To gain a better understanding of the composition of gut microbes and their transmission routes in gastropods, a large-scale and long-term experiment on the dynamics and transmission modes of gut microbiota was conducted on freshwater snails.

RESULTS

We analyzed 244 microbial samples from the digestive tracts of freshwater gastropods and identified Proteobacteria and Bacteroidetes as dominant gut microbes. Aeromonas, Cloacibacterium, and Cetobacterium were identified as core microbes in the guts, accounting for over 50% of the total sequences. Furthermore, both core bacteria Aeromonas and Cloacibacterium, were shared among 7 gastropod species and played an important role in determining the gut microbial community types of both wild and cultured gastropods. Analysis of the gut microbiota at the population level, including wild gastropods and their offspring, indicated that a proportion of gut microbes could be consistently vertically transmitted inheritance, while the majority of the gut microbes resulted from horizontal transmission. Comparing cultured snails to their wild counterparts, we observed an increasing trend in the proportion of shared microbes and a decreasing trend in the number of unique microbes among wild gastropods and their offspring reared in a cultured environment. Core gut microbes, Aeromonas and Cloacibacterium, remained persistent and dispersed from wild snails to their offspring across multiple generations. Interestingly, under cultured environments, the gut microbiota in wild gastropods could only be maintained for up to 2 generations before converging with that of cultured snails. The difference observed in gut bacterial metabolism functions was associated with this transition. Our study also demonstrated that the gut microbial compositions in gastropods are influenced by developmental stages and revealed the presence of Aeromonas and Cloacibacterium throughout the life cycle in gastropods. Based on the dynamics of core gut microbes, it may be possible to predict the health status of gastropods during their adaptation to new environments. Additionally, gut microbial metabolic functions were found to be associated with the adaptive evolution of gastropods from wild to cultured environments.

CONCLUSIONS

Our findings provide novel insights into the dynamic processes of gut microbiota colonization in gastropod mollusks and unveil the modes of microbial transmission within their guts. Video Abstract.

First record of microplastic in the Brazilian sea hare Aplysia brasiliana Rang, 1828 (Mollusca: Aplysiidae)

The presence of plastic debris in the marine environment has reached massive levels in the past decades. In marine environments, microplastics can exist for hundreds of years and the presence of microplastics in this environment has been reported since 1970 and since then has been considered ubiquitous. Mollusks are being used as microplastic pollution indicators, especially in coastal areas and bivalves are more often used in microplastic-monitoring studies. On the other hand, gastropods are poorly used as indicators for microplastic pollution, even though they are the most diverse group of mollusks. The sea hares of the genus Aplysia are herbivorous gastropods, important model organisms commonly used in neuroscience studies, isolating the compounds in their defensive ink. Until today, there is no previous record of the presence of MPs in Aplysia gastropods. Therefore, this study aims to investigate the presence of microplastics in tissues of A. brasiliana found in southeastern Brazil. We collected seven individuals of A. brasiliana from a beach in southeastern Brazil, dissected them to isolate the digestive tract and the gills, and digested the tissues with a solution of 10 % NaOH. In the end, 1021 microplastic particles were found, 940 in the digestive tissue, and 81 in the gills. These results represent the first record of the presence of microplastics in the Brazilian sea hare A. brasiliana.

Physiological and biochemical responses of the estuarine pulmonate mud snail, Amphibola crenata, sub-chronically exposed to waterborne cadmium

Physiological and biochemical responses of the pulmonate mud snail, Amphibola crenata, to waterborne cadmium (Cd) were investigated to determine the mechanisms of toxicity and impacts of a 21-d Cd exposure. Mud snails were exposed to nominal Cd concentrations of 0, 0.2, 4 and 8 mg L ^- 1 and bioaccumulation, whole animal physiological (oxygen consumption, ammonia excretion and oxygen:nitrogen), and tissue level biochemical (catalase activity, lipid peroxidation, glycogen, glucose and protein) endpoints were measured every 7 days. At the two highest Cd exposure concentrations complete mortality was observed over 21-d. In surviving animals, oxygen consumption declined and ammonia excretion rate increased with Cd exposure concentration and duration. The increased ammonia excretion likely reflected enhanced protein metabolism as suggested by a reduced oxygen:nitrogen (O:N). Increasing waterborne Cd concentration and exposure time led to increasing metal accumulation in all tissues. The snail viscera showed the highest Cd accumulation. Both catalase activity and lipid peroxidation in the viscera significantly increased with Cd exposure concentration and time, whereas, the foot muscle and remaining tissues (kidney, mantle, remaining digestive tissues and heart) showed increased catalase activity and lipid peroxidation at higher Cd concentrations (4 and 8 mg L ^- 1), suggestive of an effect of Cd on oxidative stress. Over the course of 21 days, Cd exposure resulted in significantly lower levels of glycogen in viscera relative to Cd-free controls, reflecting an increased energy demand. Haemolymph glucose rose initially and then fell with increased exposure duration, while haemolymph protein generally exhibited an increased concentration in Cd-exposure groups, reflecting the changes in energy substrates noted for somatic tissues. These results suggest that the physiological and biochemical responses of A. crenata to Cd are conserved relative to other aquatic animals, and were tissue-specific, dose- and time-dependant.

The population structure, sex ratio and reproductive potential of limpets (Patella spp.) on natural shores and artificial structures in the Irish Sea

Artificial structures often support depauperate communities compared to natural rocky shores. Understanding variation in ecological success across shore types, particularly regarding habitat-forming species or those with structuring roles, is important to determine how artificial structure proliferation may influence ecosystem functioning and services. We investigated the population structure, sex ratio and reproductive potential of limpets on natural shores and artificial structures on Irish Sea coasts. Limpets were generally less abundant and Patella vulgata populations were often male dominated on artificial structures compared to natural shores, suggesting that shore type may influence these factors. P. vulgata length varied across sites within the Irish Sea (nested in coast and shore type) in autumn/winter, as well as temporally across sites along the Welsh coast. There was no difference in the proportion of P. vulgata in advanced stages of gonad development across shore types. The results suggest that rip-rap artificial structures may provide a habitat comparable to natural shores, however, the addition of ecological engineering interventions on artificial structures may allow limpet populations to better approximate those on natural shores.

Textile microfibers in wild Antarctic whelk Neobuccinum eatoni (Smith, 1875) from Terra Nova Bay (Ross Sea, Antarctica)

Antarctica has been affected directly and indirectly by human pressure for more than two centuries and recently plastic pollution has been recognized as a further potential threat for its unique biodiversity. Global long-range transport as well as local input from anthropogenic activities are potential sources of plastic pollution in both terrestrial and marine Antarctic territories. The present study evaluated the presence of microplastics in specimens of the Antarctic whelk Neobuccinum eatoni, a key species in benthic communities of the Ross Sea, one of the largest marine protected areas worldwide. To this aim, a thermo-oxidative extraction method was applied for microplastic isolation and quantification, and polymer identification was performed by manual μ-FTIR spectroscopy. Textile (semi-)synthetic or composite microfibers (length range: 0.8-5.7 mm) were found in 27.3% of whelk specimens, suggesting a low risk of bioaccumulation along Antarctic benthic food webs in the Ross Sea. Their polymer composition (of polyethylene terephthalate and cellulose-polyamide composites) matched those of outdoor technical clothing in use by the personnel of the Italian "Mario Zucchelli" station near Terra Nova Bay in the Ross Sea. Such findings indicate that sewage from base stations may act as potential local sources of textile microplastic fibers in this remote environment. More in-depth monitoring studies aiming at defining the extent of microplastic contamination related to such sources in Antarctica are encouraged.

A case study on small-size microplastics in water and snails in an urban river

Microplastic pollution has become pervasive in aquatic ecosystems. They readily interact with aquatic biota, potentially subjecting them to ecological and health risks. Urban rivers are also affected by microplastics due to intense anthropogenic activity. Nevertheless, relatively little is known about the physiocochemistry or ecotoxicology of microplastics in urban rivers. The present study used laser direct infrared chemical imaging to investigate microplastic pollution in a highly urbanized river in Beijing, China. Surface water was sampled at five sites along the river in March and July, and the benthic snail Bellamya aeruginosa was also collected at each location in July. Thirteen and fifteen different polymers were detected and identified in the surface water sampled in March and July, respectively. Thirteen different polymers were found and isolated in the snails. Of these, polypropylene, polyamide and polyethylene predominated in the microplastic particles. Moreover, the average abundance of the microplastic was significantly higher in the surface water sampled in July (39.55 ± 4.78 particles L^-1) than in March (22.00 ± 4.87 particles L^-1) (p < 0.05). The average microplastic abundance of snails across all sites was 28.13 ± 4.18 particles, among which the Q2 site has significantly higher microplastic abundance than station Q3-Q5 (p < 0.05). Microplastic particles 10-100 μm in size predominated in both the surface water and the snails. By contrast, the proportions of microplastic particles 200-500 μm in size were substantially smaller. The measured microplastic pollution load and microplastic pollution risk indices in the surface water indicated that the current microplastic pollution level in the Qing River was moderate from upstream to downstream. Moreover, the potential adverse effects of microplastic particles on snails remain unclear. Further research is required to elucidate small-size microplastics' environmental fate and potential ecological risks in urban rivers.

Biomonitoring of heavy metals accumulation in molluscs and echinoderms collected from southern coastal India

Distribution of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in molluscan and echinoderm species collected from Kerala and Gulf of Mannar in Southern India is presented. Atomic absorption spectrometry was used to determine metal concentrations. Concentrations of metals showed a descending order of Zn > Cu > Pb > Cd > Cr. Zn and Cu might have originated from both natural and man-made sources. However, Cd, Cr, and Pb could have strong anthropogenic influences such as harbour activities and untreated industrial and agricultural runoff. Bioaccumulation factor (BAF) value of Cd in two edible bivalves from Munambam is slightly greater than one. Regular consumption of Cd-loaded shellfish can cause serious health hazards and concerns to humans. BAF results showed that Zn, Cu, Pb, and Cd were more bioaccumulated and beyond the threshold limits in certain species. It is evident that consumption of shellfish from the Kerala coastal waters may have adverse health impacts to the consumers.

The paralytic shellfish toxin effect on bioenergetic constituents of the fishery resource Chorus giganteus (Gastropoda: Muricidae)

Alexandrium catenella, one of the most common harmful microalgae observed in southern Chile, produces paralytic shellfish toxins, which can affect many organisms throughout the trophic chain. This research evaluated how paralytic shellfish toxins affected the principal bioenergetic constituents and fatty acids composition of the carnivorous snail Chorus giganteus. Snails were separated into a "toxic" group that was fed the toxic clam Mulinia edulis (which was previously fed A. catenella), and a "non-toxic" group, fed non-toxic clams. Both groups were kept under these conditions for 63 days. Our results indicated no difference in the ingestion rate of toxic versus non-toxic snails; however, a higher protein level was identified in toxic snails. The total lipid content proved to be no different in toxic versus non-toxic snails; although, an effect of the toxic diet on the fatty acid profile of C. giganteus was observed. High levels of essential polyunsaturated fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in toxic snails, were identified. Our results suggest that exposure to paralytic shellfish toxins, through diet, may cause changes in the biochemical composition of C. giganteus, which may have a subsequent impact on its energetic physiology.

Endemicity and radiation in waterfalls of the Western Ghats: The genus Cremnoconchus (Gastropoda: Littorinidae)

Snails of the genus Cremnoconchus - the only freshwater members of the gastropod family Littorinidae - are endemic to the spray zones of numerous waterfalls in the Western Ghats of India. Cremnoconchus consists of nine described and possibly numerous undescribed species as many of these appear to be restricted to specific waterfalls. This is the first attempt at resolving the relationships between the various species in this genus and establishing its monophyly in the family. Further, we also undertake species delimitation analysis to characterize cryptic diversity in this group. Phylogenetic analyses based on nuclear and mitochondrial genes support the monophyly of Cremnoconchus within the family. A fossil-calibrated Bayesian time tree suggests that this freshwater lineage diverged from its marine counterparts around 90.40 million years ago. The separation of Cremnoconchus from its marine ancestors might have been facilitated by the break-up of Gondwana or fluctuating sea levels during this period. Species delimitation analysis retrieved 12 potentially undescribed species in this group. These species formed two distinct clades in the phylogeny, one largely confined to the northern Western Ghats and the other to the central Western Ghats. Species belonging to the northern and central Western Ghats seem to have separated around 56.11 mya, i.e. after the northern Western Ghats were formed. Additionally, spatial isolation due to the patchiness of suitable habitats (waterfalls) and low mobility might have facilitated their diversification.

Gut microbiome of century-old snail specimens stable across time in preservation

BACKGROUND

Museum biological specimens provide a unique means of gathering ecological information that spans wide temporal ranges. Museum specimens can also provide information on the microbial communities that persist within the host specimen. Together, these provide researchers valuable opportunities to study long-term trends and mechanisms of microbial community change. The effects of decades-long museum preservation on host-microbial communities have not been systematically assessed. The University of Colorado's Museum of Natural History has densely sampled Oreohelix strigosa (Rocky Mountainsnail) for the past century; many are preserved in ethanol, which provides an excellent opportunity to explore how the microbiome changes across time in preservation.

RESULTS

We used 16S rRNA (ribosomal ribonucleic acid) gene amplicon sequencing to examine Oreohelix strigosa gut microbiomes from museum specimens across a 98-year range, as well as within short-term preservation treatments collected in 2018. Treatment groups included samples extracted fresh, without preservation; samples starved prior to extraction; and samples preserved for 1 month, 6 months, and 9 months. General microbiome composition was similar across all years. Sample groups belonging to specific years, or specific short-term treatments, showed unique associations with select bacterial taxa. Collection year was not a significant predictor of microbial richness, though unpreserved short-term treatments showed significantly higher richness than preserved treatments. While the year was a significant factor in microbiome composition, it did not explain much of the variation across samples. The location was a significant driver of community composition and explained more of the variability.

CONCLUSIONS

This study is the first to examine animal host-associated microbiome change across a period of nearly one century. Generally, geographic location was a greater factor in shaping gut microbiome composition, rather than a year collected. Consistent patterns across this temporal range indicate that historic specimens can answer many ecological questions surrounding the host-associated microbiome. Video Abstract.

Environmental conditions affect the food quality of plastic associated biofilms for the benthic grazer Physa fontinalis

With an ever-increasing amount of plastic pollution in the various aquatic ecosystems around the world, the effects on organisms are still not fully understood. Most studies focus on direct effects posed by plastic intake or entanglement, but plastic debris can also affect primary production of biofilms and have an indirect impact on its consumers. This study investigates the primary production on three common plastic types in freshwater and its food quality for a benthic grazer. We hypothesized that different polymer types affect biofilm composition as well as the life parameters of its consumers. We incubated polyethylene (PE), polyethylene terephthalate (PET) and polystyrene (PS) as well as glass (control) in a productive freshwater creek for natural biofilm establishment. To account for changes in the environmental conditions, the experiment was conducted twice during winter and late spring, respectively. These biofilms were offered to the freshwater gastropod Physa fontinalis as sole food source. Growth and reproduction of the snails were measured to monitor sublethal effects. Additionally, biofilm composition was observed using confocal laser scanning microscopy (CLSM). In winter, snails feeding off PET and PE showed a significantly lower egg production and lower growth rates were observed on PET. No such effects occurred in spring. CLSM data revealed, that algal growth was significantly lower on PE and PET during the winter treatment compared to PS and glass. Since we could only find these effects during the colder and darker months (January-March), the microbial colonization on PE and PET was inhibited by the substrate under less favorable conditions of temperature and light. Hence, benign conditions may mask the adverse effects of microplastic on food webs. Our findings show that future studies on the plastisphere will need to consider such variations to further understand the influence of plastic pollution on primary production and higher trophic levels.

Metal loadings in estuarine bivalve and gastropod shellfish in response to socioeconomic development in watershed

Metal contamination in estuary was monitored globally using shellfish while estuarine metal loadings were influenced by socioeconomic development in watershed, i.e., a watershed-estuary chain effect. Socioeconomic pattern of metal loadings in estuarine shellfish has scarcely been studied. Eight metals and metalloids (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) highly associated with anthropogenic activities were quantified in tissue and shell of bivalves and gastropods (two feeding-habits) among 7 estuaries along the Southeastern China coast in the period 2016-2019. Results indicated that Cu and Zn in shellfish had the greatest loadings at 1,663 and 6,828 mg kg^-1 dry mass in tissue and 387 and 151 mg kg^-1 dry mass in shell, respectively, in the most developed Estuary Yong. Metal loadings in tissue and shell of bivalves (6 common species) and gastropods (3 common species) in the estuaries were highly associated with urbanization and socioeconomic indicators in their watersheds. The socioeconomic patterns had evident shellfish class-specification and metal-dependency due to the feeding-habit. The class-specification was confirmed by the fractionation of stable isotope compositions for the socioeconomic pattern of Pb loadings in both tissue and shell. In short, both shellfish class-specification and metal-dependency hinted that multi-bioindicators might be required for a comprehensive understanding of the estuarine environment quality, in particular at two dimensions of water and sediment.

Long-term exposure to environmental diclofenac concentrations impairs growth and induces molecular changes in Lymnaea stagnalis freshwater snails

As pharmaceutical substances are highly used in human and veterinary medicine and subsequently released in the environment, they represent emerging contaminants in the aquatic compartment. Diclofenac (DCF) is one of the most commonly detected pharmaceuticals in water and little research has been focused on its long-term effects on freshwater invertebrates. In this study, we assessed the chronic impacts of DCF on the freshwater gastropod Lymnaea stagnalis using life history, behavioral and molecular approaches. These organisms were exposed from the embryo to the adult stage to three environmentally relevant DCF concentrations (0.1, 2 and 10 μg/L). The results indicated that DCF impaired shell growth and feeding behavior at the juvenile stage, yet no impacts on hatching, locomotion and response to light stress were noted. The molecular findings (metabolomics and transcriptomic) suggested that DCF may disturb the immune system, energy metabolism, osmoregulation and redox balance. In addition, prostaglandin synthesis could potentially be inhibited by DCF exposure. The molecular findings revealed signs of reproduction impairment but this trend was not confirmed by the physiological tests. Combined omics tools provided complementary information and enabled us to gain further insight into DCF effects in freshwater organisms.

Withering syndrome induced gene expression changes and a de-novo transcriptome for the Pinto abalone, Haliotis kamtschatkana

In the abalone and Candidatus Xenohaliotis californiensis (Ca. Xc) system, the Ca. Xc bacterium infects abalone digestive tissues and leads to extreme starvation and a characteristic "withering" of the gastropod foot. First identified in black abalone in California after an El Niño event, withering syndrome (WS) has caused large declines in wild black and captive white abalone on the northeastern Pacific coast, but disease resistance levels are species-, and possibly population-specific. This study compared gene expression patterns in the digestive gland of Ca. Xc-exposed and unexposed (control) Pinto abalone (Haliotis kamtschatkana), a particularly susceptible species. Lab-induced Ca. Xc infections were followed over 7 months and RNAseq was used to identify differential gene expression. Exposed Pinto abalone showed distinct changes in expression of 68 genes at 3 and 7 months post-infection relative to those in control animals. Upregulation of an orexin-like receptor (which is involved in feeding signaling) and a zinc peptidase-like region (many amino peptidases are zinc peptidases) in animals infected for 7 months indicates that animals with Ca. Xc infection may be starving and upregulating processes associated with feeding and digestion. Other groups of differentially expressed genes (DEGs) were upregulated or downregulated across control and exposed individuals over the 7-month experiment, including DEG groups that likely correspond to early disease state and to general stress response of being held in captivity. No patterns emerged in genes known to be involved in molluscan immune response, despite this being an expectation during a 7-month infection; digestion-related genes and unannotated DEGs were identified as targets for future research on potential immune response to WS in abalone.

Toll like receptors and their evolution in the lymnaeid freshwater snail species Radix auricularia and Lymnaea stagnalis, key intermediate hosts for zoonotic trematodes

One of the major evolutionarily conserved pathways in innate immunity of invertebrates is the toll-like receptor (TLR) pathway. However, little is known of the TLR protein family in gastropod molluscs despite their role in the transmission of human diseases, especially the common lymnaeid freshwater snail species Radix auricularia and Lymnaea stagnalis, key intermediate hosts of zoonotic trematodes. Using comparative genomics and gene prediction approaches utilising the freshwater snail Biomphalaria glabrata genome as a reference ten putative TLR proteins were identified in both R. auricularia and L. stagnalis. Phylogenetic analyses revealed that unlike other molluscs the lymnaeid species also possessed class 1 TLRs, previously thought to be unique to B. glabrata. Gene duplication events were also seen across the TLR classes in the lymnaeids with several of the genes appearing to exist as potential tandem elements in R. auricularia. Each predicted TLR was shown to possess the typical the leucine-rich repeat extracellular and TIR intracellular domains and both single cysteine clusters and multiple cysteine clusters TLRs were identified in both lymnaeid species. Principle component analyses of 3D models of the predicted TLRs showed that class 1 and 5 proteins did not cluster based on similarity of structure, suggested to be potential adaptation to a range of pathogens. This study provides the first detailed account of TLRs in lymnaeids and affords a platform for further research into the role of these proteins into susceptibility and compatibility of these snails with trematodes and their role in transmission.

Nivar cyclonic impacts on mollusk habitat destruction in Parangipettai, southeast coast of Tamil Nadu, India: A case study

Tropical storms form in the Bay of Bengal every year during the pre-monsoon season, affecting the coastal communities and the marine ecosystem. On November 25, 2020, severe cyclone Nivar impacted the southeast coast of Tamil Nadu, causing massive damage to marine benthic species. The study found that the Nivar cyclone's high velocity wind impacted tidal currents and damaged sediment compartments. This phenomenonhas immensely affected the benthic communities of Mudasalodai, Parangipettai, Puthupettai, Samiyarpettai, and Kumarapettai. Post-Nivar cyclone observations revealed massive bivalve and gastropod mortality. The two molluscan species lost their habitats due to the tremendous cyclone effect. More than 1 lakh Mactra violacea were emigrated from Parangipettai and 5 lakh Turritella acutangula and T. attenuata were emigrated from Samiyarpettai. Thus, the Nivar cyclone severely damaged mollusk habitats along India's southeast coast. The severe cyclonic storm Nivar disrupted the southeast coast of India, with losses amounting to over $600 million.

Temporal dynamic of biofilms enhances the settlement of the central-Mediterranean reef-builder Dendropoma cristatum (Biondi, 1859)

Research on marine invertebrate settlement provides baseline knowledge for restoration technique implementation, especially for biogenic engineers with limited dispersion ability. Previously, we determined that the maturity of a biofilm strongly enhances the settlement of the vermetid reef-builder Dendropoma cristatum. To elucidate settlement-related biofilm features, here we analyse the structure and composition of marine biofilms over time, through microscopic observations, eukaryotic and prokaryotic fingerprinting analyses and 16S rDNA Illumina sequencing. The vermetid settlement temporal increase matched with the higher biofilm coverage on the substratum and the reduction of the eukaryotic abundance and diversity. The prokaryotic assemblage become, over time, more similar to that found on the reef-associated biofilm. Vermetids may detect these differences and selectively settle on those biofilms which show an advantageous structure and composition. These outcomes may support the production of ideal substrates for vermetid colonization and their further translocation to repopulate degraded reefs.

Microplastics pollution in the intertidal limpet, Nacella magellanica, from Beagle Channel (Argentina)

Microplastics (MPs) have been identified in diverse marine invertebrates; however, there are few studies on limpets. This study aimed to evaluate and compare the presence of MPs in Nacella magellanica among sites of the Beagle Channel with different degree of anthropogenic influence. Intertidal limpets were sampled in three sites: Ushuaia Bay (UB) (inside Ushuaia city), a site with high anthropogenic influence owing to population growth, and fisheries, industrial and port activities; Ensenada Zaratiegui (EZ) and Playa Larga (PL) (west and east of Ushuaia city, respectively), both sites with a certain degree of environmental protection and low anthropogenic influence. MPs were isolated from the whole soft tissue of individuals by oxidative digestions with H₂O₂ (30%; 1:10 w/v). MPs occurrence was 100% in organisms from UB and EZ, whereas 90% in PL. Limpets from UB showed 10 ± 6.69 MPs/ind and 2.22 ± 0.78 MPs/g ww, while in PL and EZ there were 2.90 ± 2.02 MPs/ind and 0.96 ± 0.94 MPs/g ww; and 5.60 ± 2.59 MPs/ind and 2.41 ± 1.47 MPs/g ww, respectively. Fibres were the most abundant MPs type, followed by fragments and films. Fibres and films were identified as semi-synthetic cellulose and, although the polymer matrix of fragments was masked by copper phthalocyanine, one of them could be identified as polystyrene. As expected, the highest abundance of MPs was found in UB. However, a lower abundance of particles was detected in PL (downstream of UB) than in EZ (upstream of UB). This could be due to the influence of both the main current of the Beagle Channel and fluvial discharges, reducing the buoyancy of MPs. More studies are needed to understand the contribution of regional and local features to the accumulation of MPs in these environments and their interaction with the biota.

Aerobic and anaerobic movement energetics of hybrid and pure parental abalone

The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly understood. We used pure blacklip (Haliotis rubra) and greenlip (Haliotis laevigata) abalone, as well as their hybrid, to test whether differences in movement and/or aerobic versus anaerobic energy use are linked to a purported increased growth rate in hybrids. Abalone were acclimated to control (16 °C) and typical summer temperatures (23 °C), each with oxygen treatments of 100% air saturation (O₂sat) or 70% O₂sat. The experiment then consisted of two phases. During the first phase (chronic exposure), movement and oxygen consumption rates (ṀO₂) of abalone were measured during a 2 day observation period at stable acclimation conditions. Additionaly, lactate dehydrogenase (LDH) and tauropine dehydrogenase (TDH) activities were measured. During phase two (acute exposure), O₂sat was raised to 100% for abalone acclimated to 70% O₂sat followed by an acute decrease in oxygen to anoxia for all acclimation groups during which movement and ṀO₂ were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting ṀO₂, LDH and TDH activities, however, were similar between abalone types but were increased at 23 °C compared to 16 °C. During the acute exposure, the initial increase to 100% O₂sat for individuals acclimated to 70% O₂sat resulted in increased movement compared to individuals acclimated to 100% O₂sat for hybrids and H. rubra when compared within type of abalone. Similarly, ṀO₂ during spontaneous activity of all three types of abalone previously subjected to 70% O₂sat increased above those at 100% O₂sat. When oxygen levels had dropped below the critical oxygen level (P_crit), movement in hybrids and H. laevigata increased up to 6.5-fold compared to movement above P_crit. Differences in movement and energy use between hybrids and pure species were not marked enough to support the hypothesis that the purportedly higher growth in hybrids is due to an energetic advantage over pure species.

Caution ahead: reassessing the functional morphology of the respiratory organs in amphibious snails

After a long hiatus, interest in the morphology of the respiratory organs in apple snails (Ampullariidae, Caenogastropoda) and its functional and evolutionary bearings is making a comeback. The variability in the morphology of the gill and lung and its link to different lifestyles and patterns of air dependency within the Ampullariidae make research on the morphology of the respiratory organs particularly suitable for approaching the evolution of terrestriality in animals. Additionally, morphology is a valuable source of hypotheses regarding the several functions the ampullariid respiratory organs have besides respiration. However, this is an underexplored field that only recently has incorporated ultrastructural and three-dimension visualization tools and in which more research is much needed, particularly, comparisons between species representing the diversity within the Ampullariidae. In this paper, I examine Mueck, Deaton & Lee’s (2020a) assessment of the morphology of the gill and lung of Pomacea maculata and compare it with earlier and contemporary studies on other ampullariid species. I show that Mueck, Deaton & Lee’s paper combines significant morphological misinterpretations, conceptual and terminological mistakes, and crucial literature omissions. I also reinterpret their results and point to the similarities and differences between them and available data on other ampullariids.

Characterization of the gut microbiome in wild rocky mountainsnails (Oreohelix strigosa)

Background

The Rocky Mountainsnail (Oreohelix strigosa) is a terrestrial gastropod of ecological importance in the Rocky Mountains of western United States and Canada. Across the animal kingdom, including in gastropods, gut microbiomes have profound effects on the health of the host. Current knowledge regarding snail gut microbiomes, particularly throughout various life history stages, is limited. Understanding snail gut microbiome composition and dynamics can provide an initial step toward better conservation and management of this species.

Results

In this study, we employed 16S rRNA gene amplicon sequencing to examine gut bacteria communities in wild-caught O. strigosa populations from the Front Range of Colorado. These included three treatment groups: (1) adult and (2) fetal snails, as well as (3) sub-populations of adult snails that were starved prior to ethanol fixation. Overall, O. strigosa harbors a high diversity of bacteria. We sequenced the V4 region of the 16S rRNA gene on an Illumina MiSeq and obtained 2,714,330 total reads. We identified a total of 7056 unique operational taxonomic units (OTUs) belonging to 36 phyla. The core gut microbiome of four unique OTUs accounts for roughly half of all sequencing reads returned and may aid the snails’ digestive processes. Significant differences in microbial composition, as well as richness, evenness, and Shannon Indices were found across the three treatment groups.

Conclusions

Comparisons of gut microbiomes in O. strigosa adult, fetal, and starved samples provide evidence that the host internal environments influence bacterial community compositions, and that bacteria may be transmitted vertically from parent to offspring. This work provides the first comprehensive report on the structure and membership of bacterial populations in the gastropod family Oreohelicidae and reveals similarities and differences across varying life history metrics. Strong differentiation between these life history metrics demonstrates the need for wider sampling for studies of dynamics of the snail gut microbiome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00111-6.

Where three snail species attach while emersed in relation to heterogenous substrate temperatures underneath intertidal boulders

Mobile intertidal gastropods can employ behavioural thermoregulation to mitigate thermal stress, which may include retreating under boulders when emersed. However, little is known about how gastropod occupancy of under-boulder habitats is associated with any variations in substrate temperature that exist under boulders. Thermal imagery was used to measure the temperature of boulder lower surfaces and investigate how three snail species were associated at low tide with the maximum and average temperatures underneath grey siltstone and quartzite. Lower boulder surfaces had heterogeneous temperatures, with grey siltstone having temperature gradients and quartzite temperature showing mosaics. Temperature differences between the hottest and coolest gradient or mosaic locations were >5 °C; thus there was a range of temperatures that snails could interact with. All three snail species occupied cooler parts of temperature mosaics or gradients, avoiding the hottest areas. Stronger associations were detected on the hotter grey siltstone and for the more-thermally sensitive Nerita atramentosa and Diloma concameratum. Even though snails were associated with cooler areas, some individuals were still exposed to extreme substratum heat (>50 °C). These results suggest that gastropod thermoregulatory behaviour is far more complex than simply retreating underneath boulders at low tide, as there is also a range of under-boulder temperatures that they interact with. Untangling interactions between intertidal gastropods and heterogenous substrate temperatures is important given rocky seashores already represent a thermally-variable and potentially-stressful habitat, which may be exacerbated further given predictions of warming temperatures associated with climate change.

Sea snail (Hexaplex trunculus) and sea cucumber (Holothuria polii) as potential sentinel species for organic pollutants and trace metals in coastal ecosystems

The seasonal bioaccumulation of trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorinated pesticides (OCPs) in sea snail (Hexaplex trunculus) and sea cucumber (Holothuria polii) from Mar Menor lagoon were characterised. The highest concentrations of p,p'-DDE were detected in the central and south part of Mar Menor lagoon. However, the highest concentrations of metals in sea snail and holothurians were detected in the influence area of El Beal wadi. Biomagnification factors (BMF) in sea snail from cockle (sea snail-cockle concentration ratio) were higher than 5 for metal and organochlorinated compounds. However, similar concentrations were observed in both species for PAHs due to gastropods capability of metabolising these pollutants. Consequently, sea snail is proposed as a sentinel for trace metals, PCBs and OCPs in the coastal lagoons, not only due to its bioaccumulation and biomagnification capacity but also the easy sampling and amply distribution in many coastal areas.

Entomopathogenic nematode-gastropod interactions

Entomopathogenic nematodes (EPNs) infect and kill insects and have been successfully used in the biological control of some insect pests. Slugs and snails are known to be significant pests of agriculture and serve as vectors for disease-causing microbes that can affect crops and humans. The potential of EPNs to be used in the biological control of gastropods has not been well-studied. The few studies that have been performed on the efficacy of EPNs in controlling gastropod pests and vectors were reviewed. Suggested criteria for further assessments of EPN-gastropod interactions are: Dose of EPNs used, length of infection assays, host biology, nematode biology and development, and Koch's postulates. There are provocative data suggesting that EPNs may be useful biological control agents against gastropod pests of agriculture and vectors of disease, though additional studies using the suggested criteria are needed, including the publication of negative data or studies where EPNs were not efficacious or successful in controlling gastropods.

Long-term thermal acclimation drives adaptive physiological adjustments of a marine gastropod to reduce sensitivity to climate change

Ocean warming is predicted to challenge the persistence of a variety of marine organisms, especially when combined with ocean acidification. While temperature affects virtually all physiological processes, the extent to which thermal history mediates the adaptive capacity of marine organisms to climate change has been largely overlooked. Using populations of a marine gastropod (Turbo undulatus) with different thermal histories (cool vs. warm), we compared their physiological adjustments following exposure (8-week) to ocean acidification and warming. Compared to cool-acclimated counterparts, we found that warm-acclimated individuals had a higher thermal threshold (i.e. increased CT_max by 2 °C), which was unaffected by the exposure to ocean acidification and warming. Thermal history also strongly mediated physiological effects, where warm-acclimated individuals adjusted to warming by conserving energy, suggested by lower respiration and ingestion rates, energy budget (i.e. scope for growth) and O:N ratio. After exposure to warming, warm-acclimated individuals had higher metabolic rates and greater energy budget due to boosted ingestion rates, but such compensatory feeding disappeared when combined with ocean acidification. Overall, we suggest that thermal history can be a critical mediator of physiological performance under future climatic conditions. Given the relatively gradual rate of global warming, marine organisms may be better able to adaptively adjust their physiology to future climate than what short-term experiments currently convey.

Metal accumulation and biomineralisation of coastal and mangrove-associated molluscs of Palk Bay, Southeastern India

The present study aimed to determine metal accumulation levels in tissue and biomineralisation in shells of 20 species of molluscs (13 gastropods and 7 bivalves) from Palk Bay, India. In most cases, metal concentrations in the tissues were higher than in the shells of the same species collected from same location, meaning that in many cases biomineralisation factors of metal ratios were <1. The highest biomineralisation factor for Cd was detected in Melampus sincaporensis (3.72 ± 0.1) from the Thondi mangrove, for Pb in Cerithidea cingulata (2.51 ± 0.17) from the Vattanam mangrove, for Cu in Melampus sincaporensis (0.88 ± 0.2) from the Thondi mangrove, and for Zn in Cerithidea cingulata (0.93 ± 0.3) from the Devipattinam mangrove. In most cases, metal concentrations were higher than reported in previous studies but were within the maximum limits stated by national and international regulatory agencies. Variations in the biomineralisation factor of metal ratios among the molluscan species likely stems from variations in bioaccumulation efficiency, selectivity of individual organisms, and availability of metals in the mangrove and coastal environments.

Evaluation of single and combined effects of two pharmaceuticals on the marine gastropod Phorcus lineatus enzymatic activity under two different exposure periods

Pharmaceutical drugs are among the most used chemicals for human and veterinary medicines, aquaculture and agriculture. Pharmaceuticals are environmentally persistent, biologically active molecules, thereby having the potential to exert biological effects on non-target species. Among the most used pharmaceuticals, one may find salicylic acid (SA), a non-steroid anti-inflammatory drug (NSAID) that acts by inhibiting the enzymes cyclooxigenases; it is also possible to identify acetazolamide (ACZ), a diuretic that acts by inhibiting the activity of carbonic anhydrase (CA). In this work, the effects of both single and combined effects of these drugs were assessed on the marine gastropod Phorcus lineatus, by measuring key enzymatic activities, namely carbonic anhydrase (CA) and cyclooxygenase (COX), under two different exposure periods (14 and 28 days). We observed no straightforward pattern of enzymatic response in all treatments of both pharmaceuticals, on both analyzed tissues (gut and gills), and for both exposure regimes. We assume that this species is not responsive to the hereby tested pharmaceuticals, a finding that may be due to general mechanisms of response to adverse conditions, such as reduction of metabolism, of heart rate, of filtration rates, and to the increase production of mucus. All these functional adaptations can mitigate the deleterious effects caused by adverse conditions, without triggering biochemical responses. In conclusion, the species P. lineatus seems not to be sensitive in terms of these specific enzymatic pathways to these contaminants, under the adopted conditions.

Morphological grounds for the obligate aerial respiration of an aquatic snail: functional and evolutionary perspectives

The freshwater caenogastropod family Ampullariidae is emerging as a model for a variety of studies, among them, the evolution of terrestriality. A common character of the family is that all its members bear a lung while retaining the ancestral gill. This ensures that many ampullariids are able to inhabit poorly oxygenated waters, to bury in the mud during estivation, and to temporarily leave the water, in some species for oviposition. To these characters Pomacea canaliculata (Caenogastropoda, Ampullariidae) adds that is an obligate air-breather. In a recent paper, we showed the gill epithelium of P. canaliculata has a set of characteristics that suggest its role for oxygen uptake may be less significant than its role in ionic/osmotic regulation and immunity. We complement here our morphological investigation on the respiratory organs of P. canaliculata by studying the lung of this species at the anatomical (3D reconstructions of the blood system and nerve supply), histological and ultrastructural levels. The circulation of the gill and the lung are interconnected so that the effluence of blood from the gill goes to the lung where it completes oxygenation. Besides that, we found the lung cavity is lined by a pavement epithelium that encloses an anastomosing network of small blood spaces resting over a fibromuscular layer, which altogether form the respiratory lamina. The pavement cells form a blood-gas barrier that is 80–150 nm thick and thus fulfils the requirements for an efficient gas exchanger. Tufts of ciliary cells, together with some microvillar and secretory cells, are interspersed in the respiratory lamina. Rhogocytes, which have been proposed to partake in metal depuration and in the synthesis of hemocyanin in other gastropods, were found below the respiratory lamina, in close association with the storage cell tissue. In light of these findings, we discuss the functional role of the lung in P. canaliculata and compare it with that of other gastropods. Finally, we point to some similarities in the pattern of the evolution of air dependence in this family.

Reassignment of crispatene, isolation and chemical characterization of stachydrine, isolated from the marine mollusk Elysia crispata

The molluscan genus Elysia Risso, 1818 (Sacoglossa) is composed of shell-less herbivore sea slugs. From these marine organisms, polyketides such as polypropynates have been isolated and showed cytotoxic, antibiotic, and antifungal, and antiviral properties. In this work, we reported the isolation, and structure elucidation of two compounds isolated from marine mollusk E. crispata. Both compounds isolated, crispatene (1) and stachydrine (2), were purified by HPLC. The chemical structure of compound (1) was reassigned through 1D and 2D NMR experiments and high-resolution electrospray ionization mass spectrometry (HRESIMS). On the other hand, this is the first time that compound (2) has been found in this species of mollusk or the marine environment, previously, (2) has only been found in terrestrial plants or bacteria in symbiosis with plants.

An Integrated and Multibiomarker approach to delineate oxidative stress status of Bellamya bengalensis under the interactions of elevated temperature and chlorpyrifos contamination

Synergistic effects of warming on bioconcentration and receptiveness of pollutants are still poorly unravelled in conjunction with cellular and molecular responses. The present study addressed the impact of an environmental relevant dose of chlorpyrifos (organophosphate pesticide), under control (25 °C) and elevated levels of temperature (30 °C, 35 °C) in Bellamya bengalensis, a freshwater gastropod for 60 days across various endpoints. Multiple levels of biomarkers were measured: growth conditions (organ to flesh weight ratio, condition index), oxidative stress status (SOD, CAT, GST, LPO) and DNA damage (Comet assay-3^rd, 30^th and 60^th days only) after acute (24, 48 and 72 h) and long-term exposures (10^th, 20^th, 30^th, 40^th, 50^th and 60^th days). An integrated biomarker response (IBR) strategy was adapted to amalgamate results generated from various biomarkers to assess organism's vulnerability to pesticide pollution and how it may shift with warming climate. Significant changes were observed in growth conditions under longer exposure periods. Acute as well as long-term exposures enhanced the antioxidant and detoxification enzyme activity. DNA damage was extensive under longer exposure to stress howbeit was also significantly escalated under acute severe warming. Antioxidant and detoxification mechanisms fell short in counteracting cellular level damage. The IBR results indicated long-term acclimation of B. bengalensis to elevated temperatures and pesticide contamination lead to an improved tolerance level howbeit, acute stress was more detrimental. This study provided evidence for the efficiency of employing an integrated biomarker approach for B. bengalensis in future bio-monitoring studies.

Intraspecific genetic variation for anesthesia success in a New Zealand freshwater snail

Intraspecific genetic variation can drive phenotypic variation even across very closely related individuals. Here, we demonstrate that genetic differences between snails are a major contributor to wide variation in menthol anesthesia success in an important freshwater snail model system, Potamopyrgus antipodarum. Anesthesia is used to immobilize organisms for experiments and surgical procedures and to humanely mitigate pain. This is the first example of which we are aware of a role for genetic variation in anesthesia success in a mollusk. These findings highlight the fact that using only one strain or lineage for many experiments will not provide a full picture of phenotypic variation, demonstrate the importance of optimizing biomedically relevant techniques and protocols across a variety of genetic backgrounds, illuminate a potential mechanism underlying previously documented challenges in molluscan anesthesia, and set the stage for powerful and humane manipulative experiments in P. antipodarum.

Microplastic pollution in tropical estuary gastropods: Abundance, distribution and potential sources of Klang River estuary, Malaysia

Microplastics receive global attention due to its strong presence in marine and freshwater organisms. Yet, there are few studies on estuarine organisms. This baseline study evaluates the abundance and distribution of microplastics in the gastropods of a tropical estuary in Selangor, Malaysia. The abundance of microplastics ranged from 0.50 to 1.75 particles/g or from 0.25 to 0.88 particles/individual. The variation in microplastic distribution between the upper and lower estuary indicates that the microplastics originated from the urbanised area of the Klang River estuary. Microplastic sizes varied from 30 to 1850 μm, with the majority being between 300 and 1000 μm (57%). Characteristics of microplastics were dominant for fibres (91%) with black colour (50%). Polyethylene-propylene-diene (PE-PDM) and polyester were the main polymer materials. Assessing the contamination of gastropods by microplastics provides insight into the possibility of utilising gastropods as bioindicators that could be used for monitoring and baseline studies.

Parasite-host ecology: the limited impacts of an intimate enemy on host microbiomes

BACKGROUND

Impacts of biotic stressors, such as consumers, on coral microbiomes have gained attention as corals decline worldwide. Corallivore feeding can alter coral microbiomes in ways that contribute to dysbiosis, but feeding strategies are diverse - complicating generalizations about the nature of consumer impacts on coral microbiomes.

RESULTS

In field experiments, feeding by Coralliophila violacea, a parasitic snail that suppresses coral growth, altered the microbiome of its host, Porites cylindrica, but these impacts were spatially constrained. Alterations in microbial community composition and variability were largely restricted to snail feeding scars; basal or distal areas ~ 1.5 cm or 6-8 cm away, respectively, were largely unaltered. Feeding scars were enriched in taxa common to stressed corals (e.g. Flavobacteriaceae, Rhodobacteraceae) and depauperate in putative beneficial symbionts (e.g. Endozoicomonadaceae) compared to locations that lacked feeding.

CONCLUSIONS

Previous studies that assessed consumer impacts on coral microbiomes suggested that feeding disrupts microbial communities, potentially leading to dysbiosis, but those studies involved mobile corallivores that move across and among numerous individual hosts. Sedentary parasites like C. violacea that spend long intervals with individual hosts and are dependent on hosts for food and shelter may minimize damage to host microbiomes to assure continued host health and thus exploitation. More mobile consumers that forage across numerous hosts should not experience these constraints. Thus, stability or disruption of microbiomes on attacked corals may vary based on the foraging strategy of coral consumers.

Toxicity of dinonylnaphthalene sulfonates to Pimephales promelas and epibenthic invertebrates

Dinonylnaphthalene sulfonic acids (NSAs) are high production volume chemicals that are used primarily as additives in a wide range of industrial products (i.e., coatings, sealants, fuels, metal-extractants, paints, rubber materials). This study examined the effect of three NSA congeners on freshwater organisms: barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS). Chronic effects were characterized by exposing fertilized fathead minnow eggs to sediment-associated NSAs and measuring various developmental and growth endpoints for 21 d. No effects in hatch success and larval growth were observed when fathead minnow eggs were exposed to CaDNS and DNDS concentrations up to 246 and 798 μg/g dry weight, respectively, in spiked sediment (~2% organic carbon). However, when NSAs were associated with substrate containing no organic carbon (sand), EC50s for fathead minnow hatch success, larval growth, biomass production, and overall survival were 58.3, 18.8, 15.5, and 13.8 μg/L, respectively, for CaDNS. Acute effect characterization was also conducted in water-only exposures for the three NSA congeners using the freshwater amphipod Hyalella azteca, the pulmonate snail Planorbella pilsbryi, and larval freshwater mussels Lampsilis cardium and Lampsilis siliquoidea. The sulfonate salts (BaDNS and CaDNS) were significantly more acutely toxic to all tested invertebrates in the water-only exposures, with LC50s ranging from 0.47 to 12.1 μg/L, compared to DNDS (LC50s ≥ 98.2 μg/L). This is the first study to provide empirical data on the aquatic toxicity of three NSA congeners.

Uptake of Paralytic Shellfish Toxins by Blacklip Abalone (Haliotis rubra rubra Leach) from direct exposure to Alexandrium catenella microalgal cells and toxic aquaculture feed

The Tasmanian abalone fishery represents the largest wild abalone resource in the world, supplying close to 25% of the annual wild-caught global harvest. Prompted by the need to manage Paralytic Shellfish Toxin (PST) contamination of Blacklip Abalone (Haliotis rubra rubra) from east coast Tasmania, the uptake of toxins by this species is investigated in a land-based, controlled aquaculture setting. Abalone were exposed to either live Alexandrium catenella microalgal cultures or PST contaminated feed pellets during a 28 day exposure period and toxins quantified in viscera, foot muscle and epipodium tissues. PST profiles of abalone foot tissues were dominated by saxitoxin and neosaxitoxin, whilst viscera more closely resembled those of the toxin source (A. catenella cells rich in gonyautoxin 1&4 and 2&3 or feed pellets containing A. catenella extracts rich in these analogues). This indicates direct uptake of PST in the viscera via browsing/grazing on the pellet and /or sedimented microalgal cells. After exposure to A. catenella cell culture, PST concentrations in the foot (muscle + epipodium) were on average 8 times higher than in the viscera. Higher toxicity of foot tissue was caused by higher PST content of the epipodium (up to 1,085 µg STX.2HCl equiv. kg^-1), which despite its small contribution to total animal weight significantly added to the overall toxin burden. Higher PST levels in the abalone foot suggest that toxin monitoring programmes may not need to routinely analyse both foot and viscera, potentially allowing for a 50% reduction of analytical costs. This option is being further investigated with continuing field studies.

Both maternal and embryonic exposure to mild hypoxia influence embryonic development of the intertidal gastropod Littorina littorea

There is growing evidence that maternal exposure to environmental stressors can alter offspring phenotype and increase fitness. Here, we investigate the relative and combined effects of maternal and developmental exposure to mild hypoxia (65 and 74% air saturation, respectively) on the growth and development of embryos of the marine gastropod Littorina littorea Differences in embryo morphological traits were driven by the developmental environment, whereas the maternal environment and interactive effects of maternal and developmental environment were the main driver of differences in the timing of developmental events. While developmental exposure to mild hypoxia significantly increased the area of an important respiratory organ, the velum, it significantly delayed hatching of veliger larvae and reduced their size at hatching and overall survival. Maternal exposure had a significant effect on these traits, and interacted with developmental exposure to influence the time of appearance of morphological characters, suggesting that both are important in affecting developmental trajectories. A comparison between embryos that successfully hatched and those that died in mild hypoxia revealed that survivors exhibited hypertrophy in the velum and associated pre-oral cilia, suggesting that these traits are linked with survival in low-oxygen environments. We conclude that both maternal and developmental environments shape offspring phenotype in a species with a complex developmental life history, and that plasticity in embryo morphology arising from exposure to even small reductions in oxygen tensions affects the hatching success of these embryos.

Effect of photoperiod and light intensity on learning ability and memory formation of the pond snail Lymnaea stagnalis

Natural light is regarded as a key regulator of biological systems and typically serves as a Zeitgeber for biological rhythms. As a natural abiotic factor, it is recognized to regulate multiple behavioral and physiological processes in animals. Disruption of the natural light regime due to light pollution may result in significant effects on animal learning and memory development. Here, we investigated whether sensitivity to various photoperiods or light intensities had an impact on intermediate-term memory (ITM) and long-term memory (LTM) formation in the pond snail Lymnaea stagnalis. We also investigated the change in the gene expression level of molluscan insulin-related peptide II (MIP II) is response to the given light treatments. The results show that the best light condition for proper LTM formation is exposure to a short day (8 h light) and low light intensity (1 and 10 lx). Moreover, the more extreme light conditions (16 h and 24 h light) prevent the formation of both ITM and LTM. We found no change in MIP II expression in any of the light treatments, which may indicate that MIP II is not directly involved in the operant conditioning used here, even though it is known to be involved in learning. The finding that snails did not learn in complete darkness indicates that light is a necessary factor for proper learning and memory formation. Furthermore, dim light enhances both ITM and LTM formation, which suggests that there is an optimum since both no light and too bright light prevented learning and memory. Our findings suggest that the upsurge of artificial day length and/or night light intensity may also negatively impact memory consolidation in the wild.

Conchology Variations in Species Identification of Pachychilidae (Mollusca, Gastropoda, Cerithiodea) through Multivariate Analysis

Pachychilidae is one of the freshwater gastropod family which was previously known under the Potamididae and Thiaridae families. Studies on freshwater gastropods especially on conchcology examinantions are still inadequate compared to marine gastropods. Morphological and morphometric studies of gastropods are practically used to identify and differentiate between species and necessary to complement molecular studies due to its low cost and tolerable resolving power of discrimination. The aim of the current study is to provide information on morphological and morphometric characteristics of Pachychilidae in Bintulu, Sarawak stream. A total of 20 individuals from each species of Sulcospira testudinaria, Sulcospira schmidti, Brotia siamensis, and Tylomelania sp. from Pachychilidae familiy were collected at three different sites from a small stream within the Bintulu area. Fourteen measurement of shell morphometrics were converted into proportioned ratios and analysed for univariate and multivariate analysis. Three shell morphometric (Aperture width, AW; Whorl width, WW2; and, Interior anterior length, AINL) of Pachychilidae indicated significant differences (P < 0.05) between species. However, multivariate analysis revealed that these shell morphometrics are pre-eminent factors to discriminate genus Sulcospira, Brotia and Tylomelania, as well as between Sulcospira species. This current study also suggests that these three characteristics are unique to Sulcospira species due to strong distinction among species. Findings on these three characteristics are significant for Sulcospira spp. as this study is the first shell morphometric report on the Pachychilidae species in Sarawak.

Laccase and catecholoxidase activities contribute to innate immunity in slipper limpets, Crepidula fornicata

The slipper limpet Crepidula fornicata is an invasive, non-native, marine species found throughout the coastal waters of southern England and Wales, UK. These limpets are considered to blight commercial shellfish banks, notably oysters, yet little is known about their disease-carrying capacity or their immunobiology. To address the latter, we isolated haemolymph (blood) from limpets and tested for the presence of the immune-enzyme phenoloxidase. Invertebrate phenoloxidases produce melanic polymers from simple phenolic substrates, which are deployed in the presence of pathogens because of their potent microbicidal and microbiostatic properties. We used a series of established substrates (e.g., tyrosine, hydroquinone) and inhibitors (e.g., 4-hexylresorcinol, benzoic acid) to target three distinct enzymes: laccase (para-diphenoloxidase), catecholoxidase (ortho-diphenoloxidase) and tyrosinase (monophenoloxidase). We confirmed laccase and catecholoxidase activities and characterised their kinetic properties across temperature and pH gradients (5-70 °C and 5-10, respectively). Crucially, we demonstrated that products derived from such laccase and catecholoxidase activities reduced significantly the numbers of colony-forming units of both Gram-positive and Gram-negative bacteria in vitro. We further screened limpet tissues for signs of melanin using wax histology, and found cells replete with eumelanin-like pigments and lipofuscin in the digestive gland, connective tissues, barrier epithelia and gills. Our data represent the first account of enzyme-based antibacterial defences, notably laccase, in C. fornicata.

A quarter century of recovery of the whelk Thais orbita from tributyltin pollution off Perth, Western Australia

Imposex is a condition in which females of dioecious marine snails develop rudimentary male characteristics. It is caused by tributyltin (TBT) used as an antifoulant in vessel paints since the late 1960s. Following the 2008 international ban on TBT, a decreasing rate of imposex has been observed worldwide. In Western Australia, imposex surveys of the whelk Thais orbita up to 2011 in the Perth metropolitan area suggested a decreasing trend but a significant recovery has not been confirmed. Collection of T. orbita from 11 sites in 2019 demonstrated a virtually complete recovery from imposex. Although it is generally accepted that male snails are not affected by TBT, the historical data set allowed confirmation that the male penis is of similar size in T. orbita collected at heavily affected sites and at relatively unaffected sites. Similarly, imposexed female snails had similar shell lengths to female snails at non-impacted sites.

DNA Footprints: Using Parasites to Detect Elusive Animals, Proof of Principle in Hedgehogs

Simple Summary

Nocturnal and elusive animals are notoriously difficult to count—hedgehogs being a prime example. Therefore, any reliable way to demonstrate the presence of a particular animal, within a given area, would be a valuable addition to many ecologists’ tool kits. The proposed method is based upon the idea that you can find a parasite, specific to a vertebrate animal of interest that has a life stage within an invertebrate host. Molecular detection of these parasites is then carried out in the more abundant and easily collected invertebrate intermediate host. The key to this proposed method is the specificity of the parasite to the vertebrate animal and its detection in the invertebrate intermediate hosts. Crenosoma striatum is specific to hedgehogs and was chosen as the parasite to develop the molecular survey tool for hedgehogs, an elusive nocturnal species of considerable interest at present. Results revealed the presence of the nematode only at a site known to be inhabited by hedgehogs confirming the potential of this method to improve the accuracy of recording hedgehog populations.

Abstract

The Western European Hedgehog (Erinaceous europaeus) is a nocturnal animal that is in decline in much of Europe, but the monitoring of this species is subjective, prone to error, and an inadequate basis for estimating population trends. Here, we report the use of Crenosoma striatum, a parasitic nematode specific to hedgehogs as definitive hosts, to detect hedgehog presence in the natural environment. This is achieved through collecting and sampling the parasites within their intermediate hosts, gastropoda, a group much simpler to locate and sample in both urban and rural habitats. C. striatum and Crenosoma vulpis were collected post-mortem from the lungs of hedgehogs and foxes, respectively. Slugs were collected in two sessions, during spring and autumn, from Skomer Island (n = 21), which is known to be free of hedgehogs (and foxes); and Pennard, Swansea (n = 42), known to have a healthy hedgehog population. The second internal transcribed spacer of parasite ribosomal DNA was used to develop a highly specific, novel, PCR based multiplex assay. Crenosoma striatum was found only at the site known to be inhabited by hedgehogs, at an average prevalence in gastropods of 10% in spring and autumn. The molecular test was highly specific: One mollusc was positive for both C. striatum and C. vulpis, and differentiation between the two nematode species was clear. This study demonstrates proof of principle for using detection of specific parasite DNA in easily sampled intermediate hosts to confirm the presence of an elusive nocturnal definitive host species. The approach has great potential as an adaptable, objective tool to supplement and support existing ecological survey methods.

Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado

A survey of 2,368 vertebrate fossils from the Upper Jurassic Mygatt-Moore Quarry (MMQ) (Morrison Formation, Brushy Basin Member) in western Colorado revealed 2,161 bone surface modifications on 884 specimens. This is the largest, site-wide bone surface modification survey of any Jurassic locality. Traces made by invertebrate actors were common in the assemblage, second in observed frequency after vertebrate bite marks. Invertebrate traces are found on 16.174% of the total surveyed material and comprise 20.148% of all identified traces. Six distinct invertebrate trace types were identified, including pits and furrows, rosettes, two types of bioglyph scrapes, bore holes and chambers. A minimum of four trace makers are indicated by the types, sizes and morphologies of the traces. Potential trace makers are inferred to be dermestid or clerid beetles, gastropods, an unknown necrophagous insect, and an unknown osteophagus insect. Of these, only gastropods are preserved at the site as body fossils. The remaining potential trace makers are part of the hidden paleodiversity from the North American Late Jurassic Period, revealed only through this ichnologic and taphonomic analysis. Site taphonomy suggests variable, but generally slow burial rates that range from months up to 6 years, while invertebrate traces on exposed elements indicate a minimum residence time of five months for carcasses with even few preserved invertebrate traces. These traces provide insight into the paleoecology, paleoclimate, and site formation of the MMQ, especially with regards to residence times of the skeletal remains on the paleolandscape. Comprehensive taphonomic studies, like this survey, are useful in exploring patterns of paleoecology and site formation, but they are also rare in Mesozoic assemblages. Additional work is required to determine if 16.174% is typical of bulk-collected fossils from Jurassic ecosystems in North America, or if the MMQ represents an unusual locality.

An effective method for evaluation of microplastic contaminant in gastropod from Taihu Lake, China

Microplastics are ubiquitous in the environment. The isolation and characterization of microplastics can change, enabling science to elucidate the fate of microplastics in organisms. The main objective of the present study was to develop a rapid and effective method for the isolation, characterization, and quantification of microplastics from gastropod, and then evaluate the microplastic pollution in wild freshwater snails using the developed method. The whole tissue of gastropod Bellamya aeruginosa was spiked with microplastics derived from cosmetic products to optimize the tissue digestion and microplastic identification process. Optimum digestion of soft tissue was performed using a mixture of Tris-HCl, proteinase K, and KOH. Recovery of microplastics from the tissue digests, as determined by microscopy and infrared spectroscopy, was 89 ± 5%. The entire procedure could be completed within 30 h. Application of the procedure to wild freshwater snail B. aeruginosa collected from Taihu Lake revealed that 90~100% of the sampled snails accumulated 1 to 4 types of microplastics including poly(vinyl acetate), polyethylene terephthalate, polystyrene, and polyamides. In summary, a quick method was developed for the isolation and identification of microplastics from gastropod tissues, and the application of the method revealed the presence of microplastics in snails inhabiting Taihu Lake, China.

Classical and computed tomographic anatomical analyses in a not-so-cryptic Alviniconcha species complex from hydrothermal vents in the SW Pacific

The chemosymbiotic gastropod Alviniconcha (Provannidae), first described in 1988, is one of the most emblematic hydrothermal-vent taxa described from the Central Indian Ridge and the Southwest (SW) Pacific. Symbiotic bacteria found in the gill of Alviniconcha are thought to be their principal source of nutrition. In the SW Pacific, species distributions for A. kojimai, A. boucheti - and to a lesser extent A. strummeri - overlap. While Alviniconcha species do not appear to truly co-exist in these highly energetic but spatially limited habitats, certain species regularly co-occur within a single vent field and in rare instances, the same edifice. Past research suggests that SW-Pacific Alviniconcha species might aggregate around fluids with distinct geothermal profiles. These small-scale distribution patterns have been attributed to differences in their symbiont assemblages or host physiologies. However, little is known about the anatomy of most Alviniconcha species, beyond that detailed for the type species Alviniconcha hessleri, whose geographic range does not overlap with other congeners. In fact, species within this genus are currently described as cryptic, despite the absence of any comparative morphological studies to assess this. To test whether the genus is genuinely cryptic and identify any functional differences in host anatomy that might also mediate habitat partitioning in SW Pacific species, the current study examined the morphoanatomy of A. kojimai, A. boucheti and A. strummeri from the Fatu Kapa vent field, an area of hydrothermal activity recently discovered north of the Lau Basin near the Wallis and Futuna Islands and the only known example where all three species occur within adjacent vent fields. A combination of detailed dissections, histology and X-ray computed tomography demonstrate that A. kojimai, A. strummeri and A. boucheti are readily identifiable based on shell morphology and ornamentation alone, and therefore not truly cryptic. These traits provide a rapid and reliable means for species identification. However, aside from some subtle differences in radular morphology, these species of Alviniconcha exhibit conserved anatomical features, providing no evidence that functional host anatomy is implicated in habitat partitioning. This provides support for the current belief that host-species distributions are probably governed by symbiont-mediated physiological factors.

Linking energy budget to physiological adaptation: How a calcifying gastropod adjusts or succumbs to ocean acidification and warming

Accelerating CO₂ emissions have driven physico-chemical changes in the world's oceans, such as ocean acidification and warming. How marine organisms adjust or succumb to such environmental changes may be determined by their ability to balance energy intake against expenditure (i.e. energy budget) as energy supports physiological functions, including those with adaptive value. Here, we examined whether energy budget is a driver of physiological adaptability of marine calcifiers to the near-future ocean acidification and warming; i.e. how physiological energetics (respiration rate, feeding rate, energy assimilation and energy budget) relates to adjustments in shell growth and shell properties of a calcifying gastropod (Austrocochlea concamerata). We found that ocean warming boosted the energy budget of gastropods due to increased feeding rate, resulting in faster shell growth and greater shell strength (i.e. more mechanically resilient). When combined with ocean acidification, however, the gastropods had a substantial decrease in energy budget due to reduced feeding rate and energy assimilation, leading to the reduction in shell growth and shell strength. By linking energy budget to the adjustability of shell building, we revealed that energy availability can be critical to determine the physiological adaptability of marine calcifiers to the changing oceanic climate.