International Journal of Marine Science, 2025, Vol.15, No.1, 15-27 http://www.aquapublisher.com/index.php/ijms 16 Given the ecological and economic significance of oysters, and the marked regional variation in the genetic structure and connectivity of their populations, this study aims to provide a comprehensive review of the biogeographic distribution patterns and genetic connectivity characteristics of oyster populations worldwide. It seeks to analyze the underlying drivers of these patterns and explore their implications for conservation and management. Specifically, we introduce the major oyster taxa and their global distribution status, summarize observed population differentiation across biogeographic regions, and discuss the influence of historical climatic events and ecological factors on oyster distribution and connectivity. By examining representative populations in key marine regions-such as the Northwest Pacific, the Atlantic coast of North America, Europe, and the Southern Hemisphere-we analyze case studies of genetic structure and connectivity. Finally, we assess the potential impacts of future environmental change on oyster distribution and genetic patterns, and discuss possible mitigation strategies, including genetic enhancement and adaptive evolution approaches. 2 Systematics and Global Distribution of Oysters 2.1 Taxonomic classification and representative species of major oyster groups The family Ostreidae encompasses most of the commonly recognized true oysters, also known as edible oysters. Based on morphological characteristics and molecular phylogenetic analyses, the Ostreidae can be further subdivided into several genera (or subgenera), with the most prominent groups including Crassostrea, Ostrea, Saccostrea, and the more recently proposed genus Magallana. The genus Crassostrea includes many economically important species, such as the Pacific oyster (Crassostrea gigas), the eastern oyster (C. virginica), and the Portuguese oyster (C. angulata). These species are generally characterized by their large, deep-cupped bivalve shells and typically inhabit estuarine bays, attaching to hard or muddy substrates. In contrast, the genus Ostrea consists of flat oysters, which are relatively smaller in size and possess flat, rounded shells. They often attach to rocks or shell substrates and can form low-profile, bed-like communities (Figure 1) (Richardson et al., 2022). Species in the genera Saccostrea and Striostrea, commonly referred to as rock oysters, include notable representatives such as the Sydney rock oyster (Saccostrea glomerata) from Australia and the hooded rock oyster (S. cucullata) from East Asia. These oysters are typically found in tropical and subtropical intertidal zones, residing on reef structures or mangrove roots, and are well adapted to high temperature and salinity conditions. In addition, related groups such as Isognomon and Pinctada (pearl oysters, which belong to the family Pteriidae) are also noteworthy. Some of these species can form reef-like ecological structures similar to those created by true oysters. 2.2 Global distribution regions and typical habitat environments Oysters are naturally distributed across nearly all warm coastal regions worldwide, but distinct taxonomic groups exhibit clear regional patterns of distribution across the major oceans. The Indo-West Pacific region possesses the highest global oyster species diversity, particularly in tropical and subtropical seas, where numerous species of Saccostrea and Crassostrea are found (Narasimham et al., 2007). In areas such as Southeast Asia and northern Australia, multiple Saccostrea species co-occur and can form mixed-species oyster reefs in the same intertidal zones. In contrast, the temperate North Pacific, including the coastal waters of East Asia, supports fewer native oyster species. These are primarily composed of the Pacific oyster (Crassostrea gigas) and a limited number of Saccostrea species. However, due to the extensive availability of suitable habitats, these oysters occur in large numbers and exert significant ecological influence. The native oysters of the North Atlantic region include the European flat oyster (Ostrea edulis) along European coasts and the eastern oyster (Crassostrea virginica) along the Americas. These two species have diverged into distinct genera as a result of prehistoric continental separation. In the temperate regions of the Southern Hemisphere-such as southern Australia, New Zealand, and South Africa-native oysters are mainly flat oysters and rock oysters. Historically, these regions harbored expansive oyster reef systems, but most have disappeared or exist only as remnant populations due to human impacts (Christianen et al., 2018). Despite regional differences, oysters commonly inhabit a set of typical coastal environments. Most oysters prefer shallow coastal and estuarine
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