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Although populations of the eastern oyster Crassostreu Virginia! have been the focus of numerous studies for more than a century, less is known about the coastal lagoon populations such as those of Delaware's Inland Bays. Increasingly, oyster restoration projects in coastal regions are incorporating oyster stocking programs to restore areas with reduced oyster populations to capture both economic benefits and ecosystem services provided by healthy reefs. In Delaware, the Center for the Inland Bays conducted a volunteer oyster gardening program lasting 20 y employing disease-resistant hatchery spat. Using a suite of microsatellite loci, we examined the genetic profiles of locally recruited inland bay oysters, nearby wild Delaware Bay oysters, and the disease-resistant hatchery strain to evaluate the potential impact of the gardening program. The Inland Bay samples showed genetic profiles similar to the wild Delaware Bay population, suggesting an extant resident population providing a consistent larval supply, potentially clouding the contribution of the hatchery-spawned gardened oysters. KEY WORDS: Crassostreu Virginia/, Delaware Inland Bays, genetic diversity, INTRODUCTION The current dogma for the conservation of biodiversity within environmental policy arose after centuries of scientific observations documenting the landscape impacts of exploitation, habitat degradation, and increasing human activity [...]

The eastern oyster, Crassostrea virginica, has been an important fishery species in the United States for hundreds of years. The emergence of population devastating diseases such as MSX and Dermo was met with the development of disease-resistant lines. Although selectively bred oysters have shown improved survival and growth under diseases in the field, it is unknown if long-term selection has altered larval fitness. In this study, the larval fitness of a selected line (DBX) was studied and compared with that of the Delaware Bay wild (Wild) population under hatchery and natural conditions with the latter using untreated seawater, 50% feeding, and declining salinity. No difference in growth was observed between DBX and Wild larvae under either condition, but DBX exhibited a higher survival under hatchery conditions (P = 0.090), whereas the Wild performed equally well under both conditions. Under natural conditions, the DBX larvae had higher survival during the first week when the salinity was high, but lower survival later under low salinity. The DBX larvae had a much higher setting success and a preference for oyster shells as substrate compared with the Wild larvae. Results of this study indicate that selective breeding has unintentionally altered larval fitness of DBX and led to adaptation to hatchery and high salinity conditions with greater setting success, and the Wild larvae have wider adaptability to different conditions. These findings suggest that careful evaluation is needed to fully assess the recruitment potential of selected stocks used in aquaculture and restoration. KEY WORDS: oyster, larval fitness, selected lines, domestication, aquaculture. restoration, INTRODUCTION The eastern oyster, Crassostrea virginica, has been an important fishery species in the United States for the last 250 y. The current production in the United States still cannot [...]

Simple Summary: Oysters are sessile, filter-feeding bivalves that are vital to fisheries and ecology but are poorly understood in terms of genetic diversity and distribution. This study examines small flat oysters in the Mediterranean regions of Liguria and Sardinia (Italy) using 16S rRNA sequencing to identify species. The findings reveal new insights into the Ostrea stentina complex and introduce a new species, O. neostentina, improving knowledge of Ostrea species diversity and distribution. Oysters are sessile, filter-feeding bivalve molluscs widely distributed in estuarine and coastal habitats worldwide. They constitute a valuable resource for fisheries and extensive aquaculture and provide essential ecological services. Yet, their genetic diversity and distribution remain understudied. The variability in shell morphology complicates species classification, which is influenced by environmental and genetic factors. Although molecular phylogenetics research has refined oyster taxonomy and identified approximately 100 extant species, numerous taxonomic uncertainties persist. In the present study, we aimed to document the occurrence of small flat oysters of the genus Ostrea along the Mediterranean coastal areas of Liguria and Sardinia (Italy). Specifically, 16S rRNA sequence data were used to identify Ostrea species. Our findings offer novel insights into the O. stentina species complex and O. neostentina, a new species in the Mediterranean coastal areas of Italy. The study data further our understanding of Ostrea species diversity, distribution, and evolutionary patterns. [ABSTRACT FROM AUTHOR]

The taxonomy of Saceostrea oysters is problematic because of their highly variable shells. Molecular studies have revealed diverse sequence lineages that do not correspond to valid species names including some Saceostrea mordax-like oysters. The S. mordax-like oysters (n = 202) were collected from southern China and classified into three lineages, A, B, and C, based on both shell morphology and mitochondrial 16S rihosomal RNA (I6S) and cytochrome oxidase I (COT) sequences. Molecular and morphological analyses indicate lineages A and B are S. mordax, and lineage C is a new species Saceostrea mordoides sp. nov. The shell morphology of the new species is variable, as in other Saceostrea oysters, but distinctive in that shell height is similar to shell length with the right valve much smaller than the left valve and having undulate laminae. The average Kimura's two-parameter distance between S. mordoides sp. nov. and other Saceostrea oysters is 0.046-0.120 for 16S and 0.106-0.240 for COI, which are significantly higher than typical distances among closely related oyster species. This study shows that S. mordoides is a new species different from S. mordax, highlighting rich species diversity of Saceostrea oysters and the need for molecular taxonomy. KEY WORDS: oyster taxonomy, molecular phylogeny, 16S rihosomal RNA, cytochrome oxidase I, Saceostrea mordax, Saceostrea mordoides. Ostreidae, INTRODUCTION Oysters are highly variable in shell morphology. Different authors identified species based on different ecotypes and created considerable confusion in oyster classification (Harry 1985, Guo et al. 2018). Among [...]

Small flat oysters of the genus Ostrea were collected from China, Japan, and the United States for identification and phylogenetic analysis. Fragments of mitochondrial cytochrome oxidase subunit I and 16S rRNA genes were sequenced in 57 specimens. Shell morphology and phylogenetic analyses identified four closely related groups in the Ostrea stentina/equestris/aupouria species complex, supporting recent and ongoing speciation. Groups 1 and 2 are both O. equestris (Say, 1834), representing two divergent populations from the Asian Pacific and the Americas, respectively. Groups 3 and 4 are two separate species independent of O. equestris. Group 4 is O. stentina occurring in northern Spain, Portugal, Morocco, and northern Tunisia. Group 3 is a new species Ostrea neostentina sp. nov. found in southeastern Spain, eastern Tunisia, Hong Kong, and Japan. The occurrence of O. equestris in both Atlantic and Pacific oceans, from Argentina, Columbia, the United States, Gulf of California, Japan, and China to New Zealand, is unusual and highlights wide connectivity of Ostrea species as part of the marine ecosystem. This study provides the first record of O. equestris and O. neostentina sp. nov. along the southern coast of China and adds to the understanding of the diversity, global distribution, and evolution of Ostrea species. KEY WORDS: oyster classification, evolution, phylogenetics, COI, Ostrea stentina, Ostrea equestris, Ostreidae, Bivalvia, Ostrea neostentina, INTRODUCTION Oysters are widely distributed in world oceans and estuaries. They are important fishery resources and important ecological service providers (Beck et al. 2011). Oysters support important aquaculture industries worldwide [...]

Genome assembly can be challenging for species that are characterized by high amounts of polymorphism, heterozygosity, and large effective population sizes. High levels of heterozygosity can result in genome mis‐assemblies and a larger than expected genome size due to the haplotig versions of a single locus being assembled as separate loci. Here, we describe the first chromosome‐level genome for the eastern oyster, Crassostrea virginica. Publicly released and annotated in 2017, the assembly has a scaffold N50 of 54 mb and is over 97.3% complete based on BUSCO analysis. The genome assembly for the eastern oyster is a critical resource for foundational research into molluscan adaptation to a changing environment and for selective breeding for the aquaculture industry. Subsequent resequencing data suggested the presence of haplotigs in the original assembly, and we developed a post hoc method to break up chimeric contigs and mask haplotigs in published heterozygous genomes and evaluated improvements to the accuracy of downstream analysis. Masking haplotigs had a large impact on SNP discovery and estimates of nucleotide diversity and had more subtle and nuanced effects on estimates of heterozygosity, population structure analysis, and outlier detection. We show that haplotig masking can be a powerful tool for improving genomic inference, and we present an open, reproducible resource for the masking of haplotigs in any published genome. [ABSTRACT FROM AUTHOR]

ABSTRACT Although oysters are important aquaculture and fishery species as well as keystone species in coastal and estuarine ecology, their global species diversity is not fully understood due to problems [...]

ABSTRACT Oyster classification is problematic because of variations in shell morphology, and the use of molecular data may help to confirm species identity and clarify taxonomic confusion. Two ostreid oysters [...]