International Journal of Marine Science, 2025, Vol.15, No.2, 75-91 http://www.aquapublisher.com/index.php/ijms 78 plate tectonic events such as the closure of the Tethis Sea and the changes in the Indo-Pacific Strait reshape the global current pattern. For example, with Australia moving northward and New Guinea joining with Asia, the equatorial circulation was blocked, forming a pattern of separation between the modern Indian Ocean and the Pacific Ocean. The ancestor populations of the genus Spanish mackerel may be driven by changes in these currents and expand into new sea areas under the influence of the current system. Many Spanish mackerels today lay eggs nearshore and rely on ocean current diffusion to expand their habitats for the floating larval stage (Pan et al., 2020). According to research, the early life history of Spanish mackerels is drifting, and eggs and juveniles can spread hundreds of kilometers away with the surface flow. During the Pleistocene climate change, the intensity and direction of ocean currents also changed. For example, changes in prevailing winds lead to intensity adjustments such as black tides and tides, which in turn affects the distribution of fish in the northwest Pacific. Long-term fluctuations in climate modes such as Pacific Interdecadal oscillation (PDO) will cause north-south swings and changes in the upstream intensity of the current path, thereby periodically changing the connectivity of Spanish mackerel habitats (Manral et al., 2023). For example, in the cold phase of PDO, the black tide tributaries in the East China Sea in China are weak, which may reduce the mixing frequency of Spanish mackerel populations in the north and south seas; while the warm phase is the opposite. This change in marine processes is more severe in the geological age: during the last ice-interglacial transition, the current system underwent reorganization, and the South Asian monsoon and equatorial countercurrent were all changed. Therefore, as a "diffusion highway", its temporal and spatial changes directly affect the opportunity and scale of Spanish mackerel's spread across regions. Figure 1 (A) The Magellan province in southern South America showing main oceanographic circulation patterns and directionality, the extension of continental ice and the position of the coastlines during the Last Glacial Maximum (LGM). Current world coastlines shapefile and DEM raster for LGM bathymetry simulation (-150 m) from Natural Earth (public domain). Sampling localities and distribution of (B) Nacella magellanica, (C) Nacella mytilinaand (D) Nacella deaurata(Adopted from González-Wevar et al., 2023) 3.3 Fossils and ancient DNA evidence for early distribution patterns Compared with other marine fishes (such as sharks or bonefish fossils), the fossil record of Spanish mackerels is not rich because they mostly live in remote waters and their bones are not easy to preserve. However, limited fossil evidence and ancient DNA analysis still provide some clues. The suspected Spanish mackerel fossils reported mainly include vertebrae or teeth found in the Neocentric strata, but the precise ownership is still
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