Haliotis Tuberculata Research Articles

Heat hardening improves thermal tolerance in abalone, without the trade-offs associated with chronic heat exposure

Marine animals are challenged by chronically raised temperatures alongside an increased frequency of discrete, severe warming events. Exposure to repeated heat shocks could result in heat hardening, where sub-lethal exposure to thermal stress temporarily enhances thermotolerance, and may be an important mechanism by which marine species will cope with future thermal challenges. However, we have relatively little understanding of the effects of heat hardening in comparison to chronic exposure to elevated temperatures. Therefore, we compared the effects of heat hardening from repeated exposure to acute heat shocks and chronic exposure to elevated temperatures on thermal tolerance in the European abalone, Haliotis tuberculata. Adult abalones were exposed to either control temperature (15 °C), chronic warming (20 °C) or a regime of two events of repeated acute heat shock cycles (23–25 °C) during six months, and their thermal tolerance and performance, based upon cardiac activity, compared using a dynamic ramping assay. The cost associated with each treatment was also estimated via measurements of condition index (CI). Abalone exposed to both temperature treatments had higher upper thermal limits than the control, but heat-hardened individuals had significantly higher CI values, indicating an enhancement in condition status. Differences in the shape of the thermal performance curve suggest different mechanisms may be at play under different temperature exposure treatments. We conclude that heat hardening can boost thermal tolerance in this species, without performance trade-offs associated with chronic warming.

Haliotis tuberculata coccinea grow-out performances according to diet and production systems

ABSTRACT Haliotis tuberculata coccinea is a candidate of growing interest to diversify aquaculture in the Canary Islands, principally based on fish production, to improve aquaculture development opportunities. The economic viability of commercial abalone farming depends largely on the rearing system employed and the feeding sources employed during the grow-out culture period. We studied the effects of two land-based culture systems on the growth performance of abalone and the nutritional quality of their tissues, in a crossed design. Recirculated (RAS) and open flow (FLOW) culture systems were compared. Fresh macro algae (FMA) (Gracilaria cornea and Ulva rigida) were compared to manufactured compound feed (CF) and a mixture of both (MIX). Survival rates were high (97–100%) regardless the treatments tested. MIX and FMA diets produced the best results for Shell Growth Rate, Specific growth rates for shell growth (SGRsl) and weight (SGRw) as well as Food Conversion Ratio (FCR). The highest value for feed intake was recorded for the MIX diet. A positive relationship has been observed between the amounts of protein and lipids in diets and the disposition of these in the viscera of animals fed such diets. The rearing system used had no significant effect on growth and nutritional parameters.

Paralytic Shellfish Toxins in Mollusks from Galicia Analyzed by a Fast Refined AOAC 2005.06 Method: Toxicity, Toxin Profile, and Inter-Specific, Spatial, and Seasonal Variations.

Paralytic shellfish poisoning is an important concern for mollusk fisheries, aquaculture, and public health. In Galicia, NW Iberian Peninsula, such toxicity has been monitored for a long time using mouse bioassay. Therefore, little information exists about the precise toxin analogues and their possible transformations in diverse mollusk species and environments. After the change in the European PSP reference method, a refinement of the Lawrence method was developed, achieving a 75% reduction in chromatogram run time. Since the beginning of 2021, when this refinement Lawrence method was accredited under the norm UNE-EN ISO/IEC 17025, it has been used in the area to determine the toxin profiles and to estimate PSP toxicity in more than 4500 samples. In this study, we have summarized three years of monitoring results, including interspecific, seasonal, and geographical variability of PSP toxicity and toxin profile. PSP was detected in more than half of the samples analyzed (55%), but only 4.4% of the determinations were above the EU regulatory limit. GTX1,4 was the pair of STX analogs that produced the highest toxicities, but GTX2,3 was found in most samples, mainly due to the reduction of GTX1,4 but also by the higher sensitivity of the method for this pair of analogs. STX seems to be mainly a product of biotransformation from GTX2,3. The studied species (twelve bivalves and one gastropod) accumulated and transformed PSP toxins to a different extent, with most of them showing similar profiles except for Spisula solida and Haliotis tuberculata. Two seasonal peaks of toxicity were found: one in spring-early summer and another in autumn, with slightly different toxin profiles during outbreaks in relation to the toxicity during valleys. In general, both the total toxicity and toxin profiles of the southernmost locations were different from those in the northern part of the Atlantic coast and the Cantabrian Sea, but this general pattern is modified by the PSP history of some specific locations.

Genetic Insights into Biofilm Formation by a Pathogenic Strain of Vibrio harveyi.

The Vibrio genus includes bacteria widely distributed in aquatic habitats and the infections caused by these bacteria can affect a wide range of hosts. They are able to adhere to numerous surfaces, which can result in biofilm formation that helps maintain them in the environment. The involvement of the biofilm lifestyle in the virulence of Vibrio pathogens of aquatic organisms remains to be investigated. Vibrio harveyi ORM4 is a pathogen responsible for an outbreak in European abalone Haliotis tuberculata populations. In the present study, we used a dynamic biofilm culture technique coupled with laser scanning microscopy to characterize the biofilm formed by V. harveyi ORM4. We furthermore used RNA-seq analysis to examine the global changes in gene expression in biofilm cells compared to planktonic bacteria, and to identify biofilm- and virulence-related genes showing altered expression. A total of 1565 genes were differentially expressed, including genes associated with motility, polysaccharide synthesis, and quorum sensing. The up-regulation of 18 genes associated with the synthesis of the type III secretion system suggests that this virulence factor is induced in V. harveyi ORM4 biofilms, providing indirect evidence of a relationship between biofilm and virulence.

Optimising abalone settlement and metamorphosis: a red macroalgae candidate as an alternative to existing algal substrates

ABSTRACT Settlement induction potential of two red algae, Sahlingia subintegra and Rhodosorus marinus, and one green macroalgae, Ulvella leptochaete was examined to identify potential alternative algal species to improve reliability and reproducibility of Haliotis tuberculata sp. settlement. CCA was used as a positive control. Settlement rates, post-larval survival and growth of Haliotis tuberculata sp. were evaluated for different algal species tested. Results showed that Sahlingia subintegra induced significantly higher settlement rates (58.17 ± 12.71%) compared to CCA, Ulvella leptochaete and Rhodosorus marinus. In all treatments, post-larvae were weekly fed a mix of diatoms (Amphora sp., and Navicula incerta). At four weeks post settlement, post-larval survival rates were significantly higher on CCA and Sahlingia subintegra substrates compared to the other two algal species tested. However, at four and five weeks post settlement there were no significant differences in post-larval shell length and growth rates between CCA and Sahlingia subintegra substrates. These findings suggest that Sahlingia subintegra could be a promising alternative red macroalgae providing settlement cue for abalone hatchery stages, particularly for Haliotis tuberculata sp. and could contribute to improve abalone breeding techniques through the selection of alternative settlement substrates that could be easily managed in abalone farms environments.

From reproductive behaviour to responses to predators: Ocean acidification does not impact the behaviour of an herbivorous marine gastropod

Ocean acidification (OA), which reduces ocean pH and leads to substantial changes in seawater carbonate chemistry, may strongly impact organisms, especially those with carbonate skeletons. In marine molluscs, while the physiological effects of OA are well known, with a reduction of growth and shell calcification, there are few studies on behavioural effects. A large marine gastropod, Haliotis tuberculata, was exposed to ambient (pHT 8.0) or low pH (pHT 7.7) during a 5-month experiment. Because animal fitness can be affected through various behavioural changes, a broad spectrum of behavioural parameters was investigated, including situations involving no stress, responses to predators, righting to evaluate indirectly the level of energy reserves, and finally, reproductive behaviour. In addition, we measured the expression profile of the GABA A-like and serotonin receptor genes, often described as central neuromodulators of sensory performance and behaviour and known to be affected by OA in molluscs. No significant effect of low pH as compared to ambient pH was observed on abalone behaviour for any of these behavioural traits or gene expressions after either one week or several months of exposure to OA. The significance tests were corroborated by estimating the size of pH effects. The behaviour of this mollusc appears not to be affected by pH decrease expected by the end of the century, suggesting some resilience of the species to OA at the adult stage. This is probably related to the ecological niche of this abalone, where important pH variations can be observed at tidal, diurnal or seasonal scales.

Effect of seasonal temperature shifts on body homeostasis, biochemical parameters and chemical composition of green ormer (Haliotis tuberculata) in the Northern Adriatic.

Seasonal responses of green ormer in terms of antioxidant capacity and lipid peroxidation, proximate and fatty acid tissue composition, trace and macro elements concentrations over the seasons were studied in relation to temperature shifts in the Northern Adriatic Sea. Overall antioxidative defenses (SOD, TBARS, TAS, LDH) varied significantly (p<0.001) according to seasons (primarily spring and summer). The proportions of overall SFA were highest in summer. The proportions of MUFA increased in autumn, with significant differences between genders in spring and summer, and spring, summer and autumn for C18:1n7 and C20:4n6. The only fatty acid lacking significant variation between seasons was C22:5n3. Significant overall differences were observed in summer vs. winter samples for As, Ba, Co, Ni, Mn, Pb, Sb, and Se content in soft tissues, however, gender variations were not significant. The data obtained in the study are of utmost importance for the management of this under-investigated species.

Impact assessment of metals realeased by aluminium-based galvanic anode on the physiology of the abalone Haliotis tuberculata in controlled conditions.

To protect metal structures immersed in the sea from corrosion, the galvanic anode cathodic protection system (GACP) is often applied. However, this association leads to continuous oxidation of the galvanic anode and therefore to a release of a metal cocktail in the forms of ions or oxy-hydroxides. Therefore, the main objective of our study was to investigate the toxicity of elements released from the dissolution of an aluminium-based galvanic anode (∼95% Al, ∼5% Zn, <0.1% for In, Cu, Cd, Mn, Fe) on a grazing gastropod, the abalone Haliotis tuberculata. The present study was carried out in complement to other research currently in submission. Gastropods were exposed for 16 weeks (12 weeks of exposure and 4 weeks of decontamination phase) to 6 conditions including a control, 4 concentrations based on total aluminium level (86, 425, 1096 and 3549 µg L-1) and a trophic control, corresponding to abalones placed in non-contaminated natural seawater but fed with contaminated algae. The effects of metals on growth, glycogen levels, brix index of hemolymph, MDA levels in digestive gland and gills, hemocyte phagocytic activity, ROS production, lysosomal system and the progress of gametogenesis were investigated throughout the entire exposure allowing the realization of kinetics. The results revealed that the aluminium-based anode does not seem to have an effect on the health status of the individuals for environmentally realistic concentrations. However, in extreme conditions strong effects were reported on the growth, immune system and reproduction of abalone.

Effects on Growth of Juvenile Abalones Haliotis tuberculata Under Chronic Exposition to Metals Released from the Dissolution of an Aluminium-Based Galvanic Anode

In the marine environment, the galvanic anode cathodic protection system (GACP) undergoes oxidation and releases metals in the forms of ions or oxy-hydroxides into the environment. The objective of the present study was to investigate the toxicity of a cocktail of metals released from the dissolution of an aluminium-based galvanic anode (~ 95% Al, ~ 5% Zn) on the abalone Haliotis tuberculata. Juveniles were exposed for 16weeks (i.e. 12weeks of exposure and 4weeks of decontamination phase) and their growth, intake rate, conversion rate and metallic concentrations were monitored. A total of 6 conditions were tested: a control, 4 concentrations based on Al and a trophic control. Results showed that the mortality reached 57% for individuals exposed to 1125µg L-1 of Al, and the abalone growth significantly decreased for an Al concentration greater than 495µg L-1. At the highest exposure concentration, intake rate measurements revealed that the appetite of abalones was affected, supported by the large increase in the conversion rate which was indicative of a poor feed efficiency. The monitoring of metallic concentrations showed that H. tuberculata strongly bioconcentrated Al relative to zinc. The diet did not appear to be the primary pathway for metal entry. Concentrations that significantly impacted abalone growth and survival during the experiment were higher than those found in natural environment, but the bioconcentration of Al into the tissues of a primary consumer such as abalone may be a potential pathway for Al to enter food webs.

How Many Abalone Species Live in the Mediterranean Sea?

Morphological traits in Haliotidae may be highly variable and not consistently diagnostic for species identification, highlighting the need for an integrative approach to the taxonomy of the family, including genetic data. Four species of the genus Haliotis are currently reported for the Mediterranean Sea and the neighboring Atlantic Ocean: Haliotis tuberculata, the common European abalone with the widest Atlanto-Mediterranean range; Haliotis mykonosensis, from the Aegean, the Tyrrhenian, and the Adriatic; Haliotis stomatiaeformis, from Malta, Lampedusa, and southeastern Sicily; and the Lessepsian Haliotis pustulata, only known on the basis of few samples from the Levant. However, their taxonomic status still relies only on shell morphology. Here, sequences of two fragments of the mitochondrial molecular marker COI were obtained from 84 abalone specimens collected in the Mediterranean Sea and the neighboring Atlantic and analyzed in order to provide for the first time a genetic framework for species delimitation. This study’s results prove that H. mykonosensis is genetically identical to H. tuberculata, whereas H. stomatiaeformis is a distinct species, endemic to a restricted area of the southern Mediterranean Sea. Finally, Haliotis tuberculata coccinea from Macaronesia may deserve its status as a subspecies of H. tuberculata, with genetic signature of a limited gene flow found in specimens of the nominal subspecies (H. t. tuberculata) in both the Atlantic and the Mediterranean Sea.

Responses of early life stages of European abalone (Haliotis tuberculata) to ocean acidification after parental conditioning: Insights from a transgenerational experiment

CO2 absorption is leading to ocean acidification (OA), which is a matter of major concern for marine calcifying species. This study investigated the effects of simulated OA on the reproduction of European abalone Haliotis tuberculata and the survival of its offspring. Four-year-old abalone were exposed during reproductive season to two relevant OA scenarios, ambient pH (8.0) and low pH (7.7). After five months of exposure, abalone were induced to spawn. The gametes, larvae and juveniles were then exposed for five months to the same pH conditions as their parents. Several biological parameters involved in adult reproduction as well as in larval, post-larval and juvenile fitness were measured. No effects on gametes, fertilisation or larval oxidative stress response were detected. However, developmental abnormalities and significant decreases in shell length and calcification were observed at veliger stages. The expression profile of a GABA A receptor-like gene appeared to be regulated by pH, depending on larval stage. Larval and post-larval survival was not affected by low pH. However, a lower survival and a reduction of growth were recorded in juveniles at pH 7.7. Our results confirm that OA negatively impacts larval and juvenile fitness and suggest the absence of carry-over effects on abalone offspring. This may compromise the survival of abalone populations in the near future.

Participation of Carbohydrate Structures in the Formation of Complex Structure of Hemocyanins from Haliotis tuberculata

Glycosylation plays an important role in many important processes in organisms. Their participation in the construction of the tertiary structure and immunotherapeutic activity of the hemocyanin Rapana venosa (RvH) from the Black Sea has been presented. Based on these results, the importance of glycans in organization of the structure of hemocyanin from the abdominal mollusk Haliotis tuberculata (HtH) was also studied.&#x0D; After incubation of both isoforms HtH1 and HtH2 with yeast Saccharomyces cerevisiae and enzyme Zymolyase, fractions with lower molecular weight (MW) between 45 and 65 kDa, which corresponds to MW of functional units (FUs) of hemocyanins, was identified. A comparative analysis of 10% SDS PAGE assays confirmed the depolymerization of the subunits HtH1 and HtH2 due to the specific glycosidase in the yeast S. cerevisiae and the enzyme Zymolyase. The presented results confirm our hypothesis that glycans are involved in the formation of the structural subunits of HtH.

New insight on spatial localization and microstructures of calcite-aragonite interfaces in adult shell of Haliotis tuberculata: Investigations of wild and farmed abalones by FTIR and Raman mapping

In the present study, we investigated the shell microstructures of the gastropod European abalone Haliotis tuberculata in order to clarify the complex spatial distribution of the different mineral phases. Our studies were carried out with a standardized methodology on thirty adult European abalone H. tuberculata (5–6 cm long) composed of 15 wild individuals and 15 individuals taken from the France Haliotis hatchery. The macroscopic (binocular) and microscopic observations coupled with Fourier Transform Infrared Spectroscopy (FTIR) and Raman vibrational analysis allowed to unambiguously detect, identify and localize calcite and aragonite. For the first time it has been shown that calcite is present in 100% of farmed and wild adult shell. The microstructural details of the calcite-aragonite interfaces were revealed by using both confocal micro-Raman mapping and Scanning Electron Microscopy (SEM) observations. Calcite zones are systematically found in the spherulitic layer without direct contact with the nacreous layer. The calcite area - nacreous layer interface is made of a thin spherulitic layer with variable thickness from a few micrometers to several millimeters.In order to contribute to a better understanding of the biomineralization process, a model explaining the hierarchical arrangement of the different phases of calcium carbonate is presented and discussed. Finally, it has been shown that these calcitic zones can be connected to each other within the shells and that their spatial distributions correspond to streaks perpendicular to the direction of length growth.

Inorganic phosphate in growing calcium carbonate abalone shell suggests a shared mineral ancestral precursor

The presence of phosphate from different origins (inorganic, bioorganic) is found more and more in calcium carbonate-based biominerals. Phosphate is often described as being responsible for the stabilization of the transient amorphous calcium carbonate phase. In order to specify the composition of the mineral phase deposited at the onset of carbonated shell formation, the present study investigates, down to the nanoscale, the growing shell from the European abalone Haliotis tuberculata, using a combination of solid state nuclear magnetic resonance, scanning transmission electron microscope and spatially-resolved electron energy loss spectroscopy techniques. We show the co-occurrence of inorganic phosphate with calcium and carbonate throughout the early stages of abalone shell formation. One possible hypothesis is that this first-formed mixed mineral phase represents the vestige of a shared ancestral mineral precursor that appeared early during Evolution. In addition, our findings strengthen the idea that the final crystalline phase (calcium carbonate or phosphate) depends strongly on the nature of the mineral-associated proteins in vivo.

Constraints to effective comanagement of New Zealand's customary fisheries: experiences of the East Otago Taiāpure

Centralization of fisheries management within large-scale, colonial governing bodies can remove access and management rights of Indigenous communities and deplete marine resources through a mismatch in bioecological and managerial scales. Management of pāua (blackfoot abalone, <em>Haliotis iris</em>) in Aotearoa New Zealand exemplifies this transition from small-scale fisheries management by tangata whenua (local Indigenous people with historical claim to the land, Māori) to central government regulation and subsequent overexploitation. Comanagement strategies have the potential to address degradation of biological and cultural diversity by returning management to local scales and authority to local people. New Zealand's customary fisheries management legislation aims to facilitate such a devolution of management back to tangata whenua through the establishment of Taiāpure Local Fisheries and Mātaitai Reserves. However, local management systems can remain constrained by the wider governance structures that encompass them. These constraints are discussed in relation to a management proposal for pāua harvesting made by the East Otago Taiāpure Management Committee. The proposal aimed to return fishing practices to a customary method, providing greater protection for declining pāua populations while allowing a small harvest to continue. After a long and protracted application process, central government did not support the proposed regulation. This opposition demonstrated many of the constraints that local management committees face as they endeavor to operate within the confines of broader legal frameworks: conflicting worldviews, inequitable power sharing, perceived inferiority of Indigenous customs, requirements for conventional science, and navigation of bureaucratic processes. Insights are also drawn from another small-scale abalone fishery (ormer, <em>Haliotis tuberculata</em>) in the Channel Islands, for which the desired regulation has been in place for over three decades.

Combined effects of ocean warming and acidification on the larval stages of the European abalone Haliotis tuberculata

This study examined the physiological responses of the larval stages of Haliotis tuberculata, an economically important abalone, to combined temperature (17 °C and 19 °C) and pH (ambient pH and −0.3 units, i.e., +200% increase in seawater acidity) in a full factorial experiment. Tissue organogenesis, shell formation, and shell length significantly declined due to low pH. High temperature significantly increased the proportion of fully shelled larvae at 24 h post-fertilization (hpf), but increased the proportion of unshelled larvae at 72 hpf. Percentage of swimming larvae at 24 hpf, 72 hpf and 96 hpf significantly declined due to high temperature, but not because of low pH. Larval settlement increased under high temperature, but was not affected by low pH. Despite the fact that no interaction between temperature and pH was observed, the results provide additional evidence on the sensitivity of abalone larvae to both low pH and high temperature. This may have negative consequences for the persistence of abalone populations in natural and aquaculture environments in the near future.

The Ethyl Acetate Extract of the Marine Edible Gastropod Haliotis tuberculata coccinea: a Potential Source of Bioactive Compounds.

The phylum Mollusca represents one of the largest groups of marine invertebrates. Nowadays, molluscan shellfish belonging to the classes Bivalvia and Gastropoda are of commercial interest for fisheries and aquaculture. Although bioactive properties of bivalve molluscs have been widely investigated and several dietary supplements have been brought to the market, the bioactive potentialities of marine gastropods are poorly documented. The present study investigated the bioactive properties of tissue extracts derived from Haliotis tuberculata coccinea, or "European abalone," an edible abalone species distributed in the Mediterranean Sea and the northeast Atlantic Ocean. A bioactive organic compound-rich extract was obtained using ethyl acetate as extracting solvent. It showed antimicrobial activity towards the methicillin-resistant Staphylococcus epidermidis strain RP62A, the emerging multi-drug-resistant Stenotrophomonas maltophilia D71 and Staphylococcus aureus ATCC 6538P, being the most sensitive strain. It also showed anthelmintic activity, evaluated through the toxicity against the target model helminth Caenorhabditis elegans. In addition, the ethyl acetate extract demonstrated a selective cytotoxic activity on the cancer cell lines A375, MBA-MD 231, HeLa, and MCF7, at the concentration of 250µg/mL. The fatty acid composition of the bioactive extract was also investigated through FAME analysis. The fatty acid profile showed 45% of saturated fatty acids (SAFA), 22% of monounsaturated fatty acids (MUFA), and 33% of polyunsaturated fatty acids (PUFA). The presence of some biologically important secondary metabolites in the extract was also analysed, revealing the presence of alkaloids, terpenes, and flavonoids.

No evident effect of domestication on the anti-predator behaviour of European abalone (Haliotis tuberculata): Implications for stock enhancement programs

Stock-enhancement programs for the European abalone (Haliotis tuberculata) might be an efficient way to restore collapsed natural populations or preserve fishing activities. Specifically, this practice consists of releasing hatchery-reared juveniles from wild or farmed broodstock into natural environments. However, the process of selection and adaptation to farming conditions may result in domestication, thus leading to genetic and behavioural changes in farmed animals. Therefore, evaluating the effects of the domestication process on juveniles is a critical first step toward the development of successful abalone stock-enhancement programs. To this end, the behaviour and survival of sixteen-month-old H. tuberculata juveniles from wild and from farmed broodstock (the product of three generations of shell-length based selection) were compared. We used three assays at different spatial and temporal scales: (1) short-term responses to simulated contact with predators, (2) the activity pattern in the presence of a natural predator (the velvet crab Necora puber) in aquariums during a 2-week trial, and (3) survival in large mesocosms in the presence of predators during a 3-week trial. No significant effects of the broodstock origin of the juveniles were detected on any of the studied parameters (P > 0.05). In addition, the estimated size effects were small compared to the overall mean for most of the variables, suggesting that the domestication process was too recent to induce important behavioural changes in juveniles from farmed broodstock.Introducing crabs into the mesocosms significantly decreased abalone survival rates (P < 0.05). In the activity pattern trial, most of the abalone mortality in aquariums with crabs (55%) occurred within the first three days, which was largely attributed to initial exploration of areas outside of shelters by the abalone. In the second week, abalone spent much less time moving when crabs were present (P < 0.05).These results suggest that juveniles from both origins would likely have the same survival rates if released in the wild. The commonly reported high abalone mortality immediately after seeding is likely due to a lack of hiding behaviour or exploration of the new environment during the first few days of exposure to predators in the wild. Therefore, current release systems may need to be adjusted to the ethological characteristics of abalone juveniles to avoid high mortalities due to an initial lack of predator avoidance.

Virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata involves both quorum sensing and a type III secretion system.

Environmental Vibrio strains represent a major threat in aquaculture, but the understanding of their virulence mechanisms heavily relies on the transposition of knowledge from human-pathogen vibrios. Here, the genetic bases of the virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata were characterized. We demonstrated that luxO, encoding a major regulator of the quorum sensing system, is crucial for the virulence of this strain, and that its deletion leads to a decrease in swimming motility, biofilm formation, and exopolysaccharide production. Furthermore, the biofilm formation by V. harveyi ORM4 was increased by abalone serum, which required LuxO. The absence of LuxO in V. harveyi ORM4 yielded opposite phenotypes compared with other Vibrio species including V. campbellii (still frequently named V. harveyi). In addition, we report a full type III secretion system (T3SS) gene cluster in the V. harveyi ORM4 genome. LuxO was shown to negatively regulate the promoter activity of exsA, encoding the major regulator of the T3SS genes, and the deletion of exsA abolished the virulence of V. harveyi ORM4. These results unveil virulence mechanisms set up by this environmentally important bacterial pathogen and pave the way for a better molecular understanding of the regulation of its pathogenicity.

Acid–base balance in the hæmolymph of European abalone (Haliotis tuberculata) exposed to CO2-induced ocean acidification

Ocean acidification (OA) and the associated changes in seawater carbonate chemistry pose a threat to calcifying organisms. This is particularly serious for shelled molluscs, in which shell growth and microstructure has been shown to be highly sensitive to OA. To improve our understanding of the responses of abalone to OA, this study investigated the effects of CO2-induced ocean acidification on extra-cellular acid–base parameters in the European abalone Haliotis tuberculata. Three-year-old adult abalone were exposed for 15 days to three different pH levels (7.9, 7.7, 7.4) representing current and predicted near-future conditions. Hæmolymph pH and total alkalinity were measured at different time points during exposure and used to calculate the carbonate parameters of the extracellular fluid. Total protein content was also measured to determine whether seawater acidification influences the composition and buffer capacity of hæmolymph. Extracellular pH was maintained at seawater pH 7.7 indicating that abalones are able to buffer moderate acidification (−0.2 pH units). This was not due to an accumulation of HCO3− ions but rather to a high hæmolymph protein concentration. By contrast, hæmolymph pH was significantly decreased after 5 days of exposure to pH 7.4, indicating that abalone do not compensate for higher decreases in seawater pH. Total alkalinity and dissolved inorganic carbon were also significantly decreased after 15 days of low pH exposure. It is concluded that changes in the acid–base balance of the hæmolymph might be involved in deleterious effects recorded in adult H. tuberculata facing severe OA stress. This would impact both the ecology and aquaculture of this commercially important species.