Oyster populations and reef habitats have notably declined in the last century around the world. The ecological, economic, and cultural values of oysters have led to a variety of restoration efforts seeking to recover these lost benefits. Limitations of the native oyster shell substrate and the large-scale nature of many restoration projects have resulted in the increased use of a variety of alternative, or artificial, substrates to create reef structures. A text mining package was used to conduct a review of alternative substrates used for oyster restoration. Specifically, the review (1) assessed commonly used alternative substrates, (2) locations where alternative substrates are used, and (3) common performance metrics used to evaluate alternative substrates. The review demonstrated that (1) the most common substrates included porcelain, concrete, limestone, noncalcium stone, nonoyster shell, dredged shell, and engineered reefs; (2) oyster restoration with alternative substrates occurs worldwide, but evaluations of alternative substrates were primarily (79%) within the United States of America; and (3) four main categories of performance metrics are used to assess alternative substrates—biological, structural, chemical, and economic acceptability. Within the four performance metrics, however, there exists a substantial variety in terms of specific metrics used and application of metrics to assess alternative substrates. Results highlight the need for common metrics across projects to ease comparison between alternative substrate options.

The Pacific oyster Crassostrea gigas (Thunberg, 1793) is an important part of the aquaculture industry in Europe; however, since 2008, oyster mortality events (>20%) have become a regular summer occurrence. This study monitored and recorded C. gigas mortality events during a 3-y period at a commercial oyster site in Lough Foyle, North of Ireland, and related these to environmental conditions, oyster physiology, and husbandry practices. Early summer temperature rises above 16°C were consistently correlated with large mortality events, but warmer temperatures in late summer did not cause mortalities, including in 1 y when there were no early summer mortalities. Mortalities were also correlated with a sharp early summer decrease in salinity from 22.2 to 16.9. In the laboratory, the combined effects of various temperatures and salinities on oyster stress levels were investigated using total hemocyte count and neutral red retention techniques. The cell membrane integrity and hemocyte density in C. gigas are sensitive to temperatures of 20°C or greater and at salinities of 20 or lower. This suggests that high temperature and low salinity combinations can negatively impact oyster stress levels and potentially increase oyster vulnerability to infections, including oyster herpes OsHV-1 µvar. Comparing survivorship in experimental bags simulating commercial growing conditions, these results equivocally support previous studies in which higher shore position was correlated with higher survivorship. Bags of oysters at lower density in lower shore positions were equally successful and may be more protected from climate-related stressors. Focusing on a single stressor is insufficient to predict future oyster mortalities, but balancing effects and relieving stress on oyster stocks through husbandry could limit the impacts of summer mortalities.

The oceans have absorbed more than 40% of the carbon dioxide (CO₂) generated by anthropogenic activities, causing a decrease in the average pH of 0.1 units in seawater since preindustrial times. This phenomenon has been called “ocean acidification.” This change poses serious threats to the cultivation of oysters and especially to larval and spat production, activities carried out in coastal and estuarine areas, where pH levels are currently below the IPCC scenario for the year 2100 of pH = 7.8. The goal of the present work was to experimentally evaluate the effect of simulated acidification (pH 7.39 ± 0.04) on the culture in a short-term trial of Kumamoto oyster larvae Crassostrea sikamea taking the current ocean pH conditions (pH 8.116 ± 0.023) as a reference. The evaluation was carried out in an experimental system with continuous water flow and pH manipulation by CO₂ bubbling. Veliger larvae (6-day-old postspawn) were cultured at a density of six larvae mL^–1 and fed with a monoalgal diet based on Isochrysis galbana at 30,000 cells mL^–1. Mortality (%) and growth (shell length in µm) were evaluated, and damage to larval morphology (determined using scanning electron microscopy) and Ca²⁺ contents in the shells (%) were quantified by X-ray fluorescence. The results show a high sensitivity of C. sikamea veliger larvae to low pH levels with negative impacts on growth and survival, decreases in the Ca²⁺ concentrations of the shells, and the presence of morphological anomalies during the prodissoconch I stage, which were observed after the first 24 h of cultivation in experimental conditions and became progressively more evident, especially by the sixth day of culture. Acute exposure to a low pH and a saturation of aragonite (Ωar) <1 caused poor calcification in C. sikamea larvae, causing negative effects on larvae, such as shell lesions during development, smaller larvae, and higher mortality and relation to a control pH.

The Suminoe oyster Crassostrea ariakensis and the Kumamoto oyster Crassostrea sikamea coexist and are habitat-forming ecosystem engineers in the Yangtze River estuary and its adjacent coasts. To date, little quantitative information is available on the intertidal zonation patterns of these two oysters within their native range or on the related mechanisms generating these spatial patterns. This study first carried out field surveys and laboratory experiments to explore the vertical zonation patterns of the two oysters in the intertidal habitats of northern Hangzhou Bay, assess the roles of abiotic (aerial exposure stress) and biotic (larval distribution, recruitment, and competition) factors in regulating vertical zonation and understand their driving mechanisms. At the study site, C. sikamea dominated the higher intertidal zone (approximately 6.7 h and 56% emersion/12 h tidal cycle), whereas C. ariakensis occupied the three deeper intertidal zones (mid, mid-low, and low intertidal). Mean aerial exposures of 56% and 42% represented the optimal growth zones and the lower limits of C. sikamea, respectively. The growth boundary of the two oysters was located in the intertidal zone that was exposed 42% of the time. The area with the highest C. ariakensis densities (the optimal growth zone) was the mid-low intertidal (mean: 3.0 h and 25% emersion/tidal cycle). In a laboratory 72-h aerial exposure experiment, the percentage of water loss was significantly greater for C. ariakensis than for C. sikamea after 24 h (P < 0.01), which was also supported by the result that C. ariakensis had a relatively greater dry tissue weight and lower water weight of soft tissue than C. sikamea (P < 0.001). The results from the real-time quantitative PCR examining the oyster larvae abundances found that C. sikamea and C. ariakensis larvae dominated the surface and bottom layers of water, respectively. Oyster recruits were significantly more abundant in the low intertidal zone (380.2 ± 48.6 spats/400 cm²) than in the high intertidal zone (153.2 ± 45.9 spats/400 cm²) (P < 0.05), whereas the mortality of the oyster spats recruited to the experimental plates did not differ between the high and low intertidal zones (P > 0.05). Twenty-two individuals among the 30 oyster recruits (73%) in the high intertidal region were identified as C. sikamea, and six recruits (20%) were identified as C. ariakensis. All 36 recruits (100%) in the low intertidal region were identified as C. ariakensis. It was concluded that the differential larval distribution, settlement, and post-settlement mortality along the intertidal elevation gradients served as a mechanism for vertical zonation of these two oyster species.

For effective long-term restoration of depleted marine species, it is critical that populations are able to replenish themselves through reproduction. The Olympia oyster Ostrea lurida (Carpenter, 1864), the only native oyster species on the West Coast of North America, is the subject of a number of restoration efforts across its range. Information about the distribution of its early life history stages is critical for the design of effective and connected restoration networks. In this study, spawning adults (brooders), planktonic larvae, and settlers were mapped in Fidalgo Bay, Anacortes, WA, an active restoration site in the Salish Sea. Sampling was conducted weekly from May through August 2013 at five intertidal and three subtidal stations. Brooding adults, planktonic larvae, and settlers were sampled. Environmental variables measured were temperature, relative water flux (a proxy for flow), tidal height, and submersion time of traps and shell strings. A low percentage of individuals sampled were brooding (maximum 13%) throughout the sampling period, but abundance peaked in early July. Small planktonic larvae (153–243 µm) were present throughout the sampling period, but peaked in mid-July, whereas large larvae (243–333 µm) were mostly only found in mid-July. Overall, there was high variability in the distribution of larvae and settlement among various locations or depths throughout Fidalgo Bay. Planktonic larvae and settlers were much more abundant near conspecifics and at a trestle bridge that could have affected hydrodynamics and, therefore, settlement. In addition, settlement increased with increasing water flow in the intertidal, but not in the subtidal, zone. More settlement occurred at –0.3 m below mean lower low water (MLLW) than at stations above or below this elevation, indicating that postlarvae prefer to settle at an intermediate elevation band in the intertidal zone. Temperature was the most important variable measured, with an association between the increasing presence of planktonic larvae and settlement with increasing temperature. In sum, prerecruitment processes appear to be very important in determining the spatial distribution of Olympia oysters in Fidalgo Bay. These results suggest that restoration of Olympia oysters is improved by the addition of appropriate substrates in sites that contain conspecifics and are just below MLLW.

This study assessed the use of novel, locally made, protective culture cylinders as a means of improving pearl oyster Pteria penguin performance and standardizing culture methods used by mabé pearl farmers in Tonga. Cylinders were constructed from locally sourced wire mesh, for a cost of USD 12.1 each and were used to protect oysters grown on chaplets. Growth and survival of two age cohorts of oysters—“young” (0.7-y-old and 33.1 ± 0.7-mm dorsoventral height (DVH)) and “old” (2.7-y-old and 86.9 ± 0.8 mm DVH)—cultured using this system were determined every 3–5 wk over an 11-mo period. The DVH of “young” oysters increased by 74.6 mm, wet weight (WW) by 161.2 g, and shell thickness (ST) by 23.4 mm, whereas for “old” oysters, DVH, WW, and ST increased by 55.2 mm, 271.4 g, and 14.7 mm, respectively, over the same period. “Young” oysters held in culture cylinders reached the starting size of the “old” oyster cohort within seven months of growth and at less than half their age (1.2 and 2.7 y old, respectively). “Young” oysters held in culture cylinders also showed a 3-fold greater monthly growth rate than oysters cultured in trays (6.8 and 2.1 mm month^–1, respectively). Survival of oysters in culture cylinders over the 11-mo culture period was 91.7% and 97.6% for “young” and “old” oysters, respectively, compared with 25% for oysters cultured in trays. The use of protective cylinders for P. penguin culture increases oyster survival and reduces the culture period required for P. penguin to reach minimum pearl production size by >50% relative to the current tray-based culture method, supporting improved mabé pearl farm profitability.

The ribbed mussel Geukensia demissa is a mytilid bivalve that inhabits salt marshes along the east coast of North America. It is an important ecosystem engineer, contributing to salt marsh species diversity and landscape-scale ecosystem processes. Furthermore, local interest in the human consumption of G. demissa in South Carolina has created demand for this species from both restaurant and retail outlets. In response, commercial harvest of G. demissa increased markedly between 2014 and 2016. There are, however, currently no species-specific commercial or recreational harvesting regulations for G. demissa in this state, either in terms of minimum size or maximum quantity, raising concerns about the sustainability of commercial harvest, especially considering that harvesting practices can be destructive to the salt marsh ecosystem. The goal of the current study was to characterize the demographics of G. demissa at a harvested site and at two unharvested reference sites over the course of 1 y. Furthermore, the current study investigated the effects of simulated harvest on parameters of salt marsh health. Quarterly and monthly demographic sampling at commercially harvested and unharvested sites in South Carolina revealed that patches of G. demissa primarily consist of large individuals with low rates of recruitment. A similar relationship between size and age was observed at each of the sites. A year-long manipulation experiment revealed that selective harvesting practices mitigated the effect of harvest on metrics of smooth cordgrass, Spartina alterniflora health, but not on recruitment of G. demissa. The current study offers important demographic information on G. demissa in South Carolina that can be used to support future management decisions associated with its commercial and recreational fisheries.

To ensure the maintenance of natural mussel beds along the southeastern Pacific coast of Chile, it is important to understand their population dynamics. This means evaluating their genetic population structure and gene flow, and the degree of connectivity among natural beds. To do this, the spatial genetic population structure of seven natural Mytilus chilensis beds within the mussels' present distribution range along the Chilean coast was evaluated. Genetic differences were established between populations with cytochrome oxidase I (COI) gene sequences (Fst = 0.099) and microsatellites (Fst = 0.048), showing that locations that consistently presented greater differentiation were those at the extremes of the geographical distribution. An “isolation by distance” pattern was not observed in the COI and microsatellite data. We suggest that because of the high resolution of these markers, the differences between locations may be explained by high reproductive variance, which determines local changes in each reproductive cycle of the species. These changes would account for the differences between the natural beds. Furthermore, differentiated genetic types were observed in some locations, demonstrating the presence of local processes in some cases, perhaps caused by gene flow restrictions resulting from the local geomorphological and oceanographic conditions. The gene structure and connectivity of natural beds in sessile species with larval dispersion are strongly determined by local retention characteristics. For this reason, the data generated in this study can be used to improve population management. These data can also be used to support and motivate the creation of a marine protected area containing natural beds of this species with sufficient levels of genetic diversity.

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.

Advances in the optimization of abalone culture can be achieved through a deeper understanding of the molecules modulating physiological functions including growth, metabolism, and reproduction. To identify neuropeptide molecules that play key roles in the modulation, transcriptome analysis of the ganglia (e.g., cerebral and pleuropedal ganglia) of the abalone Haliotis discus hannai was performed. The long-read single-molecule real-time sequencing using the PacBio RSII platform generated 48,344 full-length transcripts, with an N50 length of 3,020 nucleotides (nt), a GC ratio of 44.76%, and a size range of 309–17,545 nt. Of these transcripts, 32,901 (68.1%), 40,515 (83.8%), 7,591 (15.7%), and 14,945 (30.9%) were annotated using the NCBI nonredundant, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Cluster of Orthologous Groups databases, respectively. Using in silico data mining, 18 putative neuropeptide genes were identified from the transcriptome of H. discus hannai. Comparative analysis revealed that the sequences of identified neuropeptides of H. discus hannai were conserved with other molluscan neuropeptide homologs; however, some features of H. discus hannai neuropeptides were found distinct from those of other molluscan neuropeptides. Interestingly, this is the first study to report a precursor encoding a DYamide peptide in molluscan, which is likely to be a homolog of DLamide peptides, which have been discovered only in annelids to date. This study provides comprehensive neuronal transcriptome data for H. discus hannai, which could help improve aquaculture methods both practically and economically by providing a basis for neuroendocrine-based strategies.

Black abalone Haliotis cracherodii Leach, 1814 are known to feed on drift plant macrodetritus moved about in the intertidal zone by waves and currents. Drift capture is a trait shared by at least several other abalone species. Drift materials are entrapped beneath the anterior foot and held for ingestion. The quantitative significance of feeding on entrapped drift macrodetritus for black abalone is unknown. Furthermore, there are no published data on the extent to which local and mesoscale spatial distributions of source plant populations influence the composition of drift plant material in black abalone diet as acquired by entrapment. From February 1982 through March 2019, occurrences of macrodetrital entrapment by black abalone were observed in nine rocky intertidal study plots, with a summed surface area of 2,054 m², on the periphery of San Nicolas Island (SNI), California (Island centroid at ∼33.25°, –119.50°). A small preliminary survey and 27 complete surveys were performed during the study period (mean of ∼1.4 y between complete surveys). During the study, more than 1.5 × 10⁵ black abalone were examined. The total likely included repeated observations of many individuals as a result of the known longevity and limited mobility of the species. Of those observed, ∼1.65 × 10³ black abalone were recorded as apparently ingesting entrapped items. Frequency data were dominated (∼95% of all records) by three species of kelp Macrocystis pyrifera (Linnaeus) C. Agardh; commonly known as “giant kelp”, Egregia menziesii (Turner), and Eisenia arborea Areschoug. Of those, giant kelp was the most frequently observed entrapped category (∼76%). Living, attached giant kelp is rarely observed in intertidal habitats at SNI, and it follows that utilization of giant kelp by black abalone requires physical importation of the kelp from other locations. Frequencies of occurrence of giant kelp entrapment by individual study site were clearly associated with the relative surface canopy sizes and persistence patterns of offshore kelp forests adjacent (≤2 km) to the respective study sites. The pattern suggests that subsidies of drift giant kelp to black abalone diet involve mesoscale physical processes largely proximate to SNI but probably not subsidies from more distant locations such as other islands or the California mainland. Utilization of other frequently recorded kelps as food by black abalone likely involves spatial subsidies as well, but on smaller scales of distance (∼10–100 m for E. arborea; ∼0–100 m for E. menziesii). In the context of the imperiled status of black abalone, recovery actions may include outplants of captive-reared animals or transplantation of wild animals from other populations. For such actions, data from SNI suggest a need for consideration of scales of separation among release locations and nearby populations of the three apparently predominant kelp species in black abalone diet.

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 effect of long-term estivation on the abundance of calcium granules in the lung tissue of the apple snail Pomacea maculata Perry was studied. Electron-dispersive spectrophotometric analysis of the shell and the granular inclusions in the lung show that both structures are composed of calcium carbonate. The layers forming the shell are similar to those found in the shells of other gastropods. Calcium granules are extremely abundant in the tissues of the lung of P. maculata. The spherical granules consist of concentric layers of material inside calcium cells. There are three distinct populations of hemocytes in P. maculata hemolymph, two cell types with granulocytic morphology and one agranular type. Selective staining shows that hemocytes contain large amounts of calcium, implicating these cells in the transport of calcium carbonate from storage sites to other tissues. The pCO₂ of the hemolymph increases in estivating gastropods, and it has been suggested that stores of solid calcium carbonate are mobilized to buffer the resulting acidity. Results of this study show that a large decrease in the abundance of calcium carbonate granules in the lung tissue occurs during estivation. In addition, there is evidence that a calcium binding protein is present in the hemocytes.

Urbanized harbors and embayments scattered along marine shorelines act as important sources of a wide range of chemical contaminants, which include metallic trace elements (MTE). Within the semi-enclosed Mediterranean Sea, the high number of such areas might locally challenge the persistence of coastal marine species. In recent decades, biomonitoring studies, using sentinel species such as mussels, have increased knowledge of coastal contamination and provided a number of contentious potential environmental surveillance biomarkers, which contributed to a better comprehension toward the acclimation abilities of marine organisms, to actual anthropogenically derived environments. The aim of this study was to characterize the influence of the chemically, multi-contaminated, Bay of Toulon (France) on the young fauna, using juvenile sea urchins Paracentrotus lividus as a proxy. Hatchery-produced individuals were immersed, for 1 mo, within the bay, at four contrasted sites for MTE concentrations. At the end of the experiment, growth and transcript abundances of key genes, involved in the acclimation process, were assessed. Contrasted phenotypic and molecular responses were observed evidencing a significant environmental influence. Specifically, under the high metallic stress, a dwarfing response was observed, associated with a high level of metallothionein and a low level of hsp response. In addition, the level of DNA methyltransferase transcript abundance was inversely correlated with the level of MTE concentrations, highlighting that the chronic exposure to metallic contaminants would probably increase the risk of genetic mutations, such as those consecutive to transpositions. Overall, this study indicates that further in-depth research into the mechanisms driving plasticity and adaptive changes at the population level is required.

Sea urchins are often used as model species in anthropogenic studies, and their aquaculture productions have expanded in recent years, yet basic rearing techniques applied in these studies vary and have received little investigation. This study assessed the effect of seawater flow rates and stocking densities on the somatic and physiological characteristics of European sea urchin species Paracentrotus lividus and Psammechinus miliaris. Two experiments were carried out for each species: one using low, medium, and high seawater flow rates (∼0.2, 0.8, and 1.60 L min^–1, respectively) and another using low, medium, and high stocking densities [∼38, 76, and 115 ind. m^–2 or 0.8, 1.6, and 2.4 kg m^–2 (wet mass), respectively]. Within the flow rate experiment, P. lividus showed no significant treatment effects. By contrast, P. miliaris reared in low seawater flow rates had significantly lower relative spine lengths and gonad indices than conspecifics reared under higher flow rates (medium and high). Within the stocking density experiment, P. miliaris reared under low stocking densities demonstrated significantly larger somatic growth (test diameter and whole animal wet mass) relative to those stocked at high densities but were similar to those stocked at medium densities. For both species, gonad indices were largest within low densities compared with those within higher stocking densities (high only for P. lividus, and medium and high for P. miliaris). This study suggests that careful consideration for general holding conditions, and comparison across anthropogenic studies is required, especially across different species. Furthermore, this information could help improve the production effort of European sea urchin species while achieving high marketable attributes.