Search

Marine nitrogen (N) cycle plays important roles in controlling marine ecosystem and biogeochemistry, as it is well known as a limiting element for marine productivity and significantly influences on the carbon and phosphorus cycles in the marine environment. Also, nitrous oxide (N₂O) production via marine N cycling is regarding as climate interaction with a big concern owing to its significant warming potential in the atmosphere. The East Sea (ES) is a semi-enclosed marginal sea, but frequently referred to as a miniature ocean as it shows multiple ocean dynamic processes. Recently, a number of studies reported that the ES is rapidly changing due to anthropogenic perturbations. Given that understanding of the ES’s biogeochemical cycles under such a condition is apparently urgent, we have little knowledge about particularly N cycling and N₂O production mechanisms to date. At present, the application of metagenomics approaches is widely used for understanding marine N cycle as an important means. Here, using the information of bacterial functional genes, we for the first time investigate (1) N cycling processes and (2) N2O production pathways during June and October 2021 at three different depths (0m, 150m, and 750m) of the ES.

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.

Walleye pollock (Gadus chalcogramma) caught in the Korean fishing area dramatically decreased in the late 1980s. To investigate the potential impact of the late 1980s climate regime shift on the collapse of the pollock catch, we developed a three-dimensional hydrodynamic model with data assimilation and a particle tracking model. Data-assimilated reanalysis showed that sea surface temperature increased by approximately 2°C in the spawning area of pollock in the late 1980s. The suitable spawning area in the East Korean Bay decreased due to warming in the late 1980s. Spawned eggs of walleye pollock were tracked using a particle tracking model for 30 days in January and February during 1983–1992. The number of individuals transported to the nursery within the Korean fishing area from the spawning area was reduced by 74% in the late 1980s. The intensified East Korean Warm Current (EKWC) could be responsible for the decreased number of individuals transported to the southern area in the late 1980s. Warming in the Korean fishing area could also cause a decrease in pollock. These oceanic changes might be linked to climate regime shifts in the late 1980s. The warming regime with positive Arctic Oscillation and weakened monsoon intensified the northward flow of the EKWC and accelerated the warming of the spawning and fishing areas in the late 1980s.

Diel and gastrointestinal changes in relation to the feeding intensity and prey composition of Apogon lineatus were investigated through the analysis of the diet contents of 174 fishes collected from the southeastern coast of Korea. Fish samples were collected at both day and night times during winter using a small bottom trawl. Stomach fullness, stomach contents index (SCI) and intestine contents index (ICI) of A. lineatus varied with day-night changes. Multivariate analyses revealed that dietary contents differed significantly between the stomach and intestine, but were similar between day and night in both stomachs and intestines. In the stomachs, prey items mostly consisted of caridean shrimps and euphausiids, while the relative contributions of amphipods and unidentifiable items tended to be high in the intestine contents, indicating that the intestines mainly contained content made up of nearly digested and/or hard shell items.

Recent global climate change often leads to poleward expansions of habitat range of marine organisms in response to increasing water temperature at high latitude. This study investigated latitudinal distribution patterns of Turbo sazae from 2009 to 2018 along the southern and eastern coasts of Korea to verify whether gradual increases in seawater temperature in the East Sea/Sea of Japan (hereafter East/Japan Sea) accelerate changes in the geographic distribution of T. sazae. Between 2009 and 2018, underwater SCUBA surveys were conducted at 19 subtidal rocky shore habitats from the southern and eastern coast of the Korean Peninsula, including Jeju Island. Additionally, long-term seawater temperature records over the last 40 years (between 1980s and 2010s) from the East/Japan Sea were analyzed to verify how changes of water temperature corresponded to geographical distributions of T. sazae. The habitat range of T. sazae was found to have extended from latitude 34&deg, 02&prime, N to latitude 37&deg, 06&prime, N from 2009 to 2018. Although seawater temperature has gradually increased since the 1990s in the East/Japan Sea, habitat expansion was particularly evident during the rapid rise of coastal seawater temperature in the 2010s. Because the strong northward expansion of the Tsushima Current can accelerate the rise of seawater temperature in the East/Japan Sea, studies of the effects of climate change on marine ecosystems of the Korean Peninsula should include data from monitoring the dynamics of the Tsushima Current.

This study examined the dietary patterns of walleye pollock, Gadus chalcogrammus, off the middle eastern coast of Korea between January 2016 and December 2017 to determine the influences of various predictors on dietary changes. Based on stomach content analyses, walleye pollock was found to be a demersal carnivore that mainly consumes carid shrimps, euphausiids, mysids, teleosts, and cephalopods. The main prey species identified in the diets of walleye pollock were Euphausia pacifica (euphausiids), Themisto japonicus (amphipods), Neomysis spp. (mysids), Neocrangon communis, Pandalus borealis (carid shrimps), Watasenia scintillans (cephalopods), and Bothrocara hollandi (teleosts), which are hyper-benthic and bentho-pelagic organisms. Dietary analyses based on the weight contributions of different prey taxa to the diets revealed significant variations in dietary composition in terms of fish size, water depth, and season, implying intraspecific dietary segregation. Euphausiids dominate the diets of smaller individuals (&lt, 30 cm TL), whereas the contributions of carid shrimps, teleosts, and cephalopods increase as body size increases. Similarly, the latter three prey items are dominant food resources in deeper habitats. The PERMANOVA results revealed that the size-related spatial and temporal changes in dietary composition are all significant for the species, as well as their two- or three-way interactions among those factors, except for the size-depth interaction. The coupling effect of size and depth is indicative of depth-dependent differences in fish sizes, with the tendency for larger individuals to be distributed in deeper habitats. In addition, seasonal and interannual variations in water column structures are also evident in the diets, which may, in part, account for the diet seasonality observed in the stomach content analysis. The dietary analyses of walleye pollock will improve our understandings to seek functional role of the species in benthic food webs, and to predict the effects of environmental and anthropogenic perturbations.

Step changes to seawater temperature (SWT) in the East Asian marginal seas (EAMS) are associated with three recent climate regime shifts (CRS) occurring in the mid-1970s, late 1980s, and late 1990s, but the responses of the ocean conditions and marine ecosystems had regional differences. A step change in SWT in the East China Sea (ECS) was detected after the CRS of the 1970s as were step changes in the North Pacific Index (NPI), Pacific Decadal Oscillation Index (PDOI), and East Asian Winter Monsoon Index (EAWMI). SWT in the ECS decreased with decreasing warm water volume transport into the EAMS and a strong monsoon, but step changes in SWT in other regions were not detected as clearly. After the CRS of the 1980s, SWT in all EAMS increased rapidly with step changes detected in all five climate indices examined. These changes were associated with a weak winter monsoon, increasing surface air temperature (SAT), and increasing warm water volume transport into the EAMS. However, after the CRS of the 1990s, a decrease in SWT around the EAMS was detected in the northern part of East China Sea (NECS), and the ECS with step changes also in the EAWMI and the Arctic Oscillation Index (AOI). In contrast, SWT in the East Sea/Sea of Japan (EJS) and the Yellow Sea (YS) continuously increased during this time. Long-term changes in zooplankton biomass were affected by regional differences in the responses of atmospheric and oceanic variability to CRSs. Specifically, long-term changes in the timing of peaks in zooplankton abundances exhibited differences. During warm periods (e.g. after the 1980s CRS) in the EJS, the amount of zooplankton biomass in October increased, while in February it decreased. On the contrary, in the YS and the NECS, the peaks of October and June in zooplankton biomass occurred during cold periods (after the 1970s and 1990s CRS). Major fisheries resources also responded to the three CRSs, although warm and cold water species responded differently to changes in oceanographic conditions in regional spawning grounds.

This paper presents the relations between total length and weight for ten demersal fishes from eastern Korean waters: Alcichthys alcicornis (Steindachner 1881); Cleisthenes pinetorum Jordan et Starks, 1904; Dasycottus setiger Bean, 1890; Gadus macrocephalus Tilesius, 1810; Glyptocephalus stelleri (Schmidt, 1904); Gymnocanthus herzensteini Jordan et Starks, 1904; Gymnocanthus intermedius (Temminck et Schlegel, 1843); Liparis punctulatus (Tanaka, 1916); Lycodes tanakae Jordan et Thompson, 1914; and Pseudopleuronectes herzensteini (Jordan et Snyder, 1901). Fish samples were collected seasonally between 2011 and 2017 using bottom gill net and trammel net. The values of exponents a and b from the weight–length relations (WLRs) were estimated. The WLRs for A. alcicornis, G. herzensteini, G. intermedius, and L. punctulatus were estimated for the first time, and new maximum lengths were recorded for G. herzensteini and L. punctulatus. All the relations between total length and weight were statistically significant (all r2 > 0.937). The values of exponent b, estimated using simple linear least squares of log10-transformed weight and length data, ranged from 2.899 to 3.416.

Water temperature in the eastern part of the Yellow Sea (EYS) during winter (JFM) and summer (JJA) from 1964 to 2009 and Siberian High Pressure Index (SHI) and Arctic Oscillation index (AOI) during winter (JFM) from 1950 to 2011 were used to analyze long-term variation in oceanic and atmospheric conditions and relationship between winter and summer bottom water temperature. Winter water temperature at 0, 30 and 50 m had fluctuated highly till the late of 1980s, but after this it was relatively stable. The long-term trends in winter water temperature at both depths were separated with cold regime and warm regime on the basis of the late 1980s. Winter water temperature at 0m and 50m during warm regime increased about 0.9°C and 1.1°C respectively compared to that during cold regime. Fluctuation pattern in winter water temperature matched well with SHI and AOI The SHI had negative correlation with water temperature at 0 m (r=-0.51) and 50 m (r=-0.58). On the other hand, the AO had positive correlation with Winter water temperature at 0 m (r=0.34) and 50 m (r=0.45). Cyclic fluctuation pattern of winter water temperature had a relation with SHI and AO, in particular two to six-year periodicity were dominant from the early of the 1970s to the early of the 1980s. Before the late of 1980s, change pattern in winter water temperature at 0 and 50 m was similar with that in the bottom water temperature during summer, but after this, relationship between two variables was low.

Abnormal change in Gyeongpo beach shoreline in June of 2012 was illustrated using DGPS (Differential Global Positioning System, resolution < 0.6m) observation and drift experiment. Abrupt change in the shoreline was occurred in the latter part of June, 2012, this change was compared with that in June from 2009 to 2011. In the northern part of the beach, sand accumulated and it made beach extension and movement of the shoreline towards sea compared with that in June from 2009 to 2011. While on the other, in the southern part, the beach was eroded and it formed a steep slope around the southernmost of the beach. The shoreline in the southern part of the beach was shifted more towards land than that in the past. Change in the position of shoreline was higher in the northernmost and southernmost of the beach compared with those in the other parts. Drift in the southern part of the beach moved faster along the beach than that in the northern part of it. Key Words : DGPS, Gyeongpo beach, Shoreline, Abnormal change, Wave

Time-series change in Gyeongpo beach shoreline was illustrated using DGPS(Differential Global Positioning System, resolution < 0.6m) observation from April, 2009 to April, 2010. The shoreline was subdivided into 12 areas, and westward and eastward movement of shoreline position at each area was calculated. In general, the shoreline moved toward sea during summer, and it moved toward land during winter. The southern and northern part of the shoreline had different pattern in time-series. The shoreline in the southern part moved toward sea during summer and moved toward land during winter, but time-series pattern of the shoreline in the northern part was more complicated than that in the southern part. Pattern of time-series change in the northern part was made up of three different types; the first is that the shoreline moves continuously toward land, and the second thing is that the shoreline's movement is the opposite to the southern part, and the third thing is that the shoreline maintains a state of equilibrium without any great fluctuation. The total length of the shoreline was the largest during winter and the smallest during summer. In general, time-series change in the shoreline had positive(+) relationship with sea surface pressure and wind speed.