Korean coastal waters mark the southern distribution limit of Pacific cod (Gadus macrocephalus) in the northwestern Pacific, where climate regime shifts (CRSs) since the late 1980s have driven regional variability in cod catches. Despite the species' ecological and commercial importance, limited research has explored how temperature-dependent physiological traits during early life stages (ELSs; eggs and larvae) interact with local oceanographic conditions to influence recruitment success. This study experimentally assessed cod ELS survival and growth across temperatures representative of Korean spawning seasons and applied these results to estimate a habitat suitability index (HSI: 0-1) across three regions, namely the eastern, western, and southern coasts of Korea, over multiple decades. Hatching rates declined sharply below 3 °C and above 10 °C (HSI < 0.6), while larval survival increased at lower temperatures. Along the eastern coast of Korea, persistent stratification and bottom cooling maintained favourable ELS conditions (HSI ≥ 0.6), coinciding with steadily rising catches. In the western coast of Korea, catches declined in the late 1980s despite favourable spawning conditions, likely due to unfavourable larval-stage environments (HSI < 0.6), which improved following the re-expansion of the Yellow Sea Bottom Cold Water. In the southern coast of Korea, broader warming rendered most areas unsuitable for ELS survival, but Jinhae Bay maintained favourable conditions (HSI ≥ 0.6) due to cold-bottom inflow via the Korea Strait. These findings advance our understanding of climate-driven shifts in cod ELS habitats and provide a theoretical basis for predicting regional recruitment dynamics and informing adaptive fishery management.

Located within the subpolar front (SPF) zone, the eastern coast of Korea is subject to frequent environmental changes on both spatial and temporal scales. In this study, we analyzed seasonal changes in the algal community structure and related environmental factors at two sites, Chodo (CD) and Sageunjin (SG), which were influenced by cold and warm-water masses, respectively, in the SPF zone. Sea surface temperature (SST) exhibited greater seasonal change in CD, whereas significant wave height was higher in SG. The salinity and nutrient concentrations decreased during summer and increased in winter at both sites. Seasonal shifts in the dominant species were distinct, with turf species positively correlated with SST dominating the intertidal zone of SG during winter, and canopy species were associated with nutrient concentrations dominating the intertidal zone of CD. Bryopsidales, which was positively correlated with the N:P ratio, dominated the SG subtidal zone in summer, whereas Fucales, which was positively correlated with the SST, dominated the CD subtidal zone. These results enhance our understanding of seaweed responses to environmental changes in SPF zones and provide a basis for predicting future changes in coastal ecosystems.

Typhoons disturb the upper ocean, weaken the physical stratification, and induce temporal and spatial changes in primary production, which rapidly alter the distribution and diversity of fishery resources. This study analyzed the response of oceanic conditions and fishery resources on the sea area of the typhoon pathway in the East/Japan Sea (Type A: typhoon passed from southwest to northeast; Type B: typhoon dissipated in the southwest; Type C: typhoon passed from southeast to northeast; and Type D: typhoons passed from southwest to northwest). For Types A and B, the sea surface temperature (SST) decreased in all areas, and Chl-a showed the largest fluctuations in the southwest. For Type C, the SST variation was reduced in the eastern part, stratification was strengthened, and Chl-a did not differ significantly in each area. For Type D, SST and Chl-a showed significant variations in the western part. The biomass of fishery resources increased along the typhoon path for each type, and the diversity increased for Types A and D but decreased for Type B; however, the diversity and catch of fishery resources increased in the northeast for Type C. This study contributes to understanding the impact of typhoon pathway changes on the marine environment and ecosystem.

The eastern coasts of Korea (ECK) and Japan (ECJ) are located at the southernmost limit of walleye pollock distribution in the Northwest Pacific. Following the climate regime shift (CRS) in the late 1980s, pollock catches in these regions have declined sharply, with different trends emerging. This study examined the relationship between environmental factors, such as sea surface temperature (SST) and habitat suitability, and changes in pollock catches from the late 1980s to 2022. From the late 1980s to the late 1990s, El Niño and positive Pacific decadal oscillation (PDO) phases dominated, increasing SST in the ECK and ECJ habitats and rapidly decreasing catches. Although spawning grounds (SGs) have maintained high habitat suitability, nursery ground (NG) suitability has declined. From the late 1990s to 2022, La Niña and negative PDO phases prevailed, with SST continuing to rise along the ECK, further reducing catches. SG suitability remained high, but NG suitability declined. Along the ECJ, SST decreased after the late-1990s CRS, stabilizing catches. After the mid-2010s, the SST increased along the ECJ, reducing pollock catches, although SG suitability remained high. This study elucidates SST changes during early life stages and their effects on pollock catch, habitat, and resources in future marine environments.

Chum salmon (Oncorhynchus keta) exhibit a remarkable ability to adapt to changes in salinity during their life cycle. However, the fertilized egg stages are sensitive to salinity, affecting ontogeny and hatching. This study investigated the effect of salinity (0, 1, 3, and 5 PSU) on the survival of two developmental stages (<1 day after fertilization and <1 day after the eyed-egg stage) of fertilized eggs. Based on the experimental results, we assessed the spawning ground environment using the in situ salinity data of the Namdae River from 1997 to 2002, where the largest number of salmon in Korea migrate to spawn. Survival of the 6.9 PSU) with the frequency of high waves. Overall, the function of the lower river in spawning and hatching is weakening. This study enhances our understanding of the effects of climate change, including increased wave activity, on salmon spawning grounds.

Chum salmon (Oncorhynchus keta) exhibit a remarkable ability to adapt to changes in salinity during their life cycle. However, the fertilized egg stages are sensitive to salinity, affecting on-togeny and hatching. This study investigated the effect of salinity (0, 1, 3, and 5 psu) on the sur-vival of two developmental stages (< 1 day after fertilization and < 1 day after the eyed-egg stage) of fertilized eggs. Based on the experimental results, we assessed the spawning ground environ-ment of the Namdae River, where the largest number of salmon in Korea migrate to spawn. Sur-vival of the < 1 day old fertilized eggs decreased sharply at 3 psu or more, and all eggs died at 5 psu. Hatching rates of the eyed-egg stage varied depending on salinity, but hatching occurred under all environmental conditions. After 2010, the salinity of the layer of water in contact with the sediment in the lower reaches of the river tended to increase (> 6.9 psu) with the frequency of high waves. Overall, the function of the lower river in spawning and hatching is weakening. This study enhances our understanding of the effects of climate change, including increased wave ac-tivity, on salmon spawning grounds