International Journal of Marine Science, 2025, Vol.15, No.1, 15-27 http://www.aquapublisher.com/index.php/ijms 21 differentiation with Japanese populations (Qi et al., 2017). The reasons for this differentiation may include changes in the paleomarine environment (such as the Taiwan Strait was exposed during the last ice age, thus isolating the north-south population) and the restrictions on the north-to-north transmission of juveniles in the current East China Sea and Yellow Sea circulation pattern. 5.2 Population connectivity and management of oysters along the Eastern Atlantic coast of North America The eastern oyster (Crassostrea virginica) along the Atlantic coast of North America is distributed from the vast coastal zone between the Gulf of Canada and the Gulf of Mexico. It is the cornerstone species of local coastal ecological and fishery resources. The genetic connectivity pattern of its population is deeply affected by coastline topography and hydrological conditions. It can be summarized as: the Atlantic coast and the Gulf Coast are relatively independent, while the coastal interior shows a certain gradient change. RAD markers and genome-wide studies consistently show that there is a dividing line between the genetic structure of the eastern oysters near the Florida Peninsula. The Atlantic coastal populations and the Gulf of Mexico populations allele frequencies were significantly different at multiple nuclear loci, with F_ST reaching above 0.05, showing significant genetic differentiation. Inside each side, the eastern oyster population is generally higher in connectivity but with regional gradients and estuary effects. Along the Atlantic coast, from New England, Chesapeake Bay to the northeastern coast of Florida, the gene flow is continuously distributed, but due to the long coastline, genetic differences between populations will rise slightly with the increase of distance, which is the classic "isolation distance-by-distance" model. As the largest estuary bay on the east coast of the United States, Chesapeake Bay also has certain differences between its internal oyster subgroup and its offshore coast (Hornick and Plough, 2021). Based on these pattern characteristics, North America adopted a strategy of regional partitioning and localized recovery for the management of oyster resources in the eastern region. Due to the obvious differences in ethnic groups in the Atlantic and Gulf of Mexico, managers usually avoid transporting oyster seedlings across these two regions to avoid potentially undermining the adaptive balance of the local gene bank. Disease control and genetic breeding are also key points in management (Proestou et al., 2016). Eastern oysters are susceptible to MSX and Dermo diseases, and for this purpose, disease-resistant strains have been cultivated and used for breeding and recovery. However, it should be noted that artificial breeding may reduce population genetic diversity. Therefore, when large-scale release of disease-resistant seedlings, the management department will supervise their genetic composition to avoid excessive proportion of single-class families. 5.3 Isolation and recovery potential of rock oyster populations in Europe and the Southern Hemisphere The native oysters along the coast and southern hemispheres mostly belong to the genus Flat Oyster and the genus Rock Oyster. Their populations often experience a severe decline after historical over-catching. They are currently mainly isolated populations, but they also show certain recovery potential and management value. European native oysters were once widely distributed in coastal waters from Norway, the United Kingdom to the Mediterranean, forming a large number of oyster beds (Figure 2). However, since the late 19th century, European flat oysters have become functionally extinct in many sea areas due to factors such as over-digging and disease. Currently, there are only a few sporadic wild populations, such as Loch Ryan in Scotland, the west coast of Sweden with colder water temperatures, and the local Gulf areas in France, Spain and other places. These surviving populations are limited in size, far apart from each other, and are basically in genetic isolation (Monteiro et al., 2024). In view of the extreme recession of European flat oysters, countries are currently actively advancing their recovery plans. For example, Germany piloted the deployment of artificially bred young oysters in the North Sea to rebuild reef beds; the United Kingdom, the Netherlands and others established the "Native Oyster Restoration Alliance" (NORA) to coordinate international cooperation. These recovery projects emphasize two aspects in genetic management: one is to use local legacy oysters as parents as possible to preserve regional unique genotypes; the other is to maintain a high number of parents and balanced family contributions during the
RkJQdWJsaXNoZXIy MjQ4ODYzNA==