Yellow Sea East China Sea [59] 86587_p059_078.indd 59 1/19/05 9:18:41 PM highlights ■ The Yellow Sea / East China Sea show strong infl uence of various human activities such as fi shing, mariculture, waste discharge, dumping, and habitat destruction. ■ There is strong evidence of a gradual long-term increase in the sea surface temperature since the early 1900s. ■ Given the variety of forcing factors, complicated changes in the ecosystem are anticipated. ■ Rapid change and large fl uctuations in species composition and abundance in the major fi shery have occurred. Ocean and Climate Changes [60] 86587_p059_078.indd 60 1/19/05 9:18:48 PM background The Yellow Sea and East China Sea are epi-continental seas bounded by the Korean Peninsula, mainland China, Taiwan, and the Japanese islands of Ryukyu and Kyushu. The shelf region shallower than 200m occupies more The coasts of the Yellow Sea have diverse habitats due than 70% of the entire Yellow Sea and the East China Sea. to jagged coastlines and the many islands scattered The Yellow Sea is a shallow basin with a mean depth around the shallow sea. Intertidal fl at is the most of 44 m. Its area is about 404,000 km2 if the Bohai signifi cant coastal habitat. The tidal fl at in the Yellow Sea in the north is excluded. A trough with a maximum Sea consists of several different types such as mudfl at depth of 103 m lies in the center. Water exchange is with salt marsh, sand fl at with gravel beach, sand dune slow and residence time is estimated to be 5-6 years.37 or eelgrass bed, and mixed fl at. These fl ats support A large part of the East China Sea is shelf area in the important food resources and an ecological niche for west near the continent. In the southeastern East diverse organisms, and provide feeding and wintering China Sea, however, there is the deep Okinawa Trough, and summering grounds for migratory birds. The where maximum water depth varies from greater than shallow coastal areas, encompassing more than 1,000 2000 m in its southern section to less than 1000 m islands, also show high productivity and provide good in its northeastern section. The main current driving nursery and fi shing grounds. the regional circulation is the Kuroshio and short- and These seas are known to be very productive, supplying long-term changes in the circulation are anticipated. a large portion of the protein to the populations in the surrounding nations. The primary productivity of the Yellow Sea and East China Sea has been estimated to be in the range of 150-200 mgC m-2 yr-1. Approximately 1,600 species were reported from marine and coastal habitats in the Korean Yellow Sea, including 400 phytoplankton, 300 marine macroalgae, 50 halophytes, 500 marine invertebrates, and some 389 vertebrate species.38 Among them, 166 zooplankton and 276 fi sh have been reported as resident species from the Yellow Sea Sea. Approximately 100 commercial species have been identifi ed in the region, comprising demersal China fi sh (66%), pelagic fi sh (18%), cephalopods (7%), and crustaceans (7%). East / Sea Yellow [Figure 33] Geography and bathymetry of the Yellow Sea and East China Sea [61] 86587_p059_078.indd 61 1/19/05 9:18:54 PM Ocean and Climate [Figure 34] SST anomalies at surface and 50m in February from 1967-2001 from the central Yellow Sea (top), East China Sea shelf west of Jeju Island Changes (middle), and Tsushima Current (bottom). [62] 86587_p059_078.indd 62 1/19/05 9:18:59 PM Status and Trends There has been an increase of 1.8°C in the water temperature in February in the Korean seas during the past one hundred Hydrography years.44 The increase in August water temperature was 1.0°C. The Yellow Sea/East China Sea region is where the Siberian The rate of change became greater during the past decade High and the subtropical Pacifi c Low collide, producing cold- and there has been a northward movement of isothermals dry winters and warm-wet summers. North and northwest during the period.44 SST anomalies in February indicate that winds in the autumn and winter are strong, with speeds a switch from a colder period to a warmer period occurred reaching 10 m s-1. In the spring and summer, monsoon winds circa 1983-1985 (Figure 34). The contrast with the previous reverse the direction and become weaker. Typhoons develop period was more conspicuous in the Tsushima Current region in the west subtropical Pacifi c bringing heavy rains in the than in the Yellow Sea or East China Sea shelf region. There summer and autumn. On average, about nine typhoons pass seems to be a six or seven-year time lag from the PDO. the region every year. Chemistry There are 14 rivers that drain into the Yellow and East Production of fertilizers in Korea doubled between 1975 and China seas, with a total discharge of greater than 1012 m3 1995. The annual load of phosphorus and nitrogen from the yr-1.39 The Changjiang River has the largest discharge, 895 rivers of China and Korea is estimated to be 0.9 x 109 and 100 x 109 m3 yr-1. During summer monsoon seasons when large x 109 moles respectively, which are twice as high as those precipitation occurs, salinity drops signifi cantly, sometimes reported ten years ago. The total nitrogen concentration by as much as 6 psu. Such abrupt salinity drops have off the coast of Incheon has more than doubled since the devastating effects on aquaculture and probably on the 1990s compared with that in the 1980s. While a few studies adjacent ecosystem. on the nutrient budget and transport have been made, there The surface circulation in the Yellow and East China seas are still substantial uncertainties due to huge seasonal and consists, basically, of three main currents: the Kuroshio, spatial variations. the Tsushima Current and the Yellow Sea Warm Current Concentrations of heavy metals in mussels (dry weight (YSWC). The Kuroshio enters the East China Sea through basis) from the west coast of Korea were in the same range the strait between Taiwan and Yonakunijima Island, (the as those from other coastal waters of the world oceans.45 easternmost island of the Ryukyu Islands), and fl ows But concentrations of copper and cadmium in mussels from northeastward along the shelf slope and branches into the west coast of Korea were higher than on the east and the Tsushima Strait. The YSWC fl ows into the Yellow Sea south coasts of Korea. In an extensive survey conducted after separating from the Tsushima Current in the west of in the Yellow Sea in 2000, heavy metals in the sediments, Jeju Island. There are varying opinions of the circulation seawater, fi sh tissue and organs were examined. The results systems in the Yellow Sea/East China Sea, regarding the indicate that the concentrations of most target metals were origin of Tsushima Current and YSWC.40,41,42,43 still lower than the criteria set by Europe and Korea.46 The circulation system in the Yellow Sea is rather simple Compared to trace metals, few monitoring data of synthetic in that the coastal currents fl ow southerly along both the organics were documented in Korea. By 1995 pesticide Sea Chinese and Korean coasts, while no strong and consistent production in Korea had increased by more than four current exists in the open water. The major input of warm times from that of 1970, while since 1995 the production China saline water into the basin is the YSWC through the trough has begun to decrease. PCBs in biota were surveyed in region in the center, although no consensus has been East 47 the Incheon North Harbor recently. The biota included / reached on its perennial existence. zooplankton, Pacifi c oysters, Chinese clams, shore crabs and Sea fi sh (goby). Shore crabs and goby showed very high levels of PCBs (polychlorinated biphenyls) among the biota. It seems Yellow there were PCB hot spots in this area. [63] 86587_p059_078.indd 63 1/19/05 9:19:04 PM Bivalves collected from Chunsoo Bay, which has no 38 signifi cant pollution source of PCBs and organochlorine pesticides, showed very low levels of PCBs and organochlorine 37 pesticides. 36 The level of polycyclic aromatic hydrocarbons (PAH) in mussels and oysters collected in Chunsoo Bay were very high. 35 It seems that exhaust from power plants and fi shing boats are the main sources of PAHs in this area. From the basin- 34 scale survey in 2000, the picture was not much different. Most organochlorine compounds were not detected in the 33 sediments, while those that were, such as PCBs, were still at a low level. PAHs were detected in most of the sediment 32 and fi sh tissue samples but the concentrations were lower or comparable to the level found in the other coastal oceans 31 of the world.46 120 121 122 123 124 125 126 127 128 Plankton Phytoplankton Seasonal phytoplankton blooms are [Figure 35] Distribution of phytoplankton species numbers in the known to occur but there are few time-series to show Yellow Sea, September 1992.49 the inter-annual variation in the timing and intensity of the blooms. The current limitation in the ocean color In open waters where the water column is seasonally analysis for accurate retrieval of chlorophyll delays such stratifi ed at shallow depths, bimodal seasonal blooms in data availability. Compiled in-situ records show that spring and autumn occur as expected.