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31

B . M . Al - Chalabi 
Bull. Iraq nat. Hist. Mus. 
(2000) 9 (2): 31-36 
 

COMPARATIVE ECOLOY OF TWO SPECIES OF BIVALVE 
CORBICULA FL UMINEA AND CORBICULE FL UMINALIS IN 

SHATT AL-ARAB 
 

Y. T. Daoud 
Department of Biology. University of Babylon 

 
ABSTRACT 

Some aspects of population dynamics of both corbicula species inhabiting intertidal zone of 
shatt al-Arab are described. These informations are explained in accordance with the possible 
occurrence of competition between the two related species. 
 

INTRODUCTION 
The two Asian clams corbiculafluminalis (Muller. 1974) and corbiculaflurninalis (Muller. 
1974) are very common species in shatt al- Arab River. The two species are also recorded in 
Habbanya and Razzaza lake (Zahadin, 1965) and (Britton, 1977.( 
The genus corbicula plays an important role in transforming the energy and removing the 
suspended organic material from the water column to increase the natural precipitation of 
organic material (prokopovich. 1969.( 
It appears that the two species had similar ecological requirements. therefore they might be 
competition. However an explanation of their coexistence was given in this investigation 
through the study of dynamic of their populations. 
 

STUDY AREA 
Shall Al-Arab River is one of the main water bodies in Iraq. It is 139 km long from the point 
of the confluence of the Tigris and Euphrates Rivers to mouth north of the Arabian Gulf. The 
River is under tidal effect from the gulf and at low tide a wide strip of substratum on the two 
sides of the River become exposed. The chosen site for the study was part of this area and 
situated close to Basrah city. 
The intertidal area of shatt al-Arab in general. including the study site. is covered with water 
plants for most part of the year forming a green mat over its sandy mud substratum. The 
dominate plants are Phragniitis austvalis (Cay.): Tvpha doiningensis pers: Cvperus longus L:. 
Potarnogeton schweinfurthii L.; and Ceratophyllurn dernersum. Another abuadant plant is the 
Cladophora glornerata (L.). 
Chemico-physical condition of the Shatt al-Arab River had been reported by several workers. 
A water temperature varies between 10-32 C (Marina. in press). Water salanities showed 
seasonal and variations and differed between the parts of the River. The lower regions had 
salanities of typical of an estuary and much higher that those of the upper regions. Values 
recorded at the sampling site were between 0.5 and 1 .2%0 (Marian. in press). The hydrogen 
ion concentration ranged between 7-8 without vertical variations (Al-Saheb. 1989). Dissolved 
oxygen in the River was invariably near saturation which calcium was always much higher 

 



 

 

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Inheritance of dark head 
than minimum concentration required for gastropod survival (>100 mg-I) (Daud. at al. in 
press). 

 
MATERIAL AND METHODS 

Monthly sampling were collected from Nov. 1985 to October 1986. On each sampling 
occasion, fifteen quadrates (1/6 m-2) were taken from the intertidal area of the River. This 
position of a replicate was determined randomly’ a line transect running perpendicular to the 
water flow of the River. Individual replicates of each sample were carried in polyphone bags 
to the laboratory. They sorted by washing through a 0.4mm sieve. The number of clams per 
replicate was recorded and the length of each individual was recorded to nearest 0.1mm. 

 
RESULTS AND DISCUSSION 

This study concerns with the population dynamic and growth of C.flurninea and C/loin/na/is 
as revealed by changes in length of the shell. The shell of each species is thick and distinct. 
Growth rings usually assist in the assignment of individuals to age grouping. The shell 
dimensions of C.flurninea and C.flurninalis from shatt al-Arab are given in Fig 1. Which may 
assist in any subsequent study of population of the same or of different species. 
Monthly mean densities per replicate (0.0625% m-2) were calculated from 15 samples. The 
population of C.flurninea was at its maximum in December (21.66 per 1/16 m-I). Number 
then declined sharply until may. This could be due to the death of reproducing animals in 
early spring. After May mortality was relatively high and accounted for the reduction in 
number observed in July (2.2 per 1/16 m-l). In August again the density of population 
increased following by sharp in September. 
The density fluctuations C.flun2ina/is were or less follow the same general pattern of that of 
C.fluminea except that firstly, the mean density was significantly (P> 0.01) lower than that of 
C.fluniinea, secondly the two peaks of densities for C.flzirninalis were recorded with time leg 
of one and three month after the peaks of C.flurninea respectively. This might be attributed to 
avoid interference between the two Corbicula species. 
In recent years (1990-1992), unpublished data indicated that when the salanities were 
increased in shaft al-Arab (50%). the densities of C.flwninslis become significantly (P>0.01) 
more than the densities of C.flurninea. Kado & Murata(1974) reported that Cjlurninea is more 
adaptable to fresh water than Cf/urn/na/is. 
Analysis of population structure of both species of Carbicu/a in sail al-Arab as revealed by 
series of length frequency histograms suggest that at most of the year population comprised 
four age groups (0-year, 1-year. 2-years. 3-years) with average of shell length for C.flurninea 
and Cf/urn/na/is (2mm. 14.3mm. 20.3mm. 26mm) and (1.6mm. 15.8mm. 19mm. 21mm) 
respectively. 
The common feature revealed by the size class distribution of both Corbiczila species was the 
change in number of animal in each size class (Fig. 2). This change was attributed to growth. 
In November the dominant age groups C.fluminalis population were 1 and 2-year age group 
while for C. fluininea 2 and 3 year age group were dominant. In Junyary. and February. both 
species showed an increasing number of 0-year age group while the percentage of 3-year age 
group particularly for C.fluniinea was increasing in comparison with proceeding months. 
From April to June both species showed a considerable growth and may individuals of both 
species joined the 3-year age group. During the period from July-Agust, the population of 
both species underwent postreproductive moralities, it is clear that the number of individuals 
of 30- year age group was declined. 
To analyses the population structure from the competition point of view between the two 
related species, it could be noted that there is an obvious difference between the percentages 
of different age groups in certain months during the study period. Morton (1977) states that 



 

 

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B . M . Al - Chalabi 
each of Corbicula species may possess intrinsically different life cycles. Further more it was 
found that the growth rate of C.fluininalis was faster than that of C.fluminea. according very 
few individuals of C.Jlurninalis reached 3-year age group. Britton and Morton (1977) reported 
the same conclusion. Both populations also showed a continuous breeding which began in 
February and lasted until October. As sampling program for the percent study designed for 
one year. it would be difficult to given a complete picture about their life history. However 
Morton (1977) in plove core Reservoir in Hong Kong reported that life history of 
Cordiculafluininea lasted for about 3-years. 

 
REFERENCES 

Al-Saheb. L.M.A. 1989 Life history and production of tow species freshwater Bivalve 
Corbicula fluminea (Muller, 1974) and Corbiculaflurninalis (Muller. 
1974) in Shaft al-Arab Region. Unpublished M.Sc. thesis. Univ. of 
Basrah, Iraq. 

Britton. J.C. and Morton, B.S. 1977. Corbicula in North America: The evidence and reviewed 
and evaluated proceeding of the first International Corbicula symposium. 
Fort Worth 1977. Texas Christian Univ. Research Foundation, Fort worth. 
pp. 249-287. 

Daold, Y.T., Maring, B.A. and shihab. A.F. (in press) Life history and production of the 
gastropod Theoduxusjordani in the shatt al-Arab River. 

Kado, Y. and Murata, H. 1974 Reponses of brackish and fresh water clams Corbiculajaponica 
and C./eana, to variations in salanity.J. Sci. Hiroshima Univ.. SerB.. DivI. 
25: 217-224. 

 
Marina, B.A.Daold, Y.T. and shihab,A.F. (in press) Population Biology and production of 

Melanopsispraernorsa L. (Gastropoda) in the shatt al-Arab River. 
Morton, B.S. 1977 The population dynamics of Corbiculaflurninea (Bivalvia:Corbiculacea) in 

plover cove Reservoir Hong Kong. J.Zool. lond. 181: 21-42. 
Pokopovich, N.P.1969 Deposition of elastic sediments by clams. J. Sed. Petrology. 39: 891-

901. 
Zhadin, VI. 1965 Mollusks of fresh and brakish water of the U.SS.R. Academy of Sciences of 

the Union of Soviet Socialist Republics. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 



 

 

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Inheritance of dark head 
Bull. Iraq nat. Hist. Mus. 
(2000) 9 (2): 31-36