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Human-induced climate change and ocean acidification are global environmental phenomena with a common driver: anthropogenic emissions of carbon dioxide. Both processes potentially threaten the Mediterranean bivalve mollusc aquaculture sector, which is economically relevant to several regions and countries. Detrimental effects on bivalve mollusc species might arise from the associated increase in sea surface temperature, pH reduction, higher frequency of extreme climatic events, and possible synergies with other nonclimatic stressors, such as harmful algal blooms and mollusc diseases. This paper presents the results of a questionnaire-based study of Mediterranean bivalve mollusc producers from 12 coastal regions and six countries, the latter including those with the highest production share in the Mediterranean region. This study aims to assess knowledge and perception of threat of climatic and nonclimatic environmental stressors within the Mediterranean aquaculture industry. Furthermore, it collects information about the (geographical) impacts of summer heat waves and ocean acidification. The results suggest that ocean acidification is still a relatively unknown phenomenon and generally poorly understood. Moreover, it is considered a secondary threat compared with other pressures. Summer heat waves are presently perceived as the highest threat, having been observed in a majority of the studied production sites in past years, with effects on seed (spat), adult mortality, and byssus attachment.

Filter-feeding molluscan shellfish (oysters, mussels, clams, and so forth) are grown in areas classified for sanitary quality under EU Regulation 854/2004 on the basis of Escherichia coli monitoring. Rationalizing monitoring programs through use of a single-indicator shellfish species, rather than monitoring several species, has the benefit of reducing cost. To protect public health, the indicator must show an equivalent or higher level of contamination than the species it represents. This study, using a well-established statistical method (Bland-Altman method comparison) on routine monitoring data, demonstrates that the contamination ratio between species at the same site may change across the range of contamination levels. Nevertheless, an accumulation ordering was established as follows: The common cockle Cerastoderma edule, Tapes philippinarum (Manila clam), and Mytilus spp. (mussels) are broadly equivalent, and each shows a greater level of accumulation than the oysters Crassostrea gigas (Pa...

Shell closure and restriction of filtration are behavioral responses by which bivalve molluscs can limit exposure of soft tissues to noxious or toxic agents, including harmful microalgae. In this study, we assessed the clearance rates of five species of bivalve mollusc—the northern bay scallop Argopecten irradians irradians, the eastern oyster Crassostrea virginica, the northern quahog Mercenaria mercenaria, the softshell clam Mya arenaria, and the blue mussel Mytilus edulis—exposed for one hour to each of three harmful-algal strains: Prorocentrum minimum, Alexandrium fundyense, and Heterosigma akashiwo. Clearance rates of harmful-algal cells were compared with clearance rates of a benign microalga, Rhodomonas sp., and to a Mix of each harmful alga with Rhodomonas sp. Qualitative observations of valve closure and production of biodeposits were also assessed during the exposure experiments. Feces and pseudofeces were collected and observed with light and fluorescence microscopy for the presence or...

Eosinophilic Rickettsia-like organisms (E-RLO) were found for the first time in sick oysters of the species Crassostrea gigas, grown in Laguna de San Ignacio, Baja California Sur, Mexico, in August 2014. This work presents the histological description of development of bacteria in parasitophorous vacuoles of infected cells. Confirmative diagnosis was performed by polymerase chain reaction and in situ hybridization. Bacterial growth started with eosinophilic granules (colonial), followed by the formation and growth of intracytoplasmic inclusions. The presence of E-RLO was detected in the gill epithelium, mantle, labial palps, digestive tract, and both male and female gametes. This work describes for the first time an E-RLO in C. gigas with potential vertical transmission.

Modifications in shell structure, mantle, and adductor muscle are considered derived adaptations that allowed scallops to swim. This suggests that morphological properties of the adductor muscle and shell should relate to swimming performance in scallops. Various morphological characteristics of the shell (mass, aspect ratio, and volume between the valves) and the adductor muscle (size, position, and attachment to the shell) were measured in six scallop species (Amusium balloti, Placopecten magellanicus, Equichlamys bifrons, Pecten fumatus, Mimachlamys asperrima, and Crassadoma gigantea) with distinct swimming strategies, as documented by measurements of muscle use during induced escape responses. Morphological characteristics of the shell and adductor muscle differed markedly between the species, but did not always follow their swimming strategies. Principal components analysis revealed that shell width, shell and muscle masses, and associated morphological attributes were closely linked with swimming endurance. The intensity of the escape response was best predicted by the aspect ratio and the obliqueness of the adductor muscle.

This article describes the changes in the concentration of lipids, proteins, and carbohydrates in the gonad, digestive gland, foot and mantle of Haliotis fulgens over a reproductive cycle. An average of 30 specimens was collected each month between September 2011 and August 2013 from La Bocana, Baja California Sur, Mexico. The biometrics of each specimen were recorded, and gonads were processed using a standard histological method. Additionally, from February 2012 to February 2013, portions of nonfixed organs were frozen at -54°C for use in proximal analyses. This species showed gonadal development and spawning throughout the study period, with a peak in spawning from September through February, coinciding with sea surface temperatures near 20°C and the beginning of the decline in daylight. This study demonstrates that this species utilizes proteins, lipids, and carbohydrates stored in the foot during gonadal development and that lipid levels decrease in both the digestive gland and the gonad dur...

The anatomy of the gills of aquatic gastropods has not been extensively studied, and in particular, there are few recent studies that contain ultramicroscopic images. Similarly, the literature on the anatomy of the lungs of air-breathing terrestrial snails is not voluminous. Apple snails of the genus Pomacea possess both a gill and a fully functional lung. The lung is used to breathe air and as a flotation device. This study reports on the anatomy of the gill, lung, and pneumostome of the invasive species Pomacea maculata. The gill has a structure similar to that reported in other gastropods. The gill is monopectinate and consists of numerous triangular filaments. Ciliary tracts populate the distal portions of the filaments. The filaments are primarily connective tissue, interspersed with abundant muscle bands and hemolymph sinuses. The lung is a large ovoid sac; the floor is attached to the foot of the snail and the roof of the lung underlies the mantle epithelium. The lung tissue layers consist of connective tissue and smooth muscle bundles, and hemolymph spaces are present in both the floor and roof. Cells that contain calcium granules are very abundant in the lung tissue. Patches of cilia adorn the epithelium adjacent to the central airspace. The pneumostome is a muscular structure and is heavily ciliated. The lung volume of a 50-g animal is about 6 mL. The results of this study add to the knowledge of the anatomy of respiratory organs in molluscs and show that the lung is a major site of storage of calcium.

The Yesso scallop Patinopecten yessoensis is one of the most important aquaculture species in Asian countries because of its high economic value, but it has suffered severe infection by Polydora in recent years, causing great economic losses. Polydora mainly parasitizes the left valves of the Yesso scallop, especially the region around the adductor muscle, badly damaging the shell structure and making the shell particularly fragile. To investigate the response mechanism of the Yesso scallop to Polydora, a histological study was performed on healthy and diseased Yesso scallop mantle tissues, which are thought to be responsible for shell formation. In the present study, separate histological and histochemical changes in different mantle regions were detected for the first time. In the diseased scallops, abundant mucous cells containing acid mucopolysaccharides were found in the epidermis of the outer fold, along with a great increase in cilia on the inner epidermis, and a significant increase in mucous cells secreting acid mucopolysaccharides was observed in the middle fold and the central mantle, suggesting an accelerated process of secretion and transportation of shell substances. These changes in the different mantle regions were probably responsible for the repair of different shell layers. The present study provides valuable information for the function of mantle tissue in shell formation and is helpful for genetic breeding of disease-resistant scallops in the future.

The burrowing behavior, growth, and size-dependent burrowing rates of two geoduck species—Panopea globosa and Panopea generosa—from the Mexican coast were assessed during early juvenile development (6–7 mo) using 30-L aquariums with a muddy or sandy sediment substrate. Preburial response time, digging rates, and growth were recorded monthly for organisms with an initial shell length of 5 mm (P. globosa) or 10mm (P. generosa), and continued for 6 or 7 mo. Organisms were fed Isochrysis sp. (clone T-ISO) at libitum on a daily basis during the experimental period. Digging behaviors included the inflation of the geoduck siphon, followed by expulsion of a water jet through the pedal orifice, in conjunction with coordinated muscular contractions of the foot. Both species exhibited a lag in their burial response time that was related linearly to shell length, with rates of 4.5 min/mm (P. globosa) and 3.4 min/mm (P. generosa). Burrowing rates were independent of shell length and were similar in both speci...

The objectives of this study were to determine chemical composition of the siphon and the mantle of commercialsize geoducks clams harvested in Southeast Alaska, and to measure textural differences between the two muscle tissues, comparing them with their frozen counterparts. Live geoducks were processed using standard industry practices and analyzed either fresh or after 90 days of frozen storage. The mantle significantly differed in composition and texture from the siphon. The mantle had significantly higher contents of carbohydrates and lipids, whereas the siphon had a higher moisture content. Protein content was similar between tissues, but soluble protein content in the siphon was significantly higher than in the mantle. Large differences were observed in the electrophoretic profiles of the contractile siphon, which had a greater abundance of higher molecular weight proteins than the mantle. There were also textural differences in hardness and shear energy, with the siphon presenting signific...

Two hundred sixty-one octopuses were obtained from August 2006 to June 2007 in Bahia de Los Angeles, BC, Mexico. Sizes ranged from 58–190 mm in mantle length. Diet was determined from 3 sources: the digestive tract analysis (hard rests), accumulations of hard prey remaining in refuges, and live prey present during capture. Ripe females had the greatest fullness weight index (FWI) whereas spawning/spent females had the lowest. During the spring, female and male octopuses showed the greatest FWI, whereas in summer they showed the lowest, coinciding with the spawning/spent stage. A total of 76 prey items from 8 phyla were found, with Mollusca being the most important phylum and xanthid crabs the most important prey year-round. During autumn and winter, more bivalves were consumed, whereas more crabs were consumed in spring. Males fed mainly on crabs during all gonad development stages, but spent males fed mostly on molluscs. In contrast, females fed mostly on molluscs, except ripe females, which inc...

The present study was aimed at evaluating the histochemical distribution of alkaline phosphatase (ALP), nonspecific esterase (NSE), peroxidase (POD) and various types of mucous cells in the gill, mantle and hepatopancreas of the ark shell Scapharca subcrenata. The ALP activity was found in the epithelial cells (EP) of the gill filament and the mantle as well as in the basal lamina of the glandular duct in the hepatopancreas. The staining intensity of ALP in the mantle and hepatopancreas was stronger than that in the gill. The NSE activity was detected in the EP in the gill filament, mantle and hepatopancreas, with the hepatopancreas showing a stronger intensity than the gill. The POD activity was located in the EP of the mantle and glandular duct of the hepatopancreas as well as in the connective tissue of the gill. The mantle showed stronger staining intensity of POD than the hepatopancreas. The Alcian blue (pH 2.5) periodic acid Schiff (AB-PAS) histochemical results revealed four types of mucous cells in the gill, mantle and hepatopancreas. Type III cells (nPAS+AB+) and type IV cells (aPAS+AB+) were observed in the gill, mantle and hepatopancreas. Type I cells (PAS+AB–) were not detected in the hepatopancreas but were distributed ubiquitously throughout the gill filament and mantle. Type II cells (PAS–AB+) were not detected in the gill but were distributed ubiquitously in the digestive ducts of the hepatopancreas.

Stramonita haemastoma, the southern oyster drill, is a predatory gastropod that locates prey using waterborne chemical cues. These cues move by advection and are subjected to hydrodynamic forces such as turbulence, which can have significant effects on both the delivery of cues and on the efficiency and success of organisms that use chemical cues to find prey. We investigated how flow velocity and turbulence would affect oyster drill foraging behavior in a laboratory flume, and found that oyster drills would move upstream toward exudates from fouled oyster clumps but not toward seawater controls. We then measured foraging behavior in a range of flow conditions and did not find significant differences in either foraging success or efficiency among the flow treatments. We also found that a significant number of oyster drills would continue to move upstream even if cue delivery was stopped midway through the trial. Oyster drills placed their siphon near the sediment when oyster reef exudates were delivered through the sediment, and in turbulent flows when greater momentum delivered cues to the sediment. In all flow treatments, oyster drills spent ;2.5 min motionless before proceeding upstream. Based on these observations, we posit that when first detecting an attractive cue, oyster drills evaluate the cue and flow direction using cues in the sediment and water column before making a decision to move upstream. While moving toward an attractive cue source, oyster drills will continue to move upstream even when the attractive cues are no longer being released, which allows them to find oyster reef habitats successfully in a range of flow conditions.

Changes in the number and abundance of the cohorts of jumbo squid are a demographic response associated with high variability in recruitment, and have implications for availability and accessibility to the fishing fleets. In this study, we analyzed the interannual changes in the size structure, recruitment, and sex ratio of jumbo squid Dosidicus gigas in the central Gulf of California, Mexico. Data were analyzed for the 2000 to 2009 fishing seasons (from March to November). The biological data were collected biweekly at the port of Santa Rosalia, Baja California Sur, during each fishing season. We recorded mantle length and mantle weight, and sex (male or female) was identified from morphochromatic properties of fresh gonads. We concluded that the mantle length structure of jumbo squid changed between 1 cohort and 3 cohorts from 2000 to 2009. In the study zone, the presence of 2 cohorts is common. The species shows positive allometric growth, and the females are more abundant than the males in the region. The comparison between the most important fishing grounds in the central Gulf of California (Santa Rosalia and Guaymas) showed similar patterns, such as the number of cohorts, sex ratios, growth pattern, and migration pattern identified between both coasts. We believe that this could be evidence of one population that is widely distributed in the central Gulf of California.

This is the first report on the parasites of blood cockle Anadara granosa from the Straits of Malacca. For a histopathological survey, samples were collected for 13 mo from 3 natural habitats: the west coast of Pulau Aman, Malaysia; the east coast of Banda Acheh; and the east coast of Lhokseumawe, Indonesia. After reviewing histological preparations, Nematopsis sp. was found in the connective tissue, gills, gonad, mantle, digestive glands, and foot; trematode sporocysts were identified in the gonads, stomach epithelium, mantle, digestive glands, and foot; and a turbellarian was observed in the stomach epithelium, gonads, digestive glands, mantle, and gills. Remarkable spatial differences were found in the parasitic communities of A. granosa of the Straits of Malacca; however, no apparent temporal variation in the prevalence of any parasite was evident. Nematopsis sp. infection was very common in A. granosa collected from Pulau Aman, with no clear host tissue damage. Trematode sporocysts were obse...

The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3–6 h of exposure to H. circularisquama at densities ranging from 100 to 2 × 104 cells/mL. The prevalence of damage was significantly high after 3–6 h of exposure to H. circularisquama at densities of 100 to 2 × 104 cells/mL and 5 × 103 to 2 × 104 cells/mL for trochophores and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation...

The triangle sail mussel (Hyriopsis cumingii Lea) is the most important mussel species exploited for commercial freshwater pearl production in China. However, little is known about the genes that arc involved in pearl formation. A complementary DNA library from mantle tissue of Hyriopsis cumingii was constructed to identify the genes required for pearl formation. A total of 5,019 expressed sequence tags (ESTs) were sequenced, which resulted in the identification of 620 contigs and 1,151 singletons. BLAST analysis showed that nearly half (44.7%) of these unigenes were homologous to the known genes and 55.3% were genes with unknown functions. Based on the sequence similarities, 29 genes were putatively involved in pearl formation. These EST data provide the basis for future studies of the molecular mechanisms underlying pearl formation.

The identification of hatchery-reared larvae and juveniles is fundamental to assessing the success of their release when restocking. Hatchery-reared Haliotis rubra larvae and juveniles were successfully batch-tagged with distinct and persistent marks, enabling unambiguous differentiation from wild conspecifics when recaptured. Larvae were batch-tagged with the epifluorescent dye calcein. Experiments demonstrated that the batch-tagged larval shell was clearly visible in the spire of juvenile shells after 260 days. The recapture of batch-tagged and released larvae from natural reefs after 533 days at liberty also confirmed the persistence of this tag. A reliable and cost-effective method for batch-tagging juveniles was achieved with the use of an artificial diet that resulted in a distinctive blue-green coloration of the shell. This coloration differentiated released juveniles from wild conspecifics, was easily observed with the naked eye, and persisted on the spire of individuals for 777 days at liberty. These batch-tagging protocols allow large numbers of H. rubra larvae and juveniles to be distinctly tagged for long periods of time, enabling reliable estimation of survival after release and individual growth. It is likely that these techniques could also be applied to other abalone species.

The pill clams Pisidium chilense (d'Orbigny, 1846) and Pisidium huillichum (Ituarte, 1999) showed a 2C DNA content of 4.04 ± 0.4 pg and 2.35 ± 0.24 pg, respectively. The somatic DNA content of these 2 Chilean Pisidium Pfeiffer 1821 species is within the range described previously for diploid Heterodonta, despite the fact that both showed a high chromosome number (> 100–120 chromosomes) equivalent to the polyploid level described for other species of the genus. The nuclear DNA content is shown here for the first time for species of the family Sphaeriidae. The Pisidium, like other species, are not economically important as edible species, but they play a significant role in the dynamics of nutrient and energy cycles in freshwater bodies similar to that described for other Sphaeriidae species.

We evaluated the technique of measuring the exhalant siphon area (ESA) as an indicator of feeding activity in the blue mussel, Mytilus edulis. To accomplish this, we established the relationships between ESA measured using video and image analysis and clearance rate (CR) measured simultaneously in mussels exposed to various concentrations of microalgae as a food source in the laboratory. Two size classes of mussels (30 and 60 mm shell length) were fed 6 and 7 concentrations of the unicellular alga Isochrysis galbana., respectively (0, 0.6, 1.2, 1.8, 2.4, 3.0, 6.0 mg L-1). ESA and the variation in feeding activity associated with individual mussels significantly influenced CR in 60mm mussels, whereas effects of algal concentration were not significant within the range tested. Individual variation in feeding activity significantly influenced CR in 30 mm mussels. However, unlike the 60 mm mussels, ESA did not significantly influence CR, whereas algal concentration did have a significant effect in 30...

Suspended mussel culture entails loading high densities of juvenile mussels into mesh socks, and hanging them from floating longlines, often resulting in intraspecific crowding, reduced growth, and mussel yield. Despite this potential bottleneck in culture, there are few data on behavioral mechanisms that regulate juvenile density and growth rate. A field experiment was conducted with culture socks to examine the effects of stocking density (High ∼800 mussels/30.5 cm; Low ∼400 mussels/30.5 cm), blue mussel species (Mytilus edulis and M. trossulus) and environment on early development of the culture population. In situ photography and direct sampling were used to generate time series of mussel size, valve gape, siphon area, shell orientation, and emergence in experimental socks at a commercial farm in Ship Harbour, Nova Scotia, Canada. Moored CTD-current meters and water sampling were used to characterize the sites. Emergence from the culture socks required 1–2 mo, with faster initial emergence in...

Seasonal variations in storage, partitioning, and allocation of energy reserves (proteins, carbohydrates, lipids, and triglycerides) between germinal and somatic tissues (gonad, digestive gland, mantle tissue, and adductor muscle), were investigated related to reproduction of Pacific winged pearl oyster Pteria sterna. Tissue samples were collected every three months and analyzed with histological and biochemical techniques. Energy coefficients were also calculated with data from chemical composition of tissues. Gonad samples in almost all developmental stages occurred throughout the year, suggesting that P. sterna is a multispawning species. The evidence indicates that the main reproductive season runs from January through April (21°C to 22°C) and was identified by higher frequency of ripe gonads, more and larger postvitellogenic oocytes and higher protein, lipid, and triglyceride levels in gonad tissue. Within this study period, there were two spawning peaks, July 2003 and January 2004. Gametoge...

Seasonal variations in condition index and biochemical composition of the cockle Fulvia mutica (Reeve) were studied from March 2004 to February 2005 in eastern coast of China in relation to reproductive cycle. The condition index declined during gametogenesis and spawning, recovered when the gonad was in resting phase. Histological analysis and measurements of protein, glycogen and lipid levels and RNA:DNA ratio from gonad-visceral mass, mantle, adductor muscle, and foot of F. mutica were performed. Gametogenesis took place during winter and spring at the expense of reserves (glycogen in various organs, protein in the foot, lipid in the adductor muscle), which were accumulated previously during summer and autumn. Spawning occurred in May to June when water temperature was higher and food availability was abundant. The RNA:DNA ratio is a good indicator of sexual maturity in the gonad-visceral mass; the increasing RNA:DNA ratio in the gonad-visceral mass appears to show the rising synthetic activit...

The histochemical characteristics and ultrastructure of the mantle of Gomphina veneriformis, were described using light and electron microscopy. When the mantle was distinguished into marginal, middle, and apical zones, the marginal mantle was also divided into 4-folds (inner-inner, inner-outer, middle, and outer fold), making it similar to the typical marginal mantle of Veneridae. The mantle thickness displayed a trend of reduction from the marginal zone to the apical zone. However, epidermal thickness was the thickest in the middle zone, with a thicker epidermal layer in the outer epidermis than the inner epidermis. The inner epidermis of the transitional area between the marginal and middle mantle is a simple columnar layer with well-developed microvilli on the free surface. Although the outer epidermis is also a simple columnar layer, few microvilli are present. The inner epidermis of the middle and apical zone is simple cuboidal layer, whereas the outer epidermis is a simple columnar layer. ...

Results are presented on the histology of the hypobranchial gland of the marine muricid Plicopurpura pansa (Gould 1853). The general structure and secretory features were investigated using light microscopy and histochemical methods for the determination of tryptophan/indol. The hypobranchial gland of P. pansa is an antero-posteriorly elongated organ located on the internal surface area of the mantle, that folds on its posterior side near the rectum, right of the ctenidia and anterior to the kidney. In dead animals it is easily distinguishable by the purple color that develops after removing the shell. Parallel to the hypobranchial gland, in the same position, can be found a black-pigmented structure, presumably the anal gland. The secretory epithelium, which forms the hypobranchial gland consists of at least six different and very long (156.7 μm) cell types. It was impossible to distinguish clearly the different histological regions of the hypobranchial gland, because the different cell types we...

Results of the histopathological study of mantle tissues of the commercial geoduck Panopea abbreviata hosting the nemertean Malacobdella arrokeana revealed that the normal histology of mantle tissues of the bivalve was not altered by the attachment structure of the nemertean, even when the maximum individuals per clam reached 191 nemerteans. However, the vacuum force generated by the nemertean sucker seems to elicit a slight mechanical stretching of epithelial cells and a negligible infiltration response affecting the connective tissue between inner and outer mantle epithelia beneath the point of attachment. The 99.4% bivalves examined (n ¼ 657) hosted at least 1 specimen of M. arrokeana. Adult nemerteans were able to survive outside the host for up to 3 mo at 13C. These results suggest that the relationship between M. arrokeana and P. abbreviata should be considered as a commensal rather than a parasitic relationship.