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Chapter 57. Distribution of modern ostracods in the shelf seas off China

Chapter 57. Distribution of modern ostracods in the shelf seas off China

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806 Q.-H. ZHAOAND P.-x.WANO



TEXT-FIG.

l-Bathymetry. sampling stations and sediment types in the shelf seas off China (for graphical reasons

some of the stations are omitted).



ABUNDANCE

AND DIVERSITY

Rich ostracod faunas were found in all the shelf seas under consideration. A total of 116 species

belonging to 68 genera were identified in the Bohai Gulf and the Yellow Sea, 126 species representing 83 genera in the East China Sea and 190 species from 90 genera in the northern part of the

South China Sea.

The distribution of ostracod abundance (number of valves per gram of sediment) and diversity

(number of species per sample) is shown in Text-figs. 2,3 and Table 1. It can be seen that both the

abundance and diversity increase generally from the north to the south, from the coast to the shelf

edge. The lowest values (<10 species per sample, < 1 valve per gram) occur in the estuarine and

coastal zones with water depths of less than 20m and in the central part of the Huanghai Sea with



807

105"

.



110"



115"



120"



125"



130



0< 1



10"



1-10



rn 10-20



=

--,-)



20-30



>30

85



200m isobath



10"



r'



'5



/I



-Y



/' '



0"



TEXT-FIG.

2-Distribution of ostracod abundance in the surface sediments of the shelf seas off China (number of

valves per gram of dry sediment).



105"



r



110"



115"

r



120"



125"



130"

t.



40"



,--,200m isobath

35"



30'



25"



20



TEXT-FIG.3- -Distribution of number of species of ostracods in the surface sediments of the shelf seas off China.



808 Q.-H. ZHAOAND P.-X. WANO



TABLEA AVERAGE OSTRACOD

ABUNDANCE

AND DIVERSITY

IN SURFACES

SEDIMENTS

OF THE SHELF

SEASOFF CHINA

Water Depth Range



20m



Sea Area

Huanghai Sea and Bohai Gulf

East China Sea

North Part of South China Sea

Sea Area

Huanghai Sea and Bohai Gulf

East China Sea

North Part of South China Sea



10.4

2.2

18.6



20-50m



50-1 OOm



100-1 50m



average number of valves per gram of sediment

9.3

2.8

4.6

11.5



17.7

33.3



17.2

27.7



average number of species per sample

11.4

7.6

10.6

21.4

18.1

22.1

36.7

31.5



14.7

7.7

15.8



150-2OOm



4.6

22.0



11.8

29.2



water depths of over 50 m. The low concentration and diversity of ostracods can be attributed to

high sedimentation rate and to low water temperature and salinity, since the central part of the

Huanghai Sea is occupied by the Huanghai Cold Water Mass and the estuarine and coastal zones

are dominated by diluted water of variable temperature. The middle and outer shelves of the East



x



I



--___iouthern limit



n

northern limit



TEXT-FIG.

4-Occurrence of some cold-water and warm-water species in the shelf seas off China:

Cold-water species: 1, Howeina camptocytheroidea; 2, Acanthocythereismutsuensis; 3 , Sarsicytheridea bradii; 4, Finmarchinella huanghaiensis; 5, Cytheromorpha acupunctata; 6, Loxoconcha hattorii; 7, Cytherop

teron sawanensis.

Warm-water species : 8, Cytherelloidea senkakuensis; 9, Paoenborchella iocosa P. malaiensis; 10, Cytherelloidea yingliensis; 1 1, Uroleberis faveolata; 12, Neonesidea haikangensis.



+



species

R a d i m e l l a spp.

Lcococcncfia turmlosun

L.

lilljeborchi

Atjehella ki@

Cytherelloidsa 1-i

Qthercptemn sinensis

Laxoconha ptercgma

M k r i t h e orientalis

Cytherella p3sterotuberCula

Neoqtheretta s n e l l i i

Bradleya albatmssia

Qtherelloidea yingliensis

P a i j e h r d e l l a i-a

+ P. malaiensis

Qthetoqtheretta apta

B i c D m u q t h e r e euplectella

Nemesi&a haikanqsmis

U r o l e k e r i s fowolata

.NamcYpris &Cora

Xestoleberis variegata

Spinocythere fragosa

Lommnha sinensis

Abrorythereis q u a n q d o ~ n s i s

Argil&&a hanaii

Trxhylekeris scabrccuneata

Acanthoqthereis ? n i i t s d

AlooJpocythere profusa

A u r i l a qnba

Cushmanidea s b j j n i c a

Cythemptemn miurense

Mmseyella japmica

Stigmtocythere spincsa

Xestaleberis hanaii

Bicomucytkre bisanensis

Widmamella bradyi + W. b r a d y f o d s

B y t h w e r a t i ~cassidoidea

Mcnooeratina alispinata

Hirsutocythere ? hanaii

k k q t h e r e retiaiiata

Anphileberis g i b k r a

Niprpnocrthere &a

&pytu.i pastercsulcls

Mum-ratina

crispata

Sinocytheridsa latiovata + S. longa

Sinocythere spp.

Buntmia hanaii

Cytherelloidea senkakuersis

Actimrythereis kisarazuxsis

s43nicythenrra ~nandniFpJnica

Cytheropteron uchioi

C.

SIblldliOi

Acanthxythereis nunechikai

Bradleya j aponica

Albileberis spp.

Leptocythere wntriclivosa

--&a

ocellata

Munseyella p q i l l a

KabayaShiiM m a i e m i s

Krithe swaensis

Propcntccypris euryhalina

Spinileberis furuyaersis + S. pulcfira

Tanella opima

Cytheroptenn sawaremis

Lcmccncfia hattorii

FinaKfiinella huarqhaiensis

Acanthcqthereis rmtsuensis

Sarsicytheridea bradii

Haeina canptcqtheroidea



TEXT-FIG.

5-Latitudinal

(=

abundunt;



,



distribution of common species of Ostracoda in the shelf seas off China.



0few).



810 Q.-H. ZHAOAND P.-X. WANO



China Sea and the northern part of the South China Sea, on the contrary, are controlled by the

Kuroshio Current and hence are distinguished by high temperature and salinity, apart from the low

sedimentation rate of terrigenous material. As a result, the ostracod concentration and diversity are

high in these areas, with more than 10 valves per gram and more than 20 species per sample.



DISTRIBUTION

OF SPECIES

As revealed by distribution patterns of individual species in the sea areas studied (see Wang and

Zhao, 1985; Wang, Min and Gao, 1980; Wang et al., in press; Zhao, Wang and Zhang, 1985),

temperature, salinity and water depth are major environmental factors controlling the areal distribution of Ostracoda.

The China Sea extends across three climatic zones : tropical, subtropical and temperate zone.

However, the bottom-water isotherms are not parallel to the latitudes and their pattern is complicated by the influence of the water masses and currents. For example, warm-water species typical

of the South China Sea - Bicornucythere euplectella (Brady), Cytherelloidea yingliensis Guan,

Neonesidea haikangensis (Guan), Uroleberisfoveolata (Brady), Neocytheretta snellii (Kingma), Loxoconcha sinensis Brady, Xestoleberis variegata Brady, Paijenborchella malaensis Kingma, P. iocosa

Kingma etc., also occur in the outer shelf area of the East China Sea and are believed to be brought

northwards by the warm water of the Kuroshio Current (Text-fig. 4). On the other hand, cold-water

species like Finmarchinella huanghaiensisZhao, Cytheropteron sawanensis Hanai, Loxoconcha hattorii Ishizaki, Cytheropteron acupunctata (Brady) and Howeina camptocytheridea Hanai are mainly

bound to the Huanghai Cold Water Mass, but are distributed by the coastal currents in the northwestern part of the East China Sea as well (Text-fig. 4). The latitudinal occurrence of common species is summarised in Text-fig. 5 . In respect to temperature adaptation, three types of species may



!

digohaline



I



species



mesohaline



polyhaline



euhaline



Pnpontocypris euryhalina



Sinaytheridea Iatiovata

Tanella opim

Spinilekeris pulchra

Albileberis sinensis

A.

sheyangensis

Leptocythxe ventriclivosa

Lmomncha ocellata

Sinoqtheridea lmga

Spinileberis furuyaensis

comonOcyulere sinensis

Spinileberis quackiaculeata

Pontoqthere littoralis

Neomxloceratina crispata

Widmann4la bradyfonuis

Sinocythere sinensis

S.

? reticulata

Biwmucythcxe bisarensis

Aurila q n b a

Xestoleberis hanaii



=



SEE



TEXT-FIG.

&Salinity ranges of common species of Ostracoda in the coastal areas of the China Sea.

abundant;



0common; - few; --- rare.



species



shelf

0



Prcpmtocypris euryhalina

SpMleberis funyaensis + S. pulchra

T a d l a opima

Laccon& ocellata

kptocythere m t r i c l i v n s a

albileberis spp.

Sinocytheridea latiovata + S. lmga

Radimlla spp.

tmoam&a twrulcsun

6.

lilljeborchi

partocythere l i t t o r a l i s

Lamconcha h a t t o r i i

bhmnicka spp.

Sinocythere spp.

?=nella

huanghaiersis

yulexptercm sawammiis

Wtmnoczratina crispata

CLcomUcythere bisanensis

hmseyella j@Ca

+ M. pupilla

?iicfimwnellabradyi + W. b r a d y f o d s

Llocopocythere profusa

itigmtoqthere spincsa

rurila CyntM

kstoleberis hanaii

ytherq3teron InilKerEe



rathocythereis ? niitsuwi



lowxlxlcha sinersis

W

u

L

3



postemulcui



iemlkmthe orientalis



-&a



P t e v



'racfryleteris scabrocuneata



Cathocythereis rrmtsuensis

irsutocythere ? hanaii

obqmhiina dmgtaiersis

n@ileberis gikkera

"df"y" j e arsicythetldea bradii

&ria asnnptocytheroidea

ytheroptem subuchioi

lmccythere o b s a

athetocythretta apta

qilloecia hanaii

haythere M c u l a t a

icomucythere ewlectella

-idea

haikangersis

&hxcp&rcnuchioi

mleberis fovmlata

rthercpteron sinxsis

m t d a hanaii

anthocythereis mnechikai

rtherelloidea spp.

kinoqthereis kisarazwnsis

mxythereis guanqb~gemis

rthoaeratina cassidoidea

Athe Sawamnsis

dnoqthere fragc6a

stoleberis variegata

oqtheretta snellii

micytterura minaminipponica

mcceratina alispinata

adleya a l b a t m s i a

IcTocyPTiS decors



TEXT-FIG.

7-Depth ranges of common ostracod species in the shelf seas off China.



(mabundant; 0few).



200



IIJII



812 Q.-H. ZHAOAND P.-X. WANO



be distinguished in the shelf seas off China: 1. warm-water species inhabiting the South China Sea

and/or the East China Sea, with a few occurrences in the southern part of the Huanghai Sea; 2.

coldwater species distributed mainly in the Huanghai Sea and the Bohai Gulf; 3. eurythermal

species found in coastal waters all along the shoreline of the Chinese mainland.

As for the water salinity, there is a general tendency for it to increase southwards and seawards

in the sea areas studied. In the open seas, where the salinity variation is negligible, all ostracod species

are stenohaline in nature and the water temperature is the main factor controlling their distribution,

whereas in coastal and estuarine areas with significant salinity variations in space and time, the

ostracod fauna is dominated by euryhaline and hypohaline forms. According to our ecological

survey of living ostracods along the Chinese coast (Zhao, 1984, 1985), the salinity ranges of common eury and hypo-haline species are shown in Text-fig. 6. Worth noting are some euryhaline

genera such as Sinocytheridea and Albileberis which are dominant and widespread in the Chinese

coastal waters, but have as yet never been reported elsewhere. The world-wide brackish-water form

Cyprideis torosa (Jones) is conspicuously absent along the Chinese coast and is probably replaced

by the endemic species Sinocytheridea latiovata Hou et Chen.

Depth ranges of common ostracod species in the shelf seas off China are given in Text-fig. 7.

According to depth occurrence it is possible to distinguish supralittoral, littoral, inner shelf and

other forms. However, it has been shown that the water depth in itself is not a purely independent

factor in determining the faunal distribution, because many environmental factors such as hydrostatic pressure, density, temperature, salinity, pH, oxygen, diaphaneity, nutrients, etc., change with

it. If the same environmental conditions occur at different depths in different areas, the depth range

of ostracod species may also be changed. Examples are the warm-water species Neonesidea haikangensis, Uroleberis foveolata and Loxoconcha sinensis which spread all over the shelf in the South

China Sea ranging from the inner to outer part, but are limited to the outer shelf in the East China

Sea where the Kuroshio current is running through. The difference in their depth occurrences can

obviously be ascribed to the temperature.



DISTRIBUTION

OF ASSEMBLAGES

In our previous works, several ostracod assemblages have been dstinguished for each sea off

China: three assemblages for the Bohai Gulf (Wang and Bian, 1985), five for the Huanghai Sea

(Wang, Min and Gao, 1980), nine for the East China Sea (Wang and Zhao, 1985), and five for the

South China Sea (Zhao, Wang and Zhang, 1985). When all these data from individual seas are compared with each other and are summarised, five major ostracod assemblages may be recognised for

the entire shelf of the China Sea (Text-fig. 8).

Assemblage I (Pl. 1, Figs. 1-9) is dominated by Sinocytheridea fatiovata, S . fonga Hou et Chen,

and Neomonoceratina crispata Hu and is widely distributed in coastal and estuarine areas less than

20 m deep all along the Chinese coastline. Some species (e.g.,Albileberis sinensis Hou, Leptocythere

ventriclivosa Chen and Loxoconcha ocellata Ho) are common in all the areas studied except the

South China Sea where they are absent presumably due to its relatively high temperature. Moreover, the species composition also varies with the difference in salinity. Thus, Tanella opima Chen,

Propontocypris euryhalina Zhao, Spinileberis furuyaensis Ishizaki and Kato and S. pulchra Chen

are more frequent in oligo-and mesohaline waters, while in poly and euhaline waters some elements

from Assemblage I1 ( Wichmannella bradyformis, Bicornucythere bisanensis, Sinocythere sinensis

and S.? reticulata among others) are common. In fact, this is an eurythermal and euryhaline assemblage.

Assemblage I1 (Pl. 1, Figs. 10-25) is composed of eurythermal, but stenohaline, shallow-water



Modern Osrracoda in Sherf Seas offChina 813



TEXT-FIG.

8-Distribution of five major ostracod assemblages in the shelf seas off China.



species and occurs on the inner shelf at water depths of about 20-50 m throughout all the seas under

consideration. Wichmannella bradyformis (Ishizaki), Bicornucythere bisanensis (Okubo), Mwtseyella pupilla Chen, M . japonica (Hanai), Cytheropteron miurense Hanai are dominant and Aurila

cymba (Brady), Cushmanidea spp., Wichmannella bradyi (Ishizaki), Stigmatocythere spinosa (Hu),

Sinocythere sinensis Hou, S . ? reticulata Chen, Nipponocythere bicarinata (Brady), Neomonoceratina crispata and Sinocytheridea latiovata are common. Again, there are variations in species composition related to water temperature. For example, there are warm-water forms like Loxoconcha

sinensis, Hemikrithe orientalis Bold and Copytus posterosulcus Wang in the South China Sea,

and cold-water forms like Finmarchinella huanghaiensis, Cytheropteron sawanensis and Loxoconcha

hattorii in the Huanghai Sea. Generally, this is an eurythermal but stenohaline assemblage.

Assembage I11(PI. 1,Figs. 26-32; P1.2, Figs. 1-3) is distinguished by the cold-water character of

its dominant and common species with a relatively low species diversity. The assemblage occurs in

the central and deeper part of the Huanghai Sea (beyond the 50 m isobath) occupied by the Huanghai Cold Water Mass and, hence, can be called the Cold Water Mass Assemblage. Two subassemblages may be distinguished: the Northern Subassemblage is characterised and dominated by the

typical cold-water species Howeina camptocytheroides, Sarsicytheridea bradii (Norman) and and

Acanthocythereis mutsuensis Ishizaki, with F. huanghaiensis, C. sawanensis and others as common

forms; while in the Southern Subassemblage more eurythermal, cold-water species like Amphileberis gibbera Guan, Buntonia hanaii Yajima, Kobayashiina donghaiensis Zhao and Krithe sawanensis Hanai are dominant and Ambocythere reticulata Jiang and Wu, Nipponocythere obesa (Hu),

Cluthia ishizaki Zhao and others are common. The boundary between the two subassemblagesis

at approximately latitude 36"N.

Assemblage IV (Pl. 2, Figs. 4-25) is distributed beyond the 40-50 m isobath in the middle and

outer shelves of the East China Sea and the northern part of the South China Sea, being closely

related to the open-sea water and the Kuroshio Current with its branches. The assemblage is

characterised by a great number of warm-water species and a high diversity and abundance; hence



814



Modern Ostracoda in Shelf' Seas off China 815



it may be termed a warm-water assemblage. The dominant and characteristic species include Argilloecia hanaii Ishizaki, Cathetocytheretta apta Guan, Cytherelloidea senkakuensis Nohara, C .

yingliensis, Loxoconcha sinensis, Neocytheretta snellii (Kingma), Neonesidea haikangensis, Uroleberis foveolata and Xestoleberis variegata among others. The assemblage may be further subdivided

into at least two subassemblages: the East China Sea Subassemblage with more frequent Bradleya

japonica Benson, Hirsutocythere? hanaii, Cytheropteron uchioi Hanai, C . subuchioi Zhao and Semicytherura minaminipponica Ishizaki, and the South China Sea assemblage with Cytherelloidea

leroyi Keij, Bradleya albatrossia Benson, Cytherella posterotuberculata Kingma, Cytheropteron

sinensis Zhao and Loxoconcha pterogona Zhao.

Assemblage V (PI. 2, Figs. 26-32) is found in the coral reef area in the southern part of

Hainan Island and the Xisha Islands. All the major elements such as Radimella virgata Hu, R.

macroloba Hu, R . parviloba Hu, Loxoconcha tumulosa (Hu), L . lilljeborchi Brady, Treibelina rectangulata Hu, Paranesidea s p . and Keijia novilunaris Zhao are tropical in nature. Therefore, this

is a tropical coral-reef assemblage.

To sum up, the distribution of ostracod assemblages in the area is principally determined by the

water temperature and salinity, which in turn are controlled by the distribution pattern of water

masses and currents, apart from the latitude. Both Assemblage I and Assemblage 11 are basically

consistent in species composition from north to south, implying the similarity of coastal waters

along the entire shoreline of the Chinese mainland. The two assemblages differ from each other in

their salinity adaptation. All the other three assemblages are related to temperature conditions:

Assemblage 111 represents the Huanghai Cold Water Mass, Assemblage IV corresponds to the

warm-water Kuroshio system, and Assemblage V to the tropical surface water in the southern part

of the South China Sea.



ZOOGEOGRAPHY

Despite the numerous contributions to ostracod studies in East Asia, a systematic zoogeographical study is still wanting. In a discussion on ostracod zoogeography of the Pacific, Benson (1964)

divided the western coast of the Pacific into two realms: the Japonic Realm and the Indo-West

Pacific Realm, with a boundary running through the south of the East China Sea. This is, probably,

the only ostracod biogeographical zonation of East Asia now available in the literature. Since

then, a considerable amount of information has been accumulated on ostracod taxonomy and areal

PLATEI-Assemblage I : Fig. 1. Sinocytheridea latiovata Hou et Chen. Left valve, ~ 4 5 Fig.

.

2. Sinocytheridea

longa Hou et Chen. Right valve, ~ 4 5 .Fig. 3. Neomonoceratina crispafa Hu. Left valve, x 50. Fig. 4.

Albileberis sinensis Hou. Right valve, x 55. Fig. 5. Leptocythere ventriclivosa Chen. Right valve, x 55. Fig. 6 .

Loxoconcha ocellata Ho. Left valve, x 50. Fig. 7. Tanella opima Chen. Right valve, x 55. Fig. 8. Propontocypris

euryhalina Zhao. Left view of carapace, x 55. Fig. 9. Spinileberis ficruyazsis lshizaki et Kato. Left valve, X 50.

Assemblage 11: Fig. 10. Bicornucythere bisanensis (Okubo). Right valve, X 40. Fig. 11. Wichmannella bradyformis

(Ishizaki). Right valve, ~ 4 5 Fig.

.

12. Wichmannellu bradyi (Ishizaki). Left valve, ~ 4 0 Fig.

.

13. Munseyella japonica (Hanai). Right valve, x 80. Fig. 14. Munseyella pupilla Chen. Right valve, x 80. Fig. 15. Cytheropteron

miurense Hanai. Right valve, ~ 6 0 Fig.

.

16. Aurila cymba (Brady). Right valve, x 50. Fig. 17. Stigmatocythere

spinosa (Hu). Left valve, x 60. Fig. 18. Sinocythere sinensis Hou. Left valve, x 60. Fig. 19. Nipponocythere bicarinata (Brady). Left valve, x 65. Fig. 20. Alocopocythere profusa Guan. Right valve, ~ 4 0 Fig.

. 21. Acanthocythereis niitsumai (Ishizaki). Right valve, x 45. Fig. 22. Loxoconcha hattorii lshizaki. Right valve, X 55. Fig.

23-Cytheromorpha acupunctata (Brady). Left valve, x 6 0 ; Fig. 24-Copytus posterosulcus P. Wang. Left valve,

x 55. Fig. 25. Hemikrithe orientalis Bold. Left valve, X 55.

Assemblage I I I : Fig. 26. Howeina camptocytheroidea Hanai. Right valve, X 50. Fig. 27. Sarsicytheridea bradii

(Norman). Right valve, x 35. Fig. 28. Acanthocythereis mutsuensis lshizaki. Left valve, X 30. Fig. 29. Finmarchinella huanghaiensis Zhao. Left valve, x 60. Fig. 30. Cytheropterorz sawanensis Hanai. Right valve, X 80. Fig.

31. Amphileberis gibbera Guan. Right valve, X 50. Fig. 32. Buntonia hanaii Yajima. Right valve, X55.



816



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