conclusion

MORPHOLOGICAL COMPARISON BETWEEN GEOGRAPHICALLY DISTANT POPULATIONS OF THE PEARL OYSTER MORPHOLOGICAL COMPARISON BETWEEN GEOGRAPHICALLY DISTANT POPULATIONS OF THE PEARL OYSTER PINCTADA RADIATAPINCTADA RADIATA INVADING THE INVADING THE EASTERN MEDITERRANEAN SEAEASTERN MEDITERRANEAN SEA

CONCLUSION

There is no differences observed according to an east-west transect. Pinctada radiata is adapting to its new environmental conditions in spite of the geographic distance from its native area. Saronikos Gulf (Greece) population have the greater values and animals from Kerkennah Islands (Tunisia) present significant differences from all the other sites and have the lowest values in all parameters measured. It is assumed that environmental parameters are responsible for the observed morphometrical differences and shell morphology of Pinctada radiata has been shown to vary especially with salinity (Al Sayed & al., 1997). In Tunisia, the thermic conditions are very favorable and enable high fecundities of Pinctada radiata (Zouari and Zaouali,1994 ), just like for the other bivalves. This situation leads to different modalities of growth.

Aloui-Bejaoui, N.Aloui-Bejaoui, N. (1), E. Soufi (1), Zenetos A (2), A. Dosi (2), I. Ammar (3), and A. Ibrahim (3), (1), E. Soufi (1), Zenetos A (2), A. Dosi (2), I. Ammar (3), and A. Ibrahim (3),

(1)(1) Institut National Agronomique de Tunisie- 43, Avenue Charles Nicolle, 1082 Tunis, TUNISIA Institut National Agronomique de Tunisie- 43, Avenue Charles Nicolle, 1082 Tunis, TUNISIA (2)(2) Hellenic Centre for Marine Research, Institute Oceanography, P.O. Box 712, Anavissos 19013, GREECE, Hellenic Centre for Marine Research, Institute Oceanography, P.O. Box 712, Anavissos 19013, GREECE,

(3)(3) High Institute of Marine Research, Tishreen University, P.O. Box 2242, Lattakia, SYRIAHigh Institute of Marine Research, Tishreen University, P.O. Box 2242, Lattakia, SYRIA

9th International Conference on Shellfish RestorationNovember 15–19, 2006 - Charleston, South Carolina, USA

RESULTSINTRODUCTION

Pinctada radiata is a bivalve mollusc originating from the Indo-Pacific and the Red Sea (Oliverio and al., 1992). Following the opening of the Suez Canal, P. radiata has entered the far eastern Mediterranean. In addition, the species, being of commercial value (pearl oyster), has been imported for mariculture in other areas such as Greece and Italy. Up to date it has been recorded as common in the eastern Mediterranean with sporadic occurrences in the western basin (Zenetos & al., 2003).

The species’ mode of introduction in the areas beyond those of the Levantine basin, where Pinctada has progressively penetrated (Lessepsian migration), remains unknown. For example, the recent records in Greek waters correspond to areas where the species was intentionally introduced for marine farming (Serbetis, 1963). In addition, its presence in areas with major harbours indicates that shipping may be a alternative mode of introduction (www.ciesm.org/atlas/).

This study is a first approach towards investigation of the mode of introduction in the Mediterranean populations along an east-west transect. The aim of the study is to know :

•Are there differences between the populations in the different areas in these countries?

•Are there population differences between the three countries?

For this study 100 specimens per population were collected and examined morphologically using standard biometric techniques. Measurements were carried out using precise instruments : electronic digital calliper at 0.01mm precision and electronic scale at 0.01g precision. Five morphological parameters were considered with the object to compare the five sites :

- Height H

- Width W

- Thickness T

- Total weight (except for site SA1)

- Dorsal side (DS)

The analysis concerns:

1- Comparison of morphological parameters with the use of statistical tests (Kruskal-Wallis test ).

2- Comparison of C and R coefficients according to Hynd (1955)

3- Study of the relative growth parameters (Dagnélie, 1982; Box and Cox,1982) in each population using allometric tests (regression lines)

4- Analysis of morphological parameters’ variation based on the

use of a standard animal (Aloui-Bejaoui &. al., 2003).

W

H

DS

T

Bubble Chart for DS

Thickness (mm)

Hei

ght

(mm

)

StationSA1 KER LAT ROD SA2

0 10 20 30 400

20

40

60

80

100Bubble Chart for DS

Thickness (mm)

Hei

ght

(mm

)


0 10 20 30 400

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40

60

80


Thickness (mm)

Wid

th(m

m)


0 10 20 30 400

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Thickness (mm)

Wid

th(m

m)


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References

The Kruskal-Wallis test tests the null hypothesis that the medians of one parameter within each of the 5 levels of Station are the same. The data from all the levels is first combined and ranked from smallest to largest. The average rank is then computed for the data at each level. Since the P-value is less than 0,05, there is a statistically significant difference amongst the medians at the 95,0% confidence level. The Box-and-Whisker Plot determine which medians are significantly different from which others.

Rho

Lat

Ker

C= convexity = thickness / Height

0,3030,3670,3500,295

0,366

0

0,1

0,2

0,3

0,4

0,5

LAT KER SA2 SA1 ROD

R = Height / DS

1,3131,267 1,167 1,286 1,463

0

0,5

1

1,5

2

LAT KER SA2 SA1 ROD

Total weight (g) standard animal 50 mm Height

17,545

14,132

20,16620,218

0

5

10

15

20

25

SA2 LAT KER ROD

MATERIAL AND STUDY AREAS

Individuals were collected from 5 different sites. Three prominent established populations of Pinctada radiata have been selected from Greece: the populations of Rodos (ROD) and Saronikos Bay (SA1, SA2), one population from Tunisia Kerkennah islands (KER) and one from Syria, Lattakia area (LAT). Sampling was carried out by diving.

Comparison of morphological parameters with the use of statistical tests and Box and Whisker Plot :

Box-and-Whisker Plot

Station

Hei

ght

(mm

)

SA1 KER LAT ROD SA20

20

40

60

80

100


Station

Hei

ght

(mm

)


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Wid

th(m

m)


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m)


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Station

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ckne

ss(m

m)


10

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40


Station

Thi

ckne

ss(m

m)


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40


Station

Tot

alW

et W

t(g

)

KER LAT ROD SA20

10

20

30

40

50

60Box-and-Whisker Plot

Station

Tot

alW

et W

t(g

)

KER LAT ROD SA20

10

20

30

40

50

60


Station

Dor

sal

Side

(mm

)


20

40

60

80


Station

Dor

sal

Side

(mm

)


20

40

60

80

The equations of the regression lines have permitted to calculate the theoric values of weight after having fixed the value of the metric parameters of the individuals belonging to the different populations (standard animal). This value has been fixed in a way it could be the nearest possible of the means calculated refering to the different populations : H=50 mm

The more important total weight of a 50 mm height standard animal is observed in SA2 and LAT and the lowest one in KER. All the results confirm a better relative growth of the populations of Saronikos Gulf (height and width). The total weight in SA2 is more important than in the other populations. The population of KER presents the lowest values. The population of LAT presents a good development in total weight, comparatively to its metric growth. Among the three populations of Greece, ROD is the one that presents the less good growth in terms of height and total weight. This population shows a shape which develops more in width.

To summarize the results and visualize better the differences between sites we performed a Euclidean clustering method for all measured parameters except Total Wet Weight. The produced dendrogram suggests that the SA1 population is completely different from all the others which form two subgroups, the Greek sites together (SA2 and ROD) and the Syrian and Tunisian (LAT and KER) on the other subgroup.

These differences are also obvious on the following graphs:

The Kruskal-Wallis Test of the Medians results in significant difference amongst the populations for the Height (Test statistic=162,78, P-value <0,001), the width (Test statistic=164,14, P-value <0,001 ), the thickness (Test statistic=203,98, P-value <0,001), the dorsal side (Test statistic=132,77, P-value <0,001) and the total weight (Test statistic=138,35, P-value <0,001) at the 95% confidence interval .

The Student T-test as well as the Box and Whisker Plot indicates that animals from Saronikos Gulf (SA1) present the:

- higher values for height followed by the ROD , SA2 and LAT populations. KER present the lowest values.

- greater values for width, as it was observed for height, and animals from Tunisia (KER) the lowest.

- higher values for thickness followed by the LAT, ROD and SA2 populations which seem not to differ significantly and at the end again the KER population presents the lowest values.

P. radiata from Tunisia (KER) present significant differences (p<0,001) from all the other sites and have the lowest values for total weight. At the other end, animals from Saronikos Gulf (SA2) (weight measurements from SA1 were not available) have the greater values. SA2 population is significantly different from all other sites except Rodos (ROD).

- Convexity in SA1, SA2 and LAT present the higher values. Pinctada radiata in ROD and KER is the less convex.

-The variations of Dorsal Side are not statistically linked to the other morphologic parameters. DS is a parameter highly influenced by the ecological conditions. The variations of this parameter are significant for only a couple of sites: SA1 and KER. The first site presents the more important value of R whereas KER, as for the other parameters, presents the lowest one. This indicates an almost equal increase for the two parameters in the Tunisian population while at the other sites height has a faster growth rate than DS.

DendrogramFurthest Neighbor Method,Euclidean

Dis

tan

ce

0

1

2

3

4

5

6

SA

1

KE

R

LA

T

RO

D

SA

2

DendrogramFurthest Neighbor Method,Euclidean

Dis

tan

ce

0

1

2

3

4

5

6

SA

1

KE

R

LA

T

RO

D

SA

2

• Aloui - Bejaoui N., M. Le Pennec, S. Rezgui & F. Maamouri, 2003 –Influence du cycle de reproduction et des conditions du milieu sur la croissance pondérale de Mytilus galloprovincialis basée sur l’utilisation d’un animal standard. Marine life, 12 (1-2): 47-57 • As-Sayed H, El-Din AKG & Saleh KM, 1997- Shell morphometrics and some biochemical aspects of the pearl oyster Pinctada radiata (Leach 1814) in relation to different salinity levels around Bahrain. Arab Gulf Journal Of Scientific Research 15 (3): 767-782.• Box G.E.P. & Cox D.R., 1982 - An analysis of transformations revisited, rebutted. Journal American Statistical Association 77: 209-210. • Dagnélie P., 1982 - Théories et méthodes statistiques. Applications agronomiques. Vol. I et II. Nouvelle édition. Presses Agronomiques de Gembloux. 463 p

• Hynd J.S., 1955 – A revision of Australian pearl –shells, genus Pinctada (Lamellibranchia) – Australian journal of marine and freshwater research, vol 6 n°1 : 98-132. • Oliverio M., Gerosa G. &cocco M., 1992 – First record of Pinctada radiata (Bivalvia, Pteriidae) épibionte on the loggerhead turtle Caretta . Boll. Malac.,28(5-12):149-152• Serbetis C.D. 1963 - L'acclimatation de Meleagrina (Pinctada) margaritifera (Lam.) en Grèce - Rapport Commission Internationale de la Mer Méditerranée, 17(3): 271-272. • Zenetos A. S. Gofas, G. Russo & J. Templado 2003 - CIESM Atlas of Exotic Species in the Mediterranean Sea, vol. 3 Molluscs. CIESM, Monaco. (www.ciesm.org/atlas), 376 p.• Zouari TS. & Zaouali J., 1994 - Reproduction de Pinctada radiata (Leach, 1814, Mollusque, Bivalve) dans les iles Kerkennah (Tunisie). Marine Life, Marseille, 4(1): 41-45.

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conclusion

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