Yellow Sea

Category: Marine and Oceanic Biomes.

Geographic Location: Asia.

Summary: This semi-enclosed sea is rich in marine life, but overfishing and pollution have caused serious concerns about the health of the sea and ensuring a sustainable future.

The Yellow Sea, located in the center of northeastern Asia, is one of the 25 major semi-enclosed seas in the world. It is surrounded by the East China Sea to the south, the Chinese landmass to the west and north, and the Korean peninsula to the east. It features two main bays, the Bohai Sea and Korea Bay.

Total surface area of the sea is 154,441 square miles (400,000 square kilometers), with a maximum length of 621 miles (1,000 kilometers) and maximum width of 435 miles (700 kilometers). The average depth of the Yellow Sea is 180–394 feet (55–120 meters), rather shallow compared to other seas in this part of the world.

The Yellow Sea contains more than 200 fish species, 140 phytoplankton species, a wide variety of zooplankton, some seabirds, and a few types of large marine mammals. In addition, aquaculture has been developed along the coasts of the sea. Yet, this unique marine system faces serious problems in maintaining sustainable development. Issues such as overfishing and pollution are continuously addressed by the three nations surrounding the sea.

Biodiversity

The Yellow Sea is rich in marine resources. As the home of more than 100 species possessing commercial value, the Yellow Sea has been intensively exploited over the years. Among 200 fish species that have been found here, 45 percent are warm-water species, 46 percent are warm-temperate forms, and 9 percent are cold-temperature species.

In addition, the long-tailed crustaceans comprise an amazing 54 species, which include 65 percent and 35 percent of warmwater and boreal forms, respectively. The cephalopod group contains 14 species, which consist of nine warm-water forms and five warm-temperate forms.

The habitats of marine populations in the Yellow Sea can be divided into two groups, near-shore and migratory. Near-shore species include those that are mainly found in bays, estuaries, and around islands, such as skate, greenline, black snapper, scaled sardine, and spotted sardine. During winter, with colder water temperatures, these species generally move to deeper waters.

The migratory species such as small yellow croaker, hairtail, and Pacific herring respond to water temperature very actively and have distinct seasonal movements. During winter, some species, such as chub mackerel, Spanish mackerel, and filefish, even migrate out of the Yellow Sea and enter the warmer East China Sea.

Reflecting the complicated oceanographic conditions of the Yellow Sea, microbial communities in the sea are fairly complex with regard to species composition, spatial distribution, and community structure. The total number of phytoplankton species is 140, including 91 diatoms, 37 dinoflagellates, seven euglenoids, four silicoflagellates, and one of cryptomonads. Composition of these species in the Yellow Sea has a distinct seasonal shift. In different seasons, different species dominate.

The overall biomass of zooplankton in the Yellow Sea is lower than that of adjacent seas; the species composition also varies with season and location. The most abundant group, copepods, accounts for 60 percent of the total species throughout the year. Zooplankton is a vital food for pelagic and demersal fish and invertebrates here.

Of marine mammals, the whales that have been observed in the Yellow Sea include the fin, humpback, and grey whale. They represent the remnant of far greater pods that used to migrate and breed here. Some marine mammals here are endangered species, including the black right whale, whitefin dolphin, Kurile harbor seal, and Japanese sea lion.

The Yellow Sea ecosystem also hosts seabirds. Two key types that breed off the eastern coast of China are the streaked shearwater (Calonectris leucomelas) and Bulwer’s petrel (Bulweria bulwerii). Among the endangered seabirds of the China coast, the relict gull (Larus relictus) and the Chinese crested tern (Sterna bernsteini) live in the Yellow Sea region. On the Korea side, of 370 bird species identified in South Korea, 112 breed in the Yellow Sea region, and 17 locations have been designated as protected breeding grounds.

Effects of Human Activity

Fisheries in the Yellow Sea represent a multinational business involving China, the Koreas, and Japan. The total catch increased to approximately 5.5 million tons (5 million metric tons) in 1984 from about 3 million tons (2.7 million metric tons) in 1970. Of this amount, only one-third to one-half is considered sustainable. The number of species that are commercially harvested is about 100, including crustaceans and cephalopods.

Demersal, or deepwater, species are the major component of the fishery resources and account for 65 to 90 percent of the annual total catch. The two most commercially important demersal species are small yellow croaker and hairtail. Because of increases in fishing effort and intensive fishing of spawning stock and young fish, catches of both species have been declining.

Overfishing has also caused serious declines in stock abundance of Pacific cod, flatfish, sea robin, red seabream, and white croaker. Surprisingly, the abundance of species such as cephalpods, skates, and daggertooth pike-congers seems to be unaffected by fishing pressure. Two possible reasons could be their scattered distribution or their strong adaptive nature.

Besides abundant natural resources, the Yellow Sea has tremendous value in terms of beautiful coastlines, aquaculture, and beaches for recreation. All coastal provinces of China along the Yellow Sea have marine aquaculture, which uses seawater to culture different species. Shangdong and Liaoning are the two provinces where the aquaculture enterprises are most advanced. Similarly, South Korea has developed its own aquaculture. In 1977, the total invertebrate mariculture produced 52 percent of the fish yield, or 280,865 tons (254,796 metric tons).

Environmental Threats

Pollution of the Yellow Sea, especially near shore, has been a serious problem for both China and South Korea. Before strict environmental laws were put into effect, both countries dumped industrial and domestic wastes directly into the sea. In addition, oil discharged from vessels, ports, and oil exploration was released into the sea.

In the western part of the Yellow Sea, where China is, more than 100 million tons (91 million metric tons) of domestic sewage and about 500 million tons (454 million metric tons) of industrial wastewater are discharged into the sea each year. The major pollutants are organic chemicals that absorb quantities of oxygen; heavy metals such as mercury, lead, and cadmium; oils; and inorganic nitrogen. On the eastern side of the Yellow Sea, the pollution level has been similar. However, due to the dynamic nature of the sea, which leads to strong and rapid mixing and biodegradation, the marine environmental quality has been measured as roughly normal. Over the past several decades, climate change—particularly the slowly rising average seawater temperature—seems to have played a role in various algal and jellyfish blooms, as well as species shifts in the overall population.

The Yellow Sea is believed to have great potential for future oil and gas exploitation in the seabed; this will produce a new challenge in maintaining the biologic health of the ecosystem. Overfishing and pollution have been the two major issues concerning the sustainable use of this precious sea up until now. Numerous agreements between nations and a great number of environmental laws and rules have been put into action. Ideally, human beings will support efforts to enforce those mandates and will add new elements to the campaign to protect the natural habitats of the Yellow Sea.

Bibliography

Choon-ho, Park, Kim Dalchoong, and Lee Seo-Huang. The Regime of the Yellow Sea: Issues and Policy Options for Cooperation in the Changing Environment. Seoul, South Korea: Institute of East and West Studies, Yonsei University, 1990.

Park, Chul. Yellow Sea and East China Sea Reported by PICES and Korean Monitoring Program. Daejeon, South Korea: Chungnam National University, 2012.

Valencia, Mark J. International Conference on the Yellow Sea, Transnational Ocean Resource Management Issues and Options for Cooperation. Honolulu, HI: East-West Environment and Policy Institute, 1987.