Oyster Survival Research Articles

EFFECTIVENESS OF REARING EQUIPMENT ON THE SURVIVAL AND GROWTH OF PEARL OYSTER (Pinctada maxima) SEED AT KODEK BAY, NORTH LOMBOK

<p><strong><em>ABSTRACT</em></strong></p> <p><em>Oyster seeds mass mortality is one of the problemes in pearl farming business. Extreme temperature changes may cause mortality in oyster seed within sehll size of 3-4 cm. Modification in rearing equipment is therefore needed to maintain oyster survival from the impact of seasonal temperature fluctuation.</em> <em>The aim of this research was to observe the effectiveness and effect of rearing equipment on the survival and growth of pearl oyster (<span style="text-decoration: underline;">Pinctada</span> <span style="text-decoration: underline;">maxima</span></em><em>) seed at Kodek Bay, North Lombok. This research conducted from March- November 2009 was the continuation from the previous observation (December 2008-February 2009). Percentage of pearl oyster seed survival reared in “tento” basket was 84%, while that in pocket was 53%. “Chi-square” test showed that pearl oyster survival rate was siginifcantly affected by using the two equipment influence within 95% confidence level with ratio of 1.00:1.06. The growth of shell width, thickness, and weight of oyster seed tended to be higher reared in a“tento” basket (having broader space for movement) than that reared in a pocket. Length-weight relationship for those treatments showed similar pattern with minor allometry (b<3). </em></p> <p><em> </em></p> <strong><em>Keywords</em></strong><em>: “Tento”basket, pocket, survival, growth, pearl oyster seed, <span style="text-decoration: underline;">Pinctada</span> <span style="text-decoration: underline;">maxima</span></em>

EFFECTIVENESS OF REARING EQUIPMENT ON THE SURVIVAL AND GROWTH OF PEARL OYSTER (Pinctada maxima) SEED AT KODEK BAY, NORTH LOMBOK

ABSTRACT Oyster seeds mass mortality is one of the problemes in pearl farming business. Extreme temperature changes may cause mortality in oyster seed within sehll size of 3-4 cm. Modification in rearing equipment is therefore needed to maintain oyster survival from the impact of seasonal temperature fluctuation. The aim of this research was to observe the effectiveness and effect of rearing equipment on the survival and growth of pearl oyster (Pinctada maxima) seed at Kodek Bay, North Lombok. This research conducted from March- November 2009 was the continuation from the previous observation (December 2008-February 2009). Percentage of pearl oyster seed survival reared in “tento” basket was 84%, while that in pocket was 53%. “Chi-square” test showed that pearl oyster survival rate was siginifcantly affected by using the two equipment influence within 95% confidence level with ratio of 1.00:1.06. The growth of shell width, thickness, and weight of oyster seed tended to be higher reared in a“tento” basket (having broader space for movement) than that reared in a pocket. Length-weight relationship for those treatments showed similar pattern with minor allometry (b<3). Keywords: “Tento”basket, pocket, survival, growth, pearl oyster seed, Pinctada maxima

Effects of Macondo Canyon 252 Oil (Naturally and Chemically Dispersed) on LarvalCrassostrea virginica(Gmelin, 1791)

ABSTRACT A series of acute and sublethal experiments were conducted to examine the potential effects of exposure to wateraccommodated fractions (WAFs) of Macondo Canyon 252 crude oil and chemically enhanced (Corexit 9500A dispersant) wateraccommodated fractions (CEWAFs) on embryogenesis, larval development, growth, and survival of the eastern oyster, Crassostrea virginica. Nominal exposure concentrations for acute experiments were 0, 100, 200, 400, 800 and 1,200 mg/L for WAFs, and 0, 6.25, 12.5, 25, 50, 100, and 200 mg/L for CEWAFs. Calculated total polycyclic aromatic hydrocarbon (TPAH) values were 0, 22.5, 45, 90, 181, and 271 µg/L for WAFs, and 0, 4.5, 8.9, 17.8, 35.7, 71, and 142 µg/L for CEWAFs. The exposure concentration for sublethal experiments was 16 mg/L CEWAF. Total polycyclic aromatic hydrocarbon concentrations represent moderate to high levels of TPAH reported during the Deepwater Horizon (DWH) event. Exposure to acute concentrations of 1 or both of these contaminants was shown to decrease fe...

Hemolymph microbiome of Pacific oysters in response to temperature, temperature stress and infection.

Microbiota provide their hosts with a range of beneficial services, including defense from external pathogens. However, host-associated microbial communities themselves can act as a source of opportunistic pathogens depending on the environment. Marine poikilotherms and their microbiota are strongly influenced by temperature, but experimental studies exploring how temperature affects the interactions between both parties are rare. To assess the effects of temperature, temperature stress and infection on diversity, composition and dynamics of the hemolymph microbiota of Pacific oysters (Crassostrea gigas), we conducted an experiment in a fully-crossed, three-factorial design, in which the temperature acclimated oysters (8 or 22 °C) were exposed to temperature stress and to experimental challenge with a virulent Vibrio sp. strain. We monitored oyster survival and repeatedly collected hemolymph of dead and alive animals to determine the microbiome composition by 16s rRNA gene amplicon pyrosequencing. We found that the microbial dynamics and composition of communities in healthy animals (including infection survivors) were significantly affected by temperature and temperature stress, but not by infection. The response was mediated by changes in the incidence and abundance of operational taxonomic units (OTUs) and accompanied by little change at higher taxonomic levels, indicating dynamic stability of the hemolymph microbiome. Dead and moribund oysters, on the contrary, displayed signs of community structure disruption, characterized by very low diversity and proliferation of few OTUs. We can therefore link short-term responses of host-associated microbial communities to abiotic and biotic factors and assess the potential feedback between microbiota dynamics and host survival during disease.

Biomarkers of dissolved oxygen stress in oysters: a tool for restoration and management efforts.

The frequency and intensity of anoxic and hypoxic events are increasing worldwide, creating stress on the organisms that inhabit affected waters. To understand the effects of low dissolved oxygen stress on oysters, hatchery-reared oysters were placed in cages and deployed along with continuously recording environmental data sondes at a reef site in Mobile Bay, AL that typically experiences low oxygen conditions. To detect and measure sublethal stress, we measured growth and survival of oysters as well as expression of three biomarkers, heat shock protein 70 (HSP70), hypoxia inducible factor (HIF) and phospho-p38 MAP kinase, in tissues from juvenile and adult oysters. Survival rates were high for both juvenile and adult oysters. Expression levels of each of the 3 isoforms of HSP 70 were negatively correlated to dissolved oxygen (DO) concentrations, suggesting that HSP 70 is useful to quantify sublethal effects of DO stress. Results for HIF and phospho-p38 MAP kinase were inconclusive. Test deployments of oysters to assess expression of HSP 70 relative to environmental conditions will be useful, in addition to measuring abiotic factors, to identify appropriate sites for restoration, particularly to capture negative effects of habitat quality on biota before lethal impacts are incurred.

Omnivory dampens trophic cascades in estuarine communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 507:197-206 (2014) - DOI: https://doi.org/10.3354/meps10815 Omnivory dampens trophic cascades in estuarine communities Keith D. Johnson1,*, Jonathan H. Grabowski2, Delbert L. Smee3 1Department of Biological Sciences, Stevenson University, 1525 Greenspring Valley Road, Stevenson, MD 21153, USA 2Marine Science Center, Northeastern University, 430 Nahant Road, Nahant, MA 01908, USA 3Department of Life Sciences, Texas A&M University - Corpus Christi, 6300 Ocean Dr., Corpus Christi, TX 78412, USA *Corresponding author: kdjohnson@stevenson.edu ABSTRACT: Predators often have large effects on prey populations and entire communities, but the nature of top-down control in speciose food webs is often difficult to assess due to consumer interactions such as complementarity, predator interference, and omnivory. To assess how top and intermediate predators affect community structure, we used predator exclusion experiments designed to isolate predator effects at different trophic levels in a species-rich community. Using oyster Crassostrea virginica reefs as a model system, predators were excluded using mesh-covered cages with openings of 1.0 cm2 (small mesh) to exclude all potential oyster predators, 5.0 cm2 (large mesh) to allow intermediate consumers but not large predators to access oyster reefs, and controls with complete predator access. Natural oyster settlement and survival were greatest in the small mesh cage when oysters were completely protected from consumers. Meanwhile, abundances of adult Panopeus herbstii, the Atlantic mud crab, an intermediate consumer and known oyster predator, were an order of magnitude greater in the large-mesh cage than in the other treatments. Oyster survival did not differ between the large-mesh cage and controls, suggesting that top predators such as blue crabs Callinectes sapidus and sheepshead Archosargus probatocephalus are likely consuming mud crabs (or inducing mud crabs to avoid controls) and consuming juvenile oysters on these oyster reefs. Top-down processes are known to be important on oyster reefs, but in this system, omnivory can overwhelm density-mediated cascading effects of top predators. We also found mud crabs to induce oysters to grow heavier shells and less soft tissue. Efforts to model the direct and indirect effects of predators on ecological communities will benefit from a more thorough understanding of the relative strength of omnivory on cascading effects of top predators. KEY WORDS: Crassostrea virginica · Indirect effects · Lethal and non-lethal effects · Mud crabs · Predator–prey interactions · Food web · Top-down Full text in pdf format PreviousNextCite this article as: Johnson KD, Grabowski JH, Smee DL (2014) Omnivory dampens trophic cascades in estuarine communities. Mar Ecol Prog Ser 507:197-206. https://doi.org/10.3354/meps10815 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 507. Online publication date: July 17, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

The Effects of a Simulated Suspended Sediment Plume on Eastern Oyster (Crassostrea virginica) Survival, Growth, and Condition

Bottom sediments are resuspended into the water column during dredging operations. These resuspended sediments are an often cited concern used to justify restrictions applied to dredging schedules in many areas of the USA. One example of a temporal restriction, commonly referred to as an environmental window, involves dredging schedules in the James River, Virginia, because of potential impacts on the eastern oyster (Crassostrea virginica Gmelin). Yet, effects’ data are lacking to understand the effects of suspended sediments to C. virginica. To address this data gap, we performed a laboratory study mimicking sediment resuspension during annual dredging operations in the James River. Field-collected oysters were exposed for 7 days under flow-through conditions to 0, 100, 250, and 500-mg/L total suspended solids (TSS) in a unique exposure system where oyster movements could be electronically monitored. Endpoints analyzed were survival, percent of time open, total number of shell movements, weight change, and condition index. Data indicated no significant effects of suspended sediment on these endpoints after 7 days of exposure. Weight change in oysters attached vertically to monitor their movements was significantly less than in oysters not monitored in every treatment. No significant differences in condition index, an indicator of oyster growth sensitive to environmental pollutants, were observed among treatments measured 30 days postexposure. Correlations performed for each treatment among monitored oyster endpoints found significant negative associations between number of movements and percent open in the 100, 250, and 500-mg/L TSS treatments and in all treatments combined. These data will help reduce the uncertainty surrounding the effects of suspended sediments on C. virginica.

Predators influence the tidal distribution of oysters (Crassostrea virginica)

Biotic and abiotic conditions can separately and synergistically influence the abundance and distribution of species and create vertical zonation patterns in marine systems. In Corpus Christi Bay, TX, USA, eastern oysters (Crassostrea virginica) are limited to intertidal habitats, while in adjacent estuaries, oysters not only grow subtidally, but thrive in these areas to the extent they are a viable commercial fishery. The purpose of this study was to assess how predators and abiotic conditions affect oyster mortality and growth at different tidal elevations. Anecdotal evidence suggests that abiotic conditions, primarily hypoxia and salinity, as well as oyster disease, limits oysters to intertidal areas. Yet, in Corpus Christi Bay, oysters are absent from subtidal areas where hypoxia is not known to occur. Infection by Perkinsus marinus (Dermo) is common in the study area, but previous work suggests that infection rates do not increase when oysters are transplanted subtidally. We investigated oyster tidal distributions by transplanting newly settled oysters into intertidal and subtidal areas. Predation on oysters was significantly greater in subtidal as compared to intertidal habitats. When protected from predators using cages, oyster survival significantly increased. Further, oysters in subtidal areas allocated significantly more resources to shell growth than did those in intertidal areas, and oysters are known to grow heavier shells in response to predators. Oyster settlement was not statistically different between inter and subtidal areas, and abiotic conditions measured during the study did not exceed known tolerance limits for oysters. Previous studies have shown that abiotic conditions influence oyster mortality and the success of restored oyster reefs. Our findings indicate that predators can also affect oyster distribution, and their effects should be evaluated when developing plans for oyster management and restoration.

Ecological condition and value of oyster reefs of the Southwest Florida shelf ecosystem

The eastern oyster Crassostrea virginica is prolific and their reefs are dominant features along the estuaries and coastal areas in the Gulf of Mexico including those along the Southwest Florida coast. This paper examines the ecological and indirect economic value of oysters and the ecosystem services they provide. Drivers of change in reefs as well as various factors (pressures) that affect oyster reefs are examined. Using the monitoring data from on-going studies, this study examined various metrics of oyster health, reproduction and survival to develop an index to create an overall state of oyster reefs in the Southwest Florida estuaries. Based on existing data, oyster reefs in Southwest Florida estuaries are at “caution”, but stable. Restoration of a more natural freshwater inflow, minimizing nutrient and contaminant input as well as decreased sedimentation will enable oyster reefs to expand and thrive.

Effects of native macroalgae and predators on survival, condition and growth of non-indigenous Pacific oysters (Crassostrea gigas)

Biological invasions by non-indigenous species are causing widespread environmental changes and can threaten biodiversity and ecosystem services. Biotic interactions can play a key role in promoting or inhibiting spread of non-indigenous species. The Pacific oyster (Crassostrea gigas Thunberg, 1793) is commonly found on intertidal shores with hard substrata, but is negatively associated with macroalgae and may be influenced by the macroalgae itself or by predators associated with it. The influence of macroalgae and predation on growth, condition and survival of juvenile Pacific oysters were tested in a field experiment at two intertidal boulder shores using hatchery-reared juvenile oysters deployed on ceramic tiles. After 10months, condition of oysters was not significantly decreased in the presence of macroalgal canopy. At one site growth was reduced by macroalgae and at the other, it tended to be enhanced, but the effect was not significant. An effect of predation could not be detected. Although spatial variation in survival and growth of juvenile oysters was found, the results suggest that pre-settlement processes and/or post-settlement processes acting upon juvenile oysters at sizes not tested in this study might better explain variation in abundance of Pacific oysters in intertidal habitats.

Assessment of Qx and Winter Mortality Disease Resistance of Mass Selected Sydney Rock Oysters, Saccostrea glomerata (Gould, 1850), in the Hawkesbury River and Merimbula Lake, NSW Australia

The Sydney rock oyster, Saccostrea glomerata, mass selection breeding program was established in 1990 in the Georges River, New South Wales, and has successfully developed lines of oysters resistant to QX disease (Marteilia sydneyi) and winter mortality disease (WM; Bonamia roughleyi). Each new generation is assessed in the Georges River, but the performance of these oysters in other estuaries affected by these diseases is unknown. To investigate the potential for genotype and environment interactions, and to assure farmers, survival and growth of progeny of the fourth-generation breeding lines developed in Georges River were assessed in two other key farming areas; the Hawkesbury River and Merimbula Lake, NSW, Australia. Hawkesbury River is affected by QX and was used to assess the QX-resistant oysters (QXr). Merimbula Lake is affected by WM, and this estuary was used to assess the WM-resistant oysters (WMr) and the dual WM and QX resistant line (WM QXr). Oysters that are QXr in the Hawkesbury River, and the WMr oysters in Merimbula Lake, had significantly lower mortality and faster growth compared with controls at the final measurement. Oysters that are QXr in the Hawkesbury River at the Marra Marra Creek and Kimmerikong Bay sites attained the 50-g "plate grade" benchmark after 24 mo of culture and had lost only 29.4% and 16.9% of oysters originally stocked, respectively. Meanwhile, QX caused losses of 93.7% and 95.7% in controls at these 2 sites, respectively. In Merimbula Lake, at the conclusion of the experiment WMr oysters were significantly heavier, were larger, and had significantly lower mortality than WM QXr and control oysters. Growth and survival of WMr, WM QXr, and QXr oysters were comparable with that measured in the Georges River.

Differences in extreme low salinity timing and duration differentially affect eastern oyster (Crassostrea virginica) size class growth and mortality in Breton Sound, LA

Understanding how different life history stages are impacted by extreme or stochastic environmental variation is critical for predicting and modeling organism population dynamics. This project examined recruitment, growth, and mortality of seed (25–75 mm) and market (>75 mm) sized oysters along a salinity gradient over two years in Breton Sound, LA. In April 2010, management responses to the Deepwater Horizon oil spill resulted in extreme low salinity (<5) at all sites through August 2010; in 2011, a 100-year Mississippi River flood event resulted in low salinity in late spring. Extended low salinity (<5) during hot summer months (>25 °C) significantly and negatively impacted oyster recruitment, survival and growth in 2010, while low salinity (<5) for a shorter period that did not extend into July (<25 °C) in 2011 had minimal impacts on oyster growth and mortality. In 2011, recruitment was limited, which may be due to a combination of low spring time salinities, high 2010 oyster mortality, minimal 2010 recruitment, cumulative effects from 10 years of declining oyster stock in the area, and poor cultch quality. In both 2010 and 2011, Perkinsus marinus infection prevalence remained low throughout the year at all sites and almost all infection intensities were light. Oyster plasma osmolality failed to match surrounding low salinity waters in 2010, while oysters appeared to osmoconform throughout 2011 indicating that the high mortality in 2010 may be due to extended valve closing and resulting starvation or asphyxiation in response to the combination of low salinity during high temperatures (>25 °C). With increasing management of our freshwater inputs to estuaries combined with predicted climate changes, how extreme events affect different life history stages is key to understanding variation in population demographics of commercially important species and predicting future populations.

Sequence Polymorphism and Expression Variability of Crassostrea gigas Immune Related Genes Discriminate Two Oyster Lines Contrasted in Term of Resistance to Summer Mortalities

Summer mortalities of Crassostrea gigas are a major concern in oyster aquaculture. They are the result of a complex interaction between the host, pathogens and environmental factors. Oyster genetics have been identified as an essential determinant of oyster susceptibility to summer mortalities. As the capability of oysters to circumvent diseases depends in part on their immune defenses, we aimed to analyze the gene expression and sequence polymorphism of 42 immune related genes in two oyster lines selected for their “High” (H) and “Low” (L) survival to summer mortalities. Results showed that the variability of gene expression and the sequence polymorphism acting on particular genes could enable the discrimination between H and L oyster lines. Besides, a higher sequence polymorphism was observed on the L line affecting 11 of the 42 analyzed genes. By analyzing gene expression, sequence polymorphism and gene copy number of two antimicrobial peptide families (Cg-Defs and Cg-Prp), and an antimicrobial protein (Cg-BPI) on individual oysters, we showed that gene expression and/or sequence polymorphism could also discriminate H and L oyster lines. Finally, we observed a positive correlation between the gene expression and the gene copy number of antimicrobials and that sequence polymorphism could be encoded in the genome. Overall, this study gives new insights in the relationship between oyster immunity and divergent phenotypes, and discusses the potential implication of antimicrobial diversity in oyster survival to summer mortalities.

The effects of environmental factors on survival, growth and biochemical composition of transplanted oysters (OstreaedulisLinnaeus, 1758) from Aegean Sea to southern Black Sea

This study examined survival, growth rate and biochemical composition of oysters (Ostrea edulis) when transplanted from Aegean Sea to southern Black Sea (Sinop) and maintained offshore in a submerged long-line from December 2008 to December 2009. In December 2009, the mean length and live weight were 92.52 ± 1.40 mm and 109.60 ± 2.41 g respectively. Mean specific growth rate (SGR) was found as 1.29 ± 0.16%. Meat yield ranged from 7.90 to 11.47%. Mean moisture and ash were 81.40 ± 0.52% and 9.50 ± 0.55% respectively. Protein content was between 36.57% and 61.31% with a mean of 50.17 ± 2.13%, while lipid content was between 4.83% and 10.86% with a mean of 7.74 ± 0.49%. Carbohydrate content was between 20.88% and 46.89% with a mean of 32.59 ± 2.38%. The study demonstrated that protein, lipid and carbohydrate were used for different metabolic needs of oysters. Mortality was dependent on physiological stress related to the gonadal activity, temperature and inorganic matter in seawater. Consequently, the low salinity rate has a negative impact on growth rate of oyster. However, there was not a serious adaptation problem in transplanted oysters from Aegean Sea to Black Sea.

Simulation of Potential Oyster Density with Variable Freshwater Inflow (1965–2000) to the Caloosahatchee River Estuary, Southwest Florida, USA

Oyster beds are disappearing worldwide through a combination of over-harvesting, diseases, and salinity alterations in the coastal zone. Sensitivity of oysters to variable discharge and salinity is particularly acute in small sub-tropical estuaries subject to regulated freshwater releases. South Florida has sub-tropical estuaries where watershed flood control sometimes results in excessive freshwater inflow to estuaries during the wet season (May-Oct) and reduced discharge and increased salinities in the dry season (Nov-Apr). The potential to reserve freshwater accumulated during the wet season could offer the capacity to regulate freshwater at different temporal scales, thus optimizing salinity conditions for estuarine biota. The goal of this study was to use simulation modeling to explore the effects of freshwater inflows and salinity on adult oyster survival in the Caloosahatchee River Estuary (CRE) in southwest Florida. Water managers derived three different freshwater inflow scenarios for the CRE based on historical and modified watershed attributes for the time period of 1965-2000. Three different salinity time series were generated from the inflow scenarios at each of three sites in the lower CRE and used to conduct nine different oyster simulations. Overall, the predicted densities of adult oysters in the upstream site were 3-4 times greater in seasons that experienced reduced freshwater inflow (e.g., increased salinity) with oyster density in the lower estuary much less influenced by the inflows. Potential storage of freshwater reduced the frequency of extreme flows in the wet season and helped to maintain minimum inflow in the dry season near the estuarine mouth. Analyses of inflows indicated that discharges ranging from 0 to 1,500cfs could promote favorable salinities of 10-25 in the lower CRE depending on wet versus dry season climatic conditions. This range of inflows is similar to that derived in other studies of the CRE and emphasizes the value of simulation models to help prescribe freshwater releases which benefit estuarine biota.

Probiotic Strains for Shellfish Aquaculture: Protection of Eastern Oyster,Crassostrea virginica, Larvae and Juveniles Againsl Bacterial Challenge

Bacterial pathogens, including several Vibrio spp. and Roseovarius crassostreae, cause severe mortality of larval and juvenile eastern oysters. The introduction of beneficial bacterial isolates in oyster hatcheries and nurseries for the biocontrol of bacterial diseases is a good alternative to the use of antibiotics. The goal of this study was to screen and characterize marine bacterial isolates as potential agents to prevent larval and juvenile mortality by the oyster pathogens Vibrio tubiashii and R. crassostreae. Screening of bacterial isolates from Rhode Island marine organisms and environment using agar-based assay methods for detection of antimicrobial activity against oyster pathogens led to the isolation of candidate probionts Phaeobacter sp. S4 and Bacillus pumilus RI06-95. Pretreatment of larval and juvenile oysters for 24 h with 102–106 cfu/mL Phaeobacter sp. S4 or B. pumilus RI06-95 protected larval oysters against mortality resulting from challenge with R. crassostreae and V. tubiashii (relative percent survival (RPS) range, 9%–56%). These probiotics also protected juvenile oysters against challenge with V. tubiashii (RPS, 37%–50%). Probiotic isolates had no negative impact on oyster survival. Protection conferred to larvae against bacterial challenge was short-lived, lasting for only 24 h after removal of the probiotics from the incubation water. These results suggest the potential of marine bacterial isolates Phaeobacter sp. S4 and B. pumilus RI06-95 to serve as biocontrol agents to reduce the impact of bacterial pathogens in the culture of Crassostrea virginica.

Influence of husbandry practices on OsHV-1 associated mortality of Pacific oysters Crassostrea gigas

In 2010 Ostreid herpesvirus-1 (OsHV-1) was detected in Australia and had a disastrous impact on Pacific oyster Crassostrea gigas aquaculture and coastal communities. The acronym POMS (Pacific Oyster Mortality Syndrome) was created in Australia to refer to mass mortalities due to OsHV-1. While management of this disease mainly involves active surveillance, rigorous biosecurity protocols and mollusc breeding programs targeting production of resistant animals, the effects of aquaculture practices on mortality outbreaks are still poorly understood. The present study aimed to determine the effect of growing heights on OsHV-1 associated mortality in C. gigas in Woolooware Bay (Australia) during the summer 2011/2012. Growing height influences the immersion time of inter-tidally cultivated oysters during each tide cycle, and could be an important risk factor for OsHV-1 exposure and mortality. Pacific oysters of different ages (2 and 12month) were placed in intertidal rearing structures at three different sites in the bay. Mortality and growth rates, infection prevalence and seawater parameters (temperature and salinity) were monitored over 7months. The outbreak started in November 2011 and mortalities were observed until late April 2012. The pattern of disease expression was time and site dependent as the mortalities started immediately after infection with OsHV-1 at two of the three sites, while the infection preceded the onset of mortality by two months at the third site. No clear difference in salinity or temperature of water was observed among sites suggesting that other environmental features influence the onset of the disease. Extreme mortalities were observed in the younger class of oysters, while the modification of growing height led to a significant increase in survival of adult oysters. Infection prevalence and intensity decreased in surviving oysters suggesting that some individuals may be able to clear the virus. Differences in mortality among sites and growing heights are discussed in relation to OsHV-1 infection intensity and prevalence in oysters, and the environmental data recorded during the outbreak.

Temperature influence on pathogen transmission and subsequent mortalities in juvenile Pacific oysters Crassostrea gigas

Since 2008, mass mortalities of 1-yr-old Crassostrea gigas associated with the ostreid herpesvirus OsHV-1 μVar have occurred along all the coasts of France when seawater temperature reaches 16 to 17°C. The present study aimed to characterize the effect of temperature on oyster survival in combination with OsHV-1 DNA quantification by standard real-time PCR and total vibrio population levels in oyster tissues. To examine the effect of seawater temperature on disease transmission and related mortality of oysters, cohabitation experiments were conducted between healthy naive oysters and oysters previously exposed to field conditions in areas where mortalities were occurring. Oysters initially maintained in controlled conditions (free of mortality and negative for OsHV-1), and then transferred to an area where high mortalities were occurring among farmed stocks, became infected with OsHV-1 and exhibited high loads of vibrios followed by significant mortalities. When previously exposed oysters were maintained indoors at 13.0°C for 40 d and then at 20.6°C, they exhibited no mortality, were negative for OsHV-1 detection, and did not transmit the disease to healthy oysters. Survival of previously exposed oysters maintained indoors at 8 temperatures ranging from 13.4 to 29.0°C varied from 25 to 48% and was negatively correlated with holding temperature. Concomitantly, survival of naive cohabiting animals (62 to 98%) decreased with increasing seawater temperature until a plateau was reached between 16.2 and 21.9°C, and increased at higher temperatures. Therefore, the optimal temperature range for disease transmission from field-exposed to naive animals was between 16.2 and 21.9°C. Our results suggest that a long-term period (40 d) at low temperature (13°C) may offer a method of mitigating mortalities in oysters that have been exposed to an infective environment.

Interactive effects of elevated temperature and CO2 levels on energy metabolism and biomineralization of marine bivalves Crassostrea virginica and Mercenaria mercenaria

The continuing increase of carbon dioxide (CO2) levels in the atmosphere leads to increases in global temperatures and partial pressure of CO2 (PCO2) in surface waters, causing ocean acidification. These changes are especially pronounced in shallow coastal and estuarine waters and are expected to significantly affect marine calcifiers including bivalves that are ecosystem engineers in estuarine and coastal communities. To elucidate potential effects of higher temperatures and PCO2 on physiology and biomineralization of marine bivalves, we exposed two bivalve species, the eastern oysters Crassostrea virginica and the hard clams Mercenaria mercenaria to different combinations of PCO2 (~400 and 800μatm) and temperatures (22 and 27°C) for 15weeks. Survival, bioenergetic traits (tissue levels of lipids, glycogen, glucose and high energy phosphates) and biomineralization parameters (mechanical properties of the shells and activity of carbonic anhydrase, CA) were determined in clams and oysters under different temperature and PCO2 regimes. Our analysis showed major inter-species differences in shell mechanical traits and bioenergetics parameters. Elevated temperature led to the depletion of tissue energy reserves indicating energy deficiency in both species and resulted in higher mortality in oysters. Interestingly, while elevated PCO2 had a small effect on the physiology and metabolism of both species, it improved survival in oysters. At the same time, a combination of high temperature and elevated PCO2 lead to a significant decrease in shell hardness in both species, suggesting major changes in their biomineralization processes. Overall, these studies show that global climate change and ocean acidification might have complex interactive effects on physiology, metabolism and biomineralization in coastal and estuarine marine bivalves.

Effects of culture media and stocking density on biofouling, shell shape, growth, and survival of the Pacific oyster (Crassostrea gigas) and the Manila clam (Venerupis philippinarum) in suspended culture

Suspended culture of bivalves offers a number of advantages over beach (intertidal) culture, but is often hindered by two issues: biofouling and suboptimal shell shape. This study assessed the efficacy of two novel culture media in Pacific oyster (Crassostrea gigas) grow-out and Manila clam (Venerupis philippinarum) nursery tray culture. We examined the combined effects of culture media type (expanded clay aggregate and lava rock), media volume (0, 15, 30, and 45Lm−2), and bivalve stocking density (226, 453, and 679indm−2 for oysters; 3019, 9057, and 15,094indm−2 for clams) on biofouling levels, shell characteristics, growth, condition, and survival of bivalves. Adding either media type to culture trays significantly reduced mussel fouling on oysters and effectively eliminated clam entanglement in mussel byssus. Clay aggregate was more effective at controlling tube worms and combined fouling on oysters than lava rock. Oyster shell shape index was not affected by either media type and decreased with increased stocking density. Oyster cup depth index decreased at higher media volumes and stocking densities, likely as a result of space restrictions. Reduced growth and condition were observed in both clams and oysters as media volume and stocking density increased. The presence of culture media slightly decreased oyster survival and improved clam survival. Oysters in all treatments exceeded minimum industry marketability standards. The benefits of culture media for biofouling control were realized at the lowest media volume (15Lm−2) suggesting that the efficacy of lower volumes of media should be assessed in the future.