Biodiversity of China’s seas, coasts and islands

1 Species diversity of China’s seas

2 Ecosystem diversity of China’s seas

3 The diverse coastal ecosystem

4 Ecosystem diversity of China’s islands

5 Serious threats confronting the marine biodiversity of China’s seas

6 Efforts to protect the biodiversity of China’s seas, coasts and islands

1 Species diversity of China’s seas

The 20,278 species of organisms recorded from China’s seas belong to 5 kingdoms and 44 phyla. Of these, the Animalia includes 24 phyla, the most abundant species of which are the Arthropoda, Mollusca and Chordata with more than 2,500 species each. Of the six plant phyla, three are algae with 794 species and three are vascular plants with 413 species. Seven phyla of the Protista have nearly 5,000 species (Table 1).

Of the 24 animal phyla, 10 are exclusively marine. The number of species is more than in freshwaters but less than on land. Species numbers increase toward the south. China’s seas encompass both the southern boundary of many temperate species and the northern boundary of many tropical ones.

Table 1 The numbers of species recorded from China’s seas

Kingdom and phylun		Kingdom and phylum		Kingdom and phylum
MONERA	229	PLANTAE	1,203
Bacteria	79	Rhodophyta	443	Priapulida	2
Actinobacteria	18	Phaeophyta	153	Annelida	979
Cyanomyceta	131	Chlorophyta	194	Sipuncula	39
Prochlorophyta	1	Pteridophyta	11	Echiura	9
PROTISTA	4956	Gymnospermae	3	Mollusca	2554
Bacillariophyta	1395	Angiospermae	399	Arthropoda	29
Pyrrophyta	255	ANIMALIA	12794	Bryozoa	488
Chrysophyta	14	Porifera	106	Entoprocta	9
Xanthophyta	3	Coelenterata	989	Brachiopoda	8
Cryptophyta	1	Ctenophora	9	Phoronida	4
Ciliophora	291	Platyhelminthes	574	Chaetognatha	37
Sarcomastigophora	2997	Nemertea	52	Echinodermata	471
FUNGI	188	Kinorhyncha	10	Hemichordata	6
Yeast	61	Nematoda	122	Urochordata	125
Other fungi	127	Acanthocephala	32	vertebrata	3181
Mycophycophyta	1	Rotifera	17

2 Ecosystem diversity of China’s seas

Bordering mainland China are the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea with collective areas of 4.73 million km². The Yellow Sea and Bohai Sea are situated on the boundary of the north temperate region, and the East China Sea and South China Sea are in the subtropics. Each exhibits the characteristics of a large marine ecosystem. The Kuroshio Current, estuarine waters and up-welling areas in China’s neritic seas also show ecosystem level biodiversity.

(1) The Bohai Sea

The Bohai Sea is an inland sea on the mainland coast of China with an area of 80,000 km², a maximum depth of 70m and an average depth of 18m.

A total of 120 species of phytoplankton, dominated by eurythermal, low salinity, diatom species, have been recorded from the Bohai Sea. The dominant species are representative of the Coscinodiscacus, Chaetoceros, Rhizosolenia and Skeletonema costatum. There are also about 100 species of zooplankton, dominated by temperate low salinity and some oceanic species. The dominant species are Noctiluca scientillans, Calanus sinicus, Paracalanus parvus, Labidocera euchaeta, and Sagitta crasse. More than 100 species of benthic plants mainly warm temperate species with green algae dominant in the inter-tidal zone and brown and red algae dominant in subtidal zones, have been recorded. There are about 140 species of benthic animals which are also dominated by low salinity species. Of these, the species with a larger biomass and commercial fishing value are Scapharca subcrenata, Ruditapes philippinarum, Meretrix meretrix, Ostrea plicatula, Penaeus chinensis and Exopalaemon carinicauda. There are about 120 species of nekton, most of which are fishes, plus a few shrimps, crabs, squids and marine mammals. There are abort 20 main species of fish, such as Setipinna taty, Engraulis japonicus, Lateolabrax japonicus, Nibea albilora and Cynoglossus semilaevis.

(2) The Yellow Sea

The Yellow Sea is a semi-enclosed shallow continental sea with an area of 380,000 km², a mean depth of 44 m and a maximum depth of 140m. The circulation of the Yellow Sea is mainly influenced by the Yellow Sea Warm Current and coastal currents. Its continental shelf is mainly covered by pelitic and silty deposits. As it is located in the northern temperate zone, a unique biota which is characterized by an assemblage of elements from frigid, subfrigid, tropical and subtropical areas, in addition to native species.

A total of 386 species of phytoplankton have been recorded from the Yellow Sea which is dominated by representatives of the Coscinodiscacus, Biddulphia, Chaetoceros, Rhizosolenia, Nitzschia and Peridinium, with a variety of ecologies indicative of temperate seas.

A total of 130 species of zooplankton has been recorded. They are either warm temperate neritic species, typical of coastal currents, or warm water species from the Kuroshio. The dominant species are Calanus sinicus, Centropages memurrichi, Euphausia pacifica, Parathemisto gracilipes and Sagitta crassa.

Some 200 species of benthos have been recorded. Of these, the Polychaeta is the most numerous followed by the Mollusca, Crustacea and Echinodermata. There are also some widely distributed species such as Sternaspis scutata, Nereis longior, Eucymene annandalei, Ceratonereis erythraeenis, Tambalagmia fauveli, Leptochela gracilis, Amphioplus ancistrotus and Ophiura sarsii.

A total of 219 and 225 species of nekton have been recorded from the northern and the southern Yellow Sea, respectively. Fish are the most common species; together with shrimps, crabs, and squids. The most dominant species include Clupanodon punctatus, Setipinna taty, Harengula zundsi, Sardinella sp., Stromateoides argenteus, Ilisha elongatea, Cynoglossus semilaevis, Pseudodiaena polyactis, Nibea albiflora, Trichiurus haumela, Lateolabrax japonicus and Paralichthys olovaceus. There are, in addition, 15 species of whales, three pinnipedes and four turtles in the Yellow Sea.

(3) The East China Sea

The East China Sea has an area of 770 km² and a mean depth of 370 m over the continental shelf and a maximum depth of 2,719 m at the bottom of the continental slope. Coastal currents and the Taiwan Warm Current are important in the shallow waters of this sea.

A total of 64 species of phytoplankton occur in the waters near the estuary of the Yangtze River and 261 species occur off-shore in Zhejiang. The dominant algae are Skeletonema costatum, Coscinodiscacus spp., Chaetoceros lauderi and Nitzschia pungens. Neritic temperate species are the most common ecological type.

A total of 81 species of zooplankton occur close to the Yangtze River estuary and 223 species have been recorded from the coast of Zhejiang. Peaks in biomass occur in the summer. The main species are Calanus sinicus, Labidocera euchaeta, Pseudeuphausia sinica, Acartia pacifica and Sagitta enflata.

A total of 342 species of benthos have been recorded from the East China Sea. The Mollusca account for 77, the Polycheata 77, the Crustacea 95, the Echinodermata 136, the fishes 62, with 18 others.

There are 167 fishes recorded from the Yangtze River Estuary and shallow waters of the East China Sea. Of 203 species of nekton in the shallow waters of Zhejiang, common species of fish include Pseudosciaena crucea, Trichiarus haumela, Ilisha elongata, Stromateoides argenteus, Harpodon nekereus, Miichthys miiry, Muraenesox cinereus and Acetes chinensis. Other species include Exopalaemon carinicauda, Portunus trituberculatus, Charybdis japonica and Sepiella maindroni.

(4) The South China Sea

The South China Sea encompasses tropical and subtropical zones. It is a semi-enclosed sea with a continental margin and an area of 3.5 million km². There is a wide continental shelf, and 30% of the waters are deep with a mean depth of 1.4 km. Two main currents, a coastal current and the South China Sea Warm Current, occur in the northern South China Sea.

The number of phytoplankton species differs between regions and ranges from 104 to 260. They belong to two large groups, the diatoms and dinoflagellates, of which Chaetoceros and Rhizosolenia are dominant.

In the offshore waters of the northern and southern South China Sea, 130 and 250 species of zooplankton have been recorded, respectively, and of which the main ones are copepods. Zooplankton biomass forms a single peak over the course of each year.

Benthic organisms in the estuarine waters of the coast of Guangdong comprise 319 species most of which are tolerant of low salinities and occur in high numbers. In contrast, the benthos of the middle and western region of eastern Guangdong and the coastal waters of western Guangdong mostly comprise species with a high salinity tolerance, typical of the southern subtropics and tropics. A total of 820 species are dominated by the Mollusca, Arthropoda and Annelida. Most of the benthos along the coast of Hainan comprises tropical species, with a total of 755, dominated by corals, algae, molluscs and echinoderms. A total of 832 species recorded from along the coast of Guangxi are dominated by Turritella bacillum and Scapharca subcrenata. Of 135 species of benthos recorded from the Xisha Islands, 30.37% are crustaceans and the rest are mainly molluscs and echinoderms.

The nekton recorded from the northern South China Sea comprises 1,064 species, of which 100 are economically important, such as Decapterus maruadsi, Sardinella aurita, Pneumatophorus japonicus and Trachurus japonicus. It has been recorded that there are here some 200 species of shrimps belonging to Penaeus, Metapenaeopsis and Metapenaeus. Most of these are tropical and subtropical. The fishes comprise 535 species, and shrimps in the South China Sea are not characterized by dominant species. There are 58 species of cephalopod, of which 25 species, such as Todarodes pacificus, Nototodarus hawaiiensis and Sepiella sepia are of commercial value. Dominant species in the southern South China Sea are coral reef fishes and tropical oceanic fishes.

(5) The Kuroshio

The Kuroshio is the largest current passing along the continental shelf of China. As one of the strongest currents in the world, this hot water flow has a great influence on the shallow seas of China’s continental shelf. Based on the results of a survey of the current by Chinese scientists and a co-operative survey between China and Japan, 419 species of phytoplankton, 697 species of zooplankton, more than 180 larval and young fishes and 2,000 species of nekton have been identified from it.

Kuroshio organisms belong to different ecological groups. For example, the phytoplankton may include high thermohaline, low salinity and high thermophile, high salinity and low thermophile, and eurythermohaline species. Zooplankton may include warm temperate neritic and tropical oceanic species. Fishes may include pelagic, meso-pelagic and benthic species.

As is typical of high thermohaline waters, the Kuroshio can be detected by its indicator species, for example, phytoplankton such as Gossleriella tropica, Asterolampra marylandica, Cheatoceros dadayi, Ceratocorys bipes and Amphisolenia shauinslandi. More than twenty zooplankton species, such as Euchaeta concinna, E. marina, Pareuchatea russelli, Sagitta enflata, Liriope tetraphylla, Pseudoconchoecia concentrica, and Euphausia tenera, can also be used as indicators of the current.

(6) Estuaries

There are more than 1,500 rivers and streams draining into the seas along the coast of China. The huge input of freshwater and terrigenous material creates an unique estuarine ecosystem. In general, the species composition of an estuary is complicated and highly diversified. This can be demonstrated by reference to the species composition of three estuaries, i. e., the species of phytoplankton in the Pearl River, the Yangtze River, and the Yellow River estuaries are 64,103 and 224, respectively; the corresponding numbers of zooplankton are 105,66 and 133, benthos are 153,191 and 456, intertidal zone species are 41,195 and 189, and nekton are 189,144 and 356, again respectively.

The ecological types in these estuaries are different, e. g., the Pearl River Estuary is dominated by tropical and subtropical species with warm-water species as dominant nekton and the Yangtze River and Yellow River estuaries by cosmopolitan and temperate species with warm-temperate species as dominant nekton.

In spite of different ecological types, the uniqueness of the estuarine environment results in a similar community structure, i. e., they can all be divided into 3 categories: freshwater, brackish water, and marine water communities. For example, the composition of the fish fauna in the Yangtze River Estuary comprises: (1) 17.4% freshwater species mainly of the Cyprinidae and Cobitidae; (2) 21.6% brackish water species mainly of the Mugilidae and Gobiidae and (3) 57.2% marine water species mainly of the Clupeiformes, Beloniformes, Perciformes and Pleuronectiformes.

(7) Upwelling ecosystems

There are many up-welling areas in China’s seas, e. g., in the middle of the Bohai Sea the cold waters of the Yellow Sea, off-shore from the Shangdong Peninsula and Zhejiang the nearshore waters of southern Fujian, southwest of Taiwan, the nearshore waters of eastern Guangdong and along the southeast coast of Hainan. Some examples are as follows:

The offshore area in southern Fujian. Centered on the Nanpeng Archipelago, the upwelling area ranges from the Lishi Archipelago in Zhangpu, Fujian, to the Jiazj waters of Guangdong. In comparison to the open sea in summer, it is characterized by low temperature (2~4℃ lower than that of open sea), high salinity (some 0.5‰~1.5‰ higher), low dissolved oxygen levels (<4.4 ml/L) low oxygen saturation (<90%) and high nutrient levels (N⁺ 13.8 µmol/L, P⁺ 0.4 µmol/L). Pareuchaeta russelli, Euconchoecia maimai and Dolioletta gegenbauri are indicators of this upwelling water and appear in great numbers. The bacterial biomass may peak at 66.6 µg C/m³ and is dominated by coldwater luminescent species. In addition, phytoplankton density is high (>10⁸ cells/m³), with a high primary productivity [1.06g C/(m²·d)] and a total zooplankton biomass of more than 250 mg/m². Up-welling is a kind of wind-driven ascending current, i. e., a compensation current from the bottom water as a result of the southwestern land breeze occurring only in summer. Consequently, the fishing ground also only exists in summer.

The southern Taiwan Shoal. There exists, almost year round, a narrow band of low temperature, high salinity and high density water oriented in an east-west direction. The rapidly ascending isopleth trend in terms of temperature and salinity along the continental slope demonstrates the existence of a low pH centre and a surge of bottom water with high nutrient levels and low oxygen saturation. The indicator species, Calanoides carinatus, is found year round as is Callinitra emmae which comes from a depth of 5,000 m. High densities of eggs, larvae and young fishes, of which 9% are from the deep sea, enter this area. The upwelling climbs up with the bottom current along the slope, with the help of wind action in addition to the circulation pattern around the Taiwan Shoals. This upwelling is, thus, mainly topography-induced. Due to the permanent existence of upwelling in the area, a major fishing ground is present on the southern Taiwan Shoal year round.

Upwelling, as a special hydrological phenomenon, results in a special ecosystem. An upwelling ecosystem is generally characterized by its high productivity, a short food chain, a fast nutrient cycle and efficient energy transfer.

3 The diverse coastal ecosystem

(1) Intertidal ecosystems

According to an intertidal zone survey conducted during the period from 1981 to 1986, a total of 1,590 species, but probably several times that figure in practice, has been recorded from the shores of China. The number of species increases towards the south, i. e., it starts at 251 species in the Bohai Sea and reaches more than 971 in the South China Sea (Table 2). Except for those dominant eurythermal, euryhaline and cosmopolitan species, some are typical of temperate waters, such as Chthamalus challengeri, Stenothyra glabar and Styela clava, whereas others are typical tropical and subtropical species such as Euraphia witherisi, Nodilittorina trochoides and Styela plicata. The species on hard substrata of reefs and piles are different from species on soft bottoms of sand and mud.

Table 2 The numbers of intertidal species along the coast of China (1981-1986)

	Bohai Sea	Yellow Sea	East China Sea	South China Sea	Total
Cnidaria	6	12	9	22	38
Polychaeta	45	101	142	78	218
Mollusca	83	180	296	335	513
Crustacea	54	116	196	202	308
Echinodermata	8	22	30	54	78
Pisces	17	12	35	40	61
Algae	34	147	97	235	358
Others	4	15	6	5	16
Total	251	605	811	971	1590

The weight and diversity of the benthic biomass varies much between areas and sediment types, e. g., the wet weight of biomass in the Yellow Sea is as high as 2.199 g/m², compared with 217g/m² in the East China Sea. Density reaches 1,013 individuals/m² in the Bohai Sea but only 317 individuals/m² in the South China Sea. This also demonstrates that a discrepancy exists in terms of biomass on different substrata. The number of animals is much higher on a hard bottom than on a soft one. For example, the biomass of a coral reef is 41 times that of a mangrove mudflat. The same situation occurs with density. This is mostly due to the gregarious attachment of shells, such as barnacles and oysters, on hard substrata. The biomass of the intertidal zone is much higher than that of the shallow water benthos, demonstrating the high productivity of the intertidal zone.

Intertidal communities can be divided distinctly into 3 vertical zones: high, middle and low, related to the tidal exposure of the substratum. Species numbers and biomass are low in the high intertidal zone while they vary with location and substratum type in the middle and lower zones. This discrepancy between tidal zones cannot be generalized, or simply averaged. Biological zonation on a rocky shore is, however, clear. Usually, a littorinid-lichen-barnacle zone forms on the high intertidal. The dominant species of this zone are similar to those which occur in the Bohai and Yellow Seas. Here it is characterized by Chthamalus challengeri but this species does not occur in the East and South China Seas where the warm water species Nodilittorina, trochoides and Capitulum mitella take its place. Species inhabiting the middle tidal zone include the oyster Saccostrea sp., barnacles and green algae. Brown algae and red algae inhabit the low intertidal zone. In the Bohai Sea and Yellow Sea, Chthamalus challengeri is the exclusive dominant species of this zone. In contrast, species like Saccostrea echinata, S. mordax, Tetraclita squamosa squamosa, and species of Ulva and Gelidium, occur in great quanties in the East China Sea and South China Sea. Brown algae and red algae inhabit the low intertide zone. Sargassum pallidum is typical of the Yellow Sea. Warm water species, such as Sargassum henslowianum, Ishige okamurae, Hypnea japonica and Symphyocladia marchantioides can only be found to the south of the East China Sea.

(2) Coastal marsh-wetland ecosystem (Boreal)

There are many saline marshes and mudflats in estuaries to the north of Zhejiang. This kind of wetland, i. e., a biotope covered with grass vegetation high in the intertidal zone, mid tidal zone and supratidal zone, are mostly the habitat of birds and make up a marsh-wetland ecosystem. Such ecosystems can be found in the mudflats of the Yalujiang River Estuary, the Liaohe Delta, the Yellow River Delta, Laizhouwan Bay, Tianjin Beach in Bohai Bay, Dagu Estuary in Shandong, Yancheng Estuary in Jiangsu, Chongming Estuary of the Yangtze River, Nanhui district of Shanghai, the beaches of Hangzhou Bay and the beaches of the Yongjiang and Oujiang Rivers.

In marshes connecting freshwater and estuarine areas beyond the supra-tidal zone, wide areas of lush reeds (Phragmites communis) are distributed from the Yalujiang Estuary in the north to Hangzhou Bay in the south. Small patches of reed bed also occur in Guangdong. The area of reed bed in the Liaohe Delta is 67,000 ha. Seaward of the reed bed in the high intertidal zone, vast areas of short vegetation such as Salsola glauca and Salicornia europaea are found. In the high intertidal zone of the Yangtze River Estuary and Hangzhou Bay, Scirpus marigueter grows in large areas of marsh. For example, its community of Jin Si Niang Bridge, Pin Hu, on the northern coast of Hangzhou Bay has an area of 500×3,000 m², a height of 20 cm and 85% cover.

Up to 1992, the grasses Spartina anglica and S. alterniflora introduced from England in 1963 and from America in 1979, respectively, have grown and spread to cover 6,000 ha of the high intertidal zone along stretches of the coast from Liaoning to Guangxi. They form an artificial biotope, especially in Jiangsu and Zhejiang.

Table 3 lists 8 representative wetland grass communities with their relevant migrants from the Yalujiang Estuary to Hangzhou Bay.

Table 3 Some representative wetland grass communities and birds

along the coastal regions of northern and middle China

Mud flat	Vegetation		Birds recorded and species numbers
	Reed bed	Others
Yalujian River Estuary	11,000 ha	Salsola glauca, Salicornia europaea	>70 species, Cygnus cygnus, Egretta eulophots
Liaohe Delta	67,000 ha	S. glauca, S. europaea