East China Sea ecosystem

Category: Marine and Oceanic Biomes.

Geographic Location: Asia.

Summary: The East China Sea is a highly productive, temperate body in the heart of east Asian waters. Overfishing and climate change present current and future issues of concern.

The East China Sea is the major sea off the eastern coast of China; it is a marginal sea of the North Pacific Ocean. The East China Sea is bound on the west by mainland China, where the large estuary of the Yangtze River flows in at Shanghai, via Hangzhou Bay. To the south, it is bound by the Taiwan Strait (the channel to the South China Sea) and by Taiwan. To the east, the East China Sea is separated from the Philippine Sea and greater North Pacific Ocean by the arc of the Ryukyu Islands chain, and to the northeast by Kyushu, southernmost of Japan's “big four” main islands. Directly north lies the Korea Strait (channel to the Sea of Japan), the South Korean island of Jeju, and the Yellow Sea.

The East China Sea is most often considered as including the Yellow Sea, which is tantamount to a large gulf opening off its northwest, between mainland China and the Korean Peninsula. The total area of the sea is about 482,000 square miles (1.25 million square kilometers). In addition to the Yangtze, about 40 other large rivers flow into the sea, including the Qiantang, Ou, and Minjiang. Most of the sea lies over the continental shelf, which extends out as much as 300 miles (480 kilometers) to the east. The East China Sea therefore is relatively shallow, seldom more than 656 feet (200 meters) deep. The Okinawa Trough, parallel to the Ryukyu Islands, is the deepest area, with depths to about 8,858 feet (2,700 meters).

Because the East China Sea is in a subtropical zone, the average annual temperature is 68–75 degrees F (20–24 degrees C); the annual temperature differential is 45–48 degrees F (7–9 degrees C). The average salinity of the East China Sea is 31–32 percent, and rises to 34 percent in the eastern areas. This is somewhat less salty than most global oceans, but not out of the ordinary for coastal seas.

One of the vital characteristics of this biome is the constant cycling of water in the East China Sea, which benefits by river inflow and by exchange with other oceanic regions. Colder waters enter the sea from the rivers and from upwelling along coasts. The Kuroshio Current, a major warming influence, moves north from near Taiwan. A flow known as the Taiwan Warm Current enters the Taiwan Strait from the Philippine Sea, through the Bashi Channel. Another flow, the Yellow Sea Warm Current, enters the northern part of the East China Sea to create an ideal habitat for fish and shellfish breeding, feeding, and winter survival.

Biodiversity

With its temperate climate; warm, shallow but well-stratified waters; seasonal flux in water exchange with other seas; freshwater supply from its rivers; and multiple areas of strong tidal action, the East China Sea offers a very robust, differentiated, and broad base for a multitude of plant communities and for many types of invertebrates, fish, marine mammals, and birds. It has been estimated that some 13,000 species exist here, of which nearly 48 percent are endemic, that is, found nowhere else on Earth.

The food web here benefits from the widespread propagation and growth of phytoplankton and zooplankton. In turn, these creatures form the basis of life for great populations of crustaceans and mollusks, which provide sustenance to all types of fish here.

As such, the East China Sea is the most productive marine area around China for seafood; it is especially rich in both big and small yellow fish, beltfish, flatfish, croaker, chub and spotted mackerel, Pacific cod, bluefin and bigeye tuna, a full range of sharks, squid, broadclub cuttlefish, and more. Most of the fishing is done by small local boats, but larger trawlers are a used in some cases. The Zhoushan Islands fishing grounds within the East China Sea are known as the treasure trove of China seafood production.

Spotted seal, finless porpoise, minke whale, and the critically endangered gray whale are among key marine mammals in these waters, roaming seasonally from the deeps to preferred grounds along the coasts.

The Yellow Sea-East China Sea region is an absolutely vital component of the East Asian-Australasian Flyway, with a reported two million shore birds stopping over on their northward migrations. Two globally threatened species are among these: spotted greenshank and spoon-billed sandpiper. Fulmars, storm petrels, alcids, geese, mallards, ducks, and other birds make up some of the 160 distinct marine bird species either resident in or that migrate through the East China Sea.

The short-tailed albatross, a vulnerable species that favors coastal upwelling zones for feeding areas, has important colonies in the East China Sea. The eastern curlew and Asian dowitcher are two additional vulnerable migrants here.

Environmental Threats

Environmental pollution caused by fast economic growth in mainland China as well as other nearby industrialized nations has led to conditions such as eutrophication (excess nutrients), low-oxygen zones, and frequent red tides along the coast of the East China Sea. Similarly, there have been repeated events of giant jellyfish swarms. Overfishing is a perennial challenge. Most of these conditions tend to be exacerbated by increasing water and air temperatures, with the onset of global warming. Sea-level rise, too, is a growing concern as it threatens coastal habitats with accelerated erosion and saltwater intrusion.

These factors have significantly affected the marine ecological web. In addition, air pollution from southeastern China is thought to form acid rain when passing above the East China Sea, thus precipitating heavy metal and toxic chemical fallout into the sea and along the north coast of Taiwan.

The East China Sea's continental shelf bears rich petroleum and natural gas deposits that have led to disputes among the bordering countries in the region, including China, Japan, South Korea, and Taiwan. The tension is focused on the control of the areas with potentially exploitable hydrocarbon reserves, particularly regions near deep trenches, straits, rocks, and uninhabited islands. Such disputes are incremental to already-existing conflicts over fishing rights in many of the same areas.

While diplomacy is required in struggle over fossil-fuel ownership, there are single-nation efforts to protect some of the East China Sea biome. Within the areas of the sea and coastal zones that it legally controls, the government of China has established seventeen nature reserves, seven special marine reserves, and a handful of fishery conservation areas. The total area of these marine protected areas (MPAs) is approximately 40,000 square miles (103,000 square kilometers). The intent of setting up and enforcing MPAs is to provide a future environment that preserves and restores biodiversity, habitats, and fishery resources.

Bibliography

Ding, H., et al. “An Overview of Spatial Management and Marine Protected Areas in the East China Sea.” Coastal Management 36, no. 5 (2008).

Hayes, Dennis E., ed. The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands. Washington, DC: American Geophysical Union, 1983.

Ishimatsu, Atsushi and Heung-Jae Lie, eds. Coastal Environmental and Ecosystem Issues of the East China Sea. Tokyo: Terrapub and Nagasaki University, 2010.

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

Qu, J., Z. Xu, Q. Long, L. Wang, X. Shen, J. Zhang, and Y. Cai. East China Sea—Global International Waters Assessment. Kalmar, Sweden: Linnaeus University and United Nations Environment Programme, 2005.

Teh, Louise, S.L. "Taking Stock: A Large Marine Ecosystem Perspective of Socio-Economic Ecological Trends in East China Sea Fisheries." Reviews in Fish Biology and Fisheries, vol. 30, pp. 269-92, doi.org/10.1007/s11160-020-09599-8. Accessed 1 Aug. 2022.

Zhu, Qian. Biological Assessment of the Ecologically Important Areas for Marine Mammals in the Yellow Sea Ecoregion. Weihai, China: Shandong University, 2008.