Scallop Argopecten Purpuratus Research Articles

Impacts of climate-driven upwelling intensification on the microbiota and health of cultivated scallops

The scallop Argopecten purpuratus plays a pivotal role as an economic resource cultivated in regions where climate change may intensify the coastal upwelling. This process has the potential to impact host-microbiota interactions. Hence, we conducted a field study to investigate the effects of varying upwelling intensities on hemolymph and gill microbiota dynamics (utilizing 16S rRNA gene sequencing), as well as the pathological state of A. purpuratus maintained in culture systems. Helicobactereaceae and Arcobactereaceae emerged as the prevailing families within both the hemolymph and gills. In contrast to the period of weak upwelling, the phase characterized by intensified upwelling revealed notable shifts in the abundance of bacterial community members, thereby leading to implications for the functional potential of the hemolymph microbiota. Notably, environmental factors played a substantial role in shaping the microbial community, accounting for 82–96% of the observed variation. Among these factors, wind, oxygen, and temperature exerted the most influence. During intensified upwelling, the abundance of Arcobactereaceae increased from 27% to 36% within gills and from 43% to 55% within hemolymph. Conversely, Helicobactereaceae decreased, particularly within gills, from 15% to 8% during the same period. Significantly, bacteria with fermentation capabilities, such as Colwellia, along with those involved in sulfur cycle processes, such as Arcobactereaceae, Desulfobulbaceae, and Desulfobacteraceae, exhibited an elevated representation during the period of intensified upwelling. This suggests potential nutritional advantages for A. purpuratus. However, the intense upwelling phase also saw an overrepresentation of potentially pathogenic bacteria for mollusks, including Francisella halioticida, Vibrio, and Photobacterium. Moreover, histopathological examination revealed heightened hemocytic infiltration, the presence of granulomatous “swirl” lesions, and a potential Apicomplexan parasite during this intensified upwelling period. These findings underscore the importance of the adaptability of host-microbiota interactions and the potential risks of pathogenicity for cultivated A. purpuratus within the context of ongoing and future environmental changes. Therefore, continuous monitoring of pathogen emergence and immune status evaluation during intensified upwelling periods are crucial for successful A. purpuratus aquaculture.

Trade-off between growth and reproduction in Argopecten purpuratus (L.) scallops exposed to medium-term hypoxia and acidification

Peruvian bays that are home to aquatic organisms of commercial interest are increasingly affected by hypoxia and low pH events. These stressors produce unfavorable conditions for the aquatic fauna, leading to mass mortality events. In this study, we evaluated the ecophysiological responses of the scallop Argopecten purpuratus exposed to moderate hypoxia (20% DO saturation) and low pH (OA, pH 7.4) using a 2 × 2 factorial design. We found that a 51-day exposure to low pH (OA treatment) had greater negative effects on A. purpuratus performances than hypoxia (lower survival and decreased clearance and calcification rates), but stimulated early gonad maturation. The survival rate was 1.3-fold higher under hypoxia than under acidic treatment. The interaction between hypoxia and low pH had an antagonistic effect on survival, since the combined treatment (HOA) resulted in lower scallop mortality than the single stress treatments. Calcification was negatively affected by all stress treatments, whereas hypoxia and OA both stimulated gametogenesis. OA treatment resulted in higher frequencies of previtellogenic and vitellogenic oocytes, greater gonad coverage area, and lower frequency of atretic oocytes, suggesting higher reproductive potential. HOA was positively related to oocyte development and high frequency of post-vitellogenic and atretic oocytes. These results suggest that, due to hypoxia and low pH, feeding is reduced and energy allocation prioritizes scallop gonad maturation. This trend would have negative effects on scallop growth and calcification, while increased reproduction under environmental stress could mitigate the effect on recruitment.

Treatment of wastewater coming from culture of scallop Argopecten purpuratus using O3/photo-Fenton and membrane distillation processes

The treatment and recovery of industrial wastewater is a necessary contribution to solve the water scarcity problems that affect an increasing part of the world's population. One of the industries that produces a larger amount of polluted wastewater is aquaculture. The aim of this research is the evaluation of the use of a novel treatment line consisting of coagulation/flocculation, filtration, advanced oxidation by ozone/solar photo-Fenton, and membrane distillation (MD) arranged in series to treat wastewater coming from the wash of a Chilean aquaculture facility of the scallop Argopecten purpuratus. In the pretreatment section, the use of a flocculant based on polyacrylamide improved the removal of suspended solids up to 86 %, higher than that achieved with FeCl3. Combining the effects of the oxidation and separation stages, the chemical oxygen demand (COD) was reduced up to 97 % in a single pass. Moreover, salt rejection in MD was higher than 99.8 %, which allowed to obtain freshwater with acceptable quality. Permeate flux was almost constant around 18 L/h/m2, suggesting that no permanent fouling was formed onto the membrane surface.The treatment line presented in this work allows therefore to deal with highly contaminated wastewaters, contributing thus to an appropriate waste management and avoiding severe environmental damages.

Reproductive Conditioning of the Peruvian Scallop Argopecten purpuratus in Different Environments

Obtaining viable Argopecten purpuratus seeds faces challenges, especiallyci the unpredictability of the marine environment and high production costs in hatcheries. However, improving the method of "Broodstock Conditioning In Hatcheries" is key to ensure permanent seed supplies by minimizing the dependence on marine conditions and by maximizing economic viability in hatcheries. In an effort to overcome these barriers, broodstock were conditioned into two different environments: (a) Natural Environment: Natural marine conditions located in Bahía Inglesa, Atacama Region, Chile. (b) Hatchery: Laboratory conditions to achieve gonadal maturation, spawning induction, fertilization and larval development. The purpose of this research was to evaluate how the type of reproductive conditioning affects the reproductive potential and nutritional quality of the progeny. Both methods were successful at inducing the necessary maturity for reproduction, obtaining viable gametes and larvae. On the other hand, it was observed that in the natural environment, the oocytes and D larvae reached a greater size and nutritional value, being the most significant differences with (p < 0.05): the size of the D larvae reached figures of 95.8 ± 3.1 μm and 91.2 ± 2.7 μm in the environment and hatchery, respectively; the lipid content in dry mass was 25.2 ± 3.1 mg g−1 and 13.5 ± 1.9 mg g−1 for the natural environment and hatchery, respectively. Although quality indicators in hatcheries were slightly lower compared to the natural environment, the possibility of conditioning A. purpuratus broodstock independently of environmental variability highlights the importance of further optimizing broodstock conditioning aspects in hatcheries that would allow more predictable and sustainable production.

Scallop larvae resistant to a pathogenic Vibrio harbor host-associated bacteria with probiotic potential

The breeding of the scallop Argopecten purpuratus is threatened by mass mortality events mostly caused by bacterial pathogens of the genus Vibrio affecting larvae and spat cultivated in hatcheries. A strong genetic basis for the resistance of A. purpuratus larvae to vibriosis has been demonstrated, which is associated with an efficient energy metabolism and immunocompetence. However, various factors, including the microbiota composition, have a notable impact on the outcome of an infection in numerous animal models, affecting their resistance. In this context, we aimed to explore the possible contribution of host-associated bacteria to the resistance of scallop larvae to Vibrio bivalvicida VPAP30. To achieve this, we isolated culturable bacteria from four scallop families displaying contrasted resistance to VPAP30 infection. We taxonomically assigned 75 bacterial isolates by 16S rDNA sequencing, and we found that 34 isolates were exclusively associated with resistant larvae. Then, 8 isolates were pre-selected as potential probiotics based on their exclusivity to the resistant families and bibliographic records of their use. Results highlighted three isolates displaying potential, belonging to the genera Psychrobacter, Hydrogenophaga, and Shewanella. The three isolates displayed in vitro antagonistic activity against VPAP30 and a protective effect on scallop veliger larvae against infection. We observed three main aspects of this protective effect: scallop larvae pretreated with each of the three probiotic candidates showed (i) no mortality after 24 h infection, (ii) an earlier induction of immune pattern recognition receptors, and (iii) no increase in total Vibrio spp. counts after infection with VPAP30. The findings demonstrated that scallop larvae resistant to vibriosis carry distinct bacteria possessing probiotic properties suitable for the rearing of scallop larvae. This study reinforces the significance of host resistance-related microorganisms as a potential source for discovering novel endogenous probiotics with biotechnological applications.

A Diet Rich in HUFAs Enhances the Energetic and Immune Response Capacities of Larvae of the Scallop Argopecten purpuratus.

Massive mortalities in farmed larvae of the scallop Argopecten purpuratus have been associated with pathogenic Vibrio outbreaks. An energetic trade-off between development-associated demands and immune capacity has been observed. Given that highly unsaturated fatty acids (HUFAs) are essential nutrients for larval development, we evaluated the effect of diets based on microalgae low and high in HUFAs (LH and HH, respectively) on the energetic condition and the immune response of scallop larvae. The results showed that the HH diet increased cellular membrane fluidity in veliger larvae. The routine respiration rate was 64% higher in the HH-fed veligers than in the LH-fed veligers. Additionally, the metabolic capacity tended to be higher in the HH-fed veligers than in the LH-fed veligers after the Vibrio challenge. After the challenge, the HH-fed veligers presented higher transcript induction of ApTLR (immune receptor) and ApGlys (immune effector) genes, and the HH-fed pediveligers presented higher induction of ApLBP/BPI1 (antimicrobial immune effector) gene, than the LH-fed larvae. Furthermore, the HH-fed veligers controlled total Vibrio proliferation (maintaining near basal levels) after the bacterial challenge, while the LH-fed veligers were not able to control this proliferation, which increased three-fold. Finally, the HH-fed larvae showed 20-25% higher growth and survival rates than the LH-fed veligers. Overall, the results indicated that the administration of a HH diet increases cell membrane fluidity and energy metabolic capacity, which in turn enhances immunity and the ability to control Vibrio proliferation. The administration of microalgae high in HUFAs would be a promising strategy for improving scallop larval production efficiency.

First Report, Characterization and Pathogenicity of Vibrio chagasii Isolated from Diseased Reared Larvae of Chilean Scallop, Argopecten purpuratus (Lamarck, 1819).

Two Vibrio strains (VPAP36 and VPAP40) were isolated from moribund-settled larvae of the Chilean scallop Argopecten purpuratus during vibriosis outbreaks that occurred in two commercial scallop larvae hatcheries located in the Inglesa and Tongoy bays in Northern Chile. The strains were identified as Vibrio chagasii using phenotypic characterization and whole genome sequence analysis. Both strains exhibited the phenotypic properties associated with virulence, gelatin hydrolysis and β-hemolysis, whereas only VPAP36 produced phospholipase and only VPAP40 produced caseinase. The whole genome analysis showed that the strains harbored genes encoding for the virulence factors, the EPS type II secretion system, and Quorum Sensing (auto-inductor 1 and auto-inductor 2), whereas genes encoding a metalloproteinase and a capsular polysaccharide were detected only in the VPAP40 genome. When challenge bioassays using healthy 11-day-old scallop larvae were performed, the V. chagasii VPAP36 and VPAP40 strains exhibited significant (p < 0.05) differences in their larval lethal activity, producing, after 48 h, larval mortalities of 65.51 ± 4.40% and 28.56 ± 5.35%, respectively. Otherwise, the cell-free extracellular products of the VPAP36 and VPAP40 strains produced larval mortalities of 20.86 ± 2.40% and 18.37 ± 2.40%, respectively, after 48 h of exposure. This study reports for the first time the isolation of V. chagasii from the massive larval mortalities of the farmed scallop (Argopecten purpuratus) in Chile, and demonstrates the pathogenic activity of V. chagasii towards the Chilean scallop, the second most important species for Chilean mariculture.

Implementation of seed collection programs for the recovery of Argopecten purpuratus populations in the La Rinconada marine reserve (Antofagasta, Chile)

Abstract ‘La Rinconada Marine’ Reserve (MR), Chile was created in 1997 to preserve the genetic stock of the scallop Argopecten purpuratus and eventually to supply seed to areas outside of the reserve and support aquaculture activities. Data from biological and fisheries monitoring of A. purpuratus as well as environmental conditions in the MR are available for the period from 1993 to 2009. The continuous extraction of A. purpuratus from La Rinconada MR in Chile, without a science‐based exploitation plan, has not only decreased the abundance and population structure of the species but has also significantly affected seed settlement in artificial collectors and population recruitment. Therefore, the goals of the MR have not been achieved. This review of biological and fishing studies of A. purpuratus in La Rinconada MR provides a basis for the implementation of a sustainable programme for the natural collection of A. purpuratus seed for population recovery. A. purpuratus recruitment varies substantially between years and is not strongly related to the size of the parental population. Larval collection and recruitment depend on environmental events (El Niño‐Southern Oscillation) and biological substrate availability (Rhodymenia red algae). These factors produce a bentho‐pelagic decoupling between parental abundance, larval production and subsequent recruitment of A. purpuratus that limits stock recovery in the MR. To address the poor population status of A. purpuratus in the MR, recovery of the adult population is needed. Therefore, an assisted collection and recruitment strategy is proposed to increase the population and enable the generation of surplus seed, fulfilling the initial aims of La Rinconada MR.

Size matters: Physiological sensitivity of the scallop Argopecten purpuratus to seasonal cooling and deoxygenation upwelling-driven events

Environment imposes physiological constraints which are life-stage specific as growth-maintenance and/or growth-reproduction energetic requirements are size and volume-dependent. The scallop Argopecten purpuratus, one of the most important bivalve species subjected to fishery and aquaculture along the Humboldt Current System, inhabits spaces affected by continuous changes in temperature, pH, oxygen, and food availability driven by remote and local oceanographic processes. Specifically, in Chile, this species is mainly cultured in central-north Chile where is permanently affected by upwelling events of dissimilar intensity and duration which generate local conditions of acidification, deoxygenation, and cooling with different magnitudes. However, to date, it remains unknown how this economic valuable resource is physiologically affected throughout its life cycle by the continuous environmental changes driven by upwelling events of different intensities and duration along the year. Here, for the first time, A. purpuratus life-stage physiological sensitivity was assessed at a seasonal scale through a year-field experiment where growth, calcification, and survivorship were evaluated. Our study shows how seasonal differences in the upwelling phenology (here measured as changes in temperature, dissolved oxygen, pH, and primary productivity, but also as the number, duration, and intensity of cooling and de-oxygenation events) notably impacted the A. purpuratus physiological performance from juvenile to adult life-stages. This was especially noticeable during the spring season which showed the most intense cooling and deoxygenation events driven by stronger favorable-upwelling winds and the lowest growth and gross calcification rates (the highest decalcification rates) where adult stages showed the lowest performance. On the other hand, A. purpuratus survivorship was not significantly affected by upwelling intensity which would be providing evidence of the high physiological flexibility and well-locally adapted is this species to fluctuating and occasional stressful environmental conditions. Our results are significantly relevant in the climate change context as some upwelling systems are at risk to change shortly (i.e., an upwelling intensification in frequency and intensity) as a consequence of changes in the atmospheric pressures that modulate favourable-upwelling winds. These changes may certainly increase the climate related-risks of the entire socio-ecological systems related to the fishery and aquaculture of A. purpuratus along the Humboldt Current System.

Differential gene expression analysis in the scallop Argopecten purpuratus exposed to altered pH and temperature conditions in an upwelling-influenced farming area

Increased carbon dioxide in the atmosphere and its absorption across the ocean surface will alter natural variations in pH and temperature levels, occurring in coastal upwelling ecosystems. The scallop Argopecten purpuratus, one of the most economically important species farmed in northern Chile, has been shown to be vulnerable to these environmental drivers. However, the regulatory responses at the gene-level of scallops to these climate stressors remain almost unknown. Consequently, we used an orthogonal experimental design and RNAseq approach to analyze the acute effects of variability in pH and temperature on gene expression in the muscle tissue of A. purpuratus. In respect to control conditions (pH ~ 8.0/ 14 °C), the influence of low pH (~ 7.7) and temperature (14 °C) induced the activation of several genes associated with apoptotic signaling pathways and protein localization to plasma membrane. Elevated temperature (18 °C) and pH (~8.0) conditions increased the expression of transcripts associated with the activation of muscle contraction, regulation, and sarcomere organization effects on muscle tissue. In scallops exposed to low pH and elevated temperature, the genes expressed were differentially associated with the oxidation-reduction process, signal translation, and positive regulation of GTPase activity. These results indicated that the differentially expressed genes under the experimental conditions tested are mainly related to the mitigation of cellular damage and homeostasis control. Our results add knowledge about the function of the adductor muscle in response to stressors in scallops. Furthermore, these results could help in the identification of molecular biomarkers of stress necessary to be integrated into the aquaculture programs for the mitigation of climate change.

The Gill Microbiota of Argopecten purpuratus Scallop Is Dominated by Symbiotic Campylobacterota and Upwelling Intensification Differentially Affects Their Abundance.

Despite the great importance of gills for bivalve mollusks (respiration, feeding, immunity), the microbiota associated with this tissue has barely been characterized in scallops. The scallop Argopecten purpuratus is an important economic resource that is cultivated in areas where coastal upwelling is intensifying by climate change, potentially affecting host-microbiota interactions. Thus, we first characterized the bacterial community present in gills from cultivated scallops (by 16S rRNA gene amplicon sequencing) and assessed their stability and functional potential in animals under farm and laboratory conditions. Results showed that under both conditions the gill bacterial community is dominated by the phylum Campylobacterota (57%), which displays a chemoautotrophic potential that could contribute to scallop nutrition. Within this phylum, two phylotypes, namely symbionts A and B, were the most abundant; being, respectively, taxonomically affiliated to symbionts with nutritional functions in mussel gills, and to uncultured bacteria present in coral mucus. Additionally, in situ hybridization and scanning electron microscopy analyses allowed us to detect these symbionts in the gills of A. purpuratus. Given that shifts in upwelling phenology can cause disturbances to ecosystems, affecting bacteria that provide beneficial functions to the host, we further assessed the changes in the abundance of the two symbionts (via qPCR) in response to a simulated upwelling intensification. The exposure to combined decreasing values in the temperature, pH, and oxygen levels (upwelling conditions) favored the dominance of symbiont B over symbiont A; suggesting that symbiont abundances are modulated by these environmental changes. Overall, results showed that changes in the main Campylobacterota phylotypes in response to upwelling intensification could affect its symbiotic function in A. purpuratus under future climate change scenarios. These results provide the first insight into understanding how scallop gill-microbial systems adapt and respond to climate change stressors, which could be critical for managing health, nutrition, and scallop aquaculture productivity.

Coastal livelihood resilience to abrupt environmental change: the role of social capital in a Peruvian bay

Abrupt environmental change, such as sudden shifts in temperature or salinity, can severely alter the functioning of marine ecosystems and cause dramatic impacts on the associated social systems. Resource users, who rely on ecosystem services provided by the ocean, are particularly vulnerable to such drastic events. Functioning social relationships (social capital) have recently been suggested as a key driver for recovery after disaster. Here, we study how small-scale fishers who conduct sea-ranching of the Peruvian bay scallop Argopecten purpuratus in Northern Peru dealt with the literal wipe-out of their target resources caused by the Coastal El Niño (CEN) of 2017 that heavily impacted the entire region. Adopting an ego-network approach complemented by qualitative information from expert interviews, we investigated how resource users drew on their social networks to cope with the disaster. Results suggested a significant positive correlation between more desirable post-disaster trajectories and the number of helpful social links of scallop farmer associations. Disentangling the temporal aspect of this pattern, we found that social capital established before the disaster was driving this correlation. Importantly, both economic and non-economic links were contributing to the observed patterns. This study emphasizes the importance of social capital for dealing with the effects of disasters following natural events. Having extensive social networks increases the capacity to mobilize resources and information when needed and is associated with more efficient recovery after abrupt environmental change. Mechanisms to foster and enhance social capital are key for preventive management actions aiming to build resilience within vulnerable communities facing accelerating global change.

Effect of low pH on growth and shell mechanical properties of the Peruvian scallop Argopecten purpuratus (Lamarck, 1819)

Dissolution of anthropogenic CO2 modifies seawater pH, leading to ocean acidification, which might affect calcifying organisms such as bivalve mollusks. Along the Peruvian coast, however, natural conditions of low pH (7.6–8.0) are encountered in the habitat of the Peruvian scallop (Argopecten purpuratus), as a consequence of the nearby coastal upwelling influence. To understand the effects of low pH in a species adapted to these environmental conditions, an experiment was performed to test its consequences on growth, calcification, dissolution, and shell mechanical properties in juvenile Peruvian scallops. During 28 days, scallops (initial mean height = 14 mm) were exposed to two contrasted pH conditions: a control with unmanipulated seawater presenting pH conditions similar to those found in situ (pHT = 7.8) and a treatment, in which CO2 was injected to reduce pH to 7.4. At the end of the experiment, shell height and weight, and growth and calcification rates were reduced about 6%, 20%, 9%, and 10% respectively in the low pH treatment. Mechanical properties, such as microhardness were positively affected in the low pH condition and crushing force did not show differences between pH treatments. Final soft tissue weights were not significantly affected by low pH. This study provides evidence of low pH change shell properties increasing the shell microhardness in Peruvian scallops, which implies protective functions. However, the mechanisms behind this response need to be studied in a global change context.

Materialities, discourses and governance: scallop culture in Sechura, Peru

ABSTRACT This paper looks at the institutional emergence, particularly space rights, within the culture of the Peruvian bay scallop (Argopecten purpuratus) in Sechura Bay. The institutional system developed within a period of 20 years from an open-access, gold rush scenario to a rather structured, formal activity – however, still relies on a lot of informality. This work uses the matrix provided by the material dependency framework presented in this special issue distinguishing between nature, human and hybrid-made materialities that influence the emergence of institutional structures, on the one axis and path-, inter- and goal dependencies on the other axis. In this work, we argue that existing natural (high environmental risks associated with scallop culture in this setting), hybrid (need to process quickly) and human-made (export-oriented production) materialities have shaped different path dependencies in institutional development in favour of larger firms who gradually took over the control of scallop production from small-scale producers, who in turn became piece wage labourers. Yet, the realities of both actors are necessarily intertwined, with informal loop holes being intentionally left open, shaping different institutional solutions over time. Applying the material dependency framework shows how materialities and goal dependencies are intertwined in this particular case of scallop bottom aquaculture.

A g-type lysozyme from the scallop Argopecten purpuratus participates in the immune response and in the stability of the hemolymph microbiota

Lysozymes are antimicrobial acid hydrolases widely distributed in nature. They are located inside the cells in lysosomes, or they are secreted to the extracellular space, where they can lyse the cell wall of certain species of bacteria via hydrolysis of the peptidoglycan. Thus, lysozymes are bacteriolytic enzymes and play a major biological role in biodefense, as these enzymes can act as antibacterial and immune-modulating agents. In this study, we characterized a g-type lysozyme from the scallop Argopecten purpuratus named ApGlys. The cDNA sequence comprises an open reading frame (ORF) of 600 nucleotides, codifying for a putative protein of 200 amino acids with a signal peptide of 18 amino acids. The deduced mature protein sequence displays a molecular weight of 20.07 kDa and an isoelectric point (pI) of 6.49. ApGlys deduced protein sequence exhibits conserved residues associated with catalytic activity and substrate fixation in other g-type lysozymes. The phylogenetic analysis revealed a high degree of identity of ApGlys with other mollusk g-type lysozymes, which form a restricted and separated clade from the vertebrate lysozymes. ApGlys transcripts were constitutively and highly expressed in the digestive gland, and it was induced in hemocytes and gills of scallops after an immune challenge. Furthermore, the ApGlys protein was located inside hemocytes of immunostimulated scallops, determined by immunofluorescence analysis. Finally, the transcript silencing of ApGlys by RNA interference led to an increase of total culturable bacteria from the scallop hemolymph. Furthermore, we detected a higher diversity of the bacterial community in ApGlys-silenced scallops and an imbalance of certain bacterial groups present in the hemolymph by 16S rDNA deep amplicon sequencing. Overall, our results showed that ApGlys is a new member of scallop lysozymes that is implicated in the immune response and in the microbial homeostasis of A. purpuratus hemolymph.

Biomechanical Characterization of Scallop Shells Exposed to Ocean Acidification and Warming.

Increased carbon dioxide levels (CO2) in the atmosphere triggered a cascade of physical and chemical changes in the ocean surface. Marine organisms producing carbonate shells are regarded as vulnerable to these physical (warming), and chemical (acidification) changes occurring in the oceans. In the last decade, the aquaculture production of the bivalve scallop Argopecten purpuratus (AP) showed declined trends along the Chilean coast. These negative trends have been ascribed to ecophysiological and biomineralization constraints in shell carbonate production. This work experimentally characterizes the biomechanical response of AP scallop shells subjected to climate change scenarios (acidification and warming) via quasi-static tensile and bending tests. The experimental results indicate the adaptation of mechanical properties to hostile growth scenarios in terms of temperature and water acidification. In addition, the mechanical response of the AP subjected to control climate conditions was analyzed with finite element simulations including an anisotropic elastic constitutive model for a two-fold purpose: Firstly, to calibrate the material model parameters using the tensile test curves in two mutually perpendicular directions (representative of the mechanical behavior of the material). Secondly, to validate this characterization procedure in predicting the material’s behavior in two mechanical tests.

Analysis and gonadal localization of Speedy A mRNA transcript, a novel gene associated with early germline cells in the scallop, Argopecten purpuratus

The Speedy A (spdya) gene is a member of the Speedy/RINGO family, encoding a spdya protein associated with cellular cycle and meiosis in vertebrates. Results from genetic analyses indicated spdya conditional knockout mice are sterile, suggesting that this protein has essential functions in mammalian reproduction. There, however, are no published reports on the localization of spdya mRNA in the germline or in somatic cell lineages within the gonads from mollusks or other invertebrate species. Using a previously obtained transcriptome assembly from the scallop Argopecten purpuratus, an economically important hermaphroditic scallop species from Chile and Peru, there was identification of a complete coding sequence of the spdya mRNA. Phylogenetically spdya protein has sequence conservation homology with other scallops and mollusks. The relative mRNA transcript abundances at different gametogenic stages was assessed using quantitative PCR procedures. Results indicated there was an increase of spdya mRNA transcript abundance in testicular region samples at the late active stage, followed by a decrease in testis of reproductively mature individuals. To gain insight into the cellular localization of ap-spdya transcript within the gonads, specific RNA probes were synthesized for in situ hybridization analyses of gonad histological sections. Results indicated spdya mRNA is located exclusively in early germline (previtellogenic oocytes and spermatogonia) and somatic proliferative tissues of A. purpuratus ovarian and testicular regions. Overall, these results indicate there are putative functions of spdya in the early oogenesis and spermatogenesis of A. purpuratus and will contribute to furthering the understanding of gametogenesis in this species.

Environmental variability and larval supply to wild and cultured shellfish populations

Coastal upwelling ecosystems support some of the most productive fisheries of the planet together with a large shellfish aquaculture sector that depends on oceanographic processes to deliver planktonic larvae to replenish and feed the farmed stock. Coastal shellfish aquaculture operations in Chile and Perú have experienced large interannual fluctuations in larval supply over the past decade, yet the drivers of such variability remain unidentified. We focused on the effects of environmental variability on larval supply of the farmed Peruvian bay scallop Argopecten purpuratus in a bay in northern Chile (Tongoy Bay, 30∘S) that accounts for over 90% of countrywide landings. We examined the hypothesis that the environmental processes governing larval supply were shared with wild benthic invertebrates with planktonic larval development and compared time series of larval abundance for the scallop with larval supply rates to benthic populations of two well-studied wild intertidal species: the Chthamalid barnacle Jehlius cirratus and the purple mussel Perumytilus purpuratus. To this end, we examined the cross-correlation of larval supply to environmental variability using MODIS satellite fields of sea surface temperature (SST) chlorophyll-a concentration (chl-a) and fluorescence line height (nFLH), together with three climate indices relevant for the south east Pacific sector: the Southern Oscillation index (SOI), the Pacific Decadal Oscillation (PDO) and the Antarctic Oscillation Index (AAO). Our results showed that over the five-year study period (2009–2013), patterns of larval supply to the scallop population were related to inter-annual variability in the environmental processes as captured by their Empirical Orthogonal Functions (EOFs), likely to adult condition before spawning. Surprisingly, larval supply for none of the wild species showed a clear association to the EOFs. In contrast, scallops and wild species showed significant association to lower frequency climate variability as captured by the SOI and the PDO, but not the AAO. Results suggest that larval supply patterns to Tongoy Bay may be modulated by regional patterns of climatic variability, particularly of tropical origin. Thus, changes in coastal oceanography associated with ongoing changes in global climate could have strong and lasting effects on the supply of seedstock for wild and cultivated species across this eastern boundary coastal system and argue for the establishment of long-term ocean observing and early warning systems along the region.

Big defensin from the scallop Argopecten purpuratus ApBD1 is an antimicrobial peptide which entraps bacteria through nanonets formation

Big defensins is a large family of antimicrobial peptides found in restricted groups of invertebrates, in particular mollusks where they have highly diversified. Big defensins are composed of a highly hydrophobic N-terminal region and a C-terminal region containing six cysteine residues whose arrangement is identical to that of vertebrate β-defensins. They have been shown to be active against both Gram-positive and Gram-negative bacteria and fungi. Antimicrobial aggregates called nanonets entrapping and killing bacteria have been recently described for the hydrophobic N-terminal region of the Cg-BigDef1 from the oyster Crassostrea gigas. To determine whether nanonets formation is a conserved trait of mollusk big defensins, we assessed the potential entrapping of bacteria through nanonets of the big defensin from the scallop Argopecten purpuratus, ApBD1. Recombinant ApBD1 was produced with a thrombin-cleavable N-terminal His6 tag, followed by the mature peptide carrying a mutation of the last cysteine residue of the C-terminal region by and arginine, named rApBD1(C87R). This mutation did not apparently affect the three-dimensional structure and the biological properties of rApBD1(C87R), as evidenced by in silico modeling and in vitro antimicrobial assays. Strong immune staining of rApBD1(C87R) in numerous areas surrounding bacteria was observed by confocal microscopy, suggesting that rApBD1(C87R) entraps bacteria in peptide aggregates similar to those reported to the oyster big defensin. This study suggests the conservation of bactericidal activity and nanonet formation across big defensins from bivalve mollusks.

Evaluation of bacterial strains to improve the productivity of microalgae used in bivalve hatcheries in Peru

AbstractThe microalgae Isochrysis galbana and Chaetoceros gracilis are part of the basic diet of most bivalve cultures. This study evaluated the supplementation of bacterial strains naturally associated with these microalgae to improve their productivity. Ten bacterial strains collected from I. galbana and C. gracilis commercial cultures used in the larviculture of the Peruvian scallop Argopecten purpuratus were isolated and purified. These strains were individually coinoculated to each microalgal culture to confirm their promoter effect on growth. First, inoculation was carried out in a volume of 500 mL with constant aeration, which allowed the selection of the best bacterial strains. Then, the culture growth performance after transfer from 500 mL to 2 L tanks, with and without bacterial reinoculation during transfer, was monitored. Two bacterial strains, Lysinibacillus fusiformis and Bacillus cereus, significantly improved (α = .05) I. galbana production, whereas three other strains, Lysinibacillus sp., Psychrobacter celer, and Staphylococcus saprophyticus, significantly increased (α = .05) the growth of the C. gracilis culture. The use of microalgae supplemented with bacteria did not significantly affect A. purpuratus larval rearing. Altogether, these results showed the potential of native probiotic bacteria to improve microalgal production within bivalve hatcheries.