See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/286280734 Distribution, habitat and population densities of the invasive species Pinctada radiata (Molluca: Bivalvia) along the Northern and Eastern coasts of Tunisia Article in Cahiers de Biologie Marine · January 2009 CITATIONS READS 22 131 4 authors, including: Sabiha Tlig-Zouari Oum Kalthoum Ben Hassine University of Tunis El Manar University of Tunis El Manar 74 PUBLICATIONS 738 CITATIONS 287 PUBLICATIONS 1,940 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Congress participation View project Naturalists View project All content following this page was uploaded by Oum Kalthoum Ben Hassine on 16 November 2016. The user has requested enhancement of the downloaded file. Cah. Biol. Mar. (2009) 50 : 131-142 Distribution, habitat and population densities of the invasive species Pinctada radiata (Molluca: Bivalvia) along the Northern and Eastern coasts of Tunisia Sabiha TLIG-ZOUARI, Lotfi RABAOUI, Ikram IRATHNI and Oum Kalthoum BEN HASSINE Unité de recherche de Biologie, Ecologie et Parasitologie des Organismes Aquatiques. Campus Universitaire, Université Tunis El Manar, Faculté des Sciences de Tunis, Département de Biologie, 2092 Tunis - TUNISIE. Tel / Fax: (00216) 71881939, Mobile: (00216) 98 234 355. E-mail: [email protected] Abstract: The pearl oyster Pinctada radiata (Leach, 1814) is an alien species introduced to the Mediterranean Sea and recorded in Tunisia many years ago. However, since its record in Tunisian inshore areas, no studies have been carried out about the spread of this invasive mollusc. Thus, the status of this species is still poorly known and there is a knowledge- gap about its distribution and ecology. The present work is a contribution to the knowledge of the pearl oyster distribution and density of individuals along the northern and eastern Tunisian coasts, at depths situated between 0 and 6 metres. A large part of Tunisian coast was surveyed, stressing some observations concerning the species ecology and its preferred biotopes. The size structure of the five densest populations was also described. Pinctada radiata has not yet reached the northern coasts (Tabarka and Bizerta coasts). Density of individuals varied from one locality to another between 0 and 62.67 ± 6.11 individuals m-2. This mollusc prefers to be attached to vertical solid substrata (natural or artificial) within marine habitats with relatively high hydrodynamic conditions. Confined localities such as those inside lagoons seem not to be the preferred habitat for the proliferation of this immigrant species. Size structure analysis showed that the majority of the five examined populations, except for Tunis north lagoon and La Marsa, were dominated by large individuals exceeding 42 mm in shell height. It is worth noting that the maximum size (100.5 mm) recorded in the lagoon of Bizerta (Njila) is higher than that recorded in previous studies, in particular in its origin habitat (Red Sea). This suggests that Pinctada radiata is well adapt- ed to Tunisian coasts. Résumé : Distribution, habitat et densité des populations de l’espèce invasive Pinctada radiata (Mollusca : Bivalvia) le long des côtes septentrionales et orientales de Tunisie. L’huître perlière Pinctada radiata (Leach, 1814) est l’une des espèces exotiques de la Méditerranée. Elle a été signalée en Tunisie depuis plusieurs années. Toutefois, depuis son signalement sur les côtes tunisiennes, aucune étude n’a été menée sur ce mollusque invasif. Ainsi, le statut de cette espèce est encore mal connu et il existe un déficit de connaissances sur sa distribution et son écologie. Le présent travail est une contribution à la connaissance de la distribution de l’huître perlière et la détermination de sa densité le long des côtes nord et est de la Tunisie, à des profondeurs allant de 0 à 6 mètres. Une vaste partie de la côte tunisienne a été prospectée, en effectuant des observations sur l’écologie et les biotopes préférés par cette espèce. La structure en taille des cinq plus denses populations a également été décrite. Pinctada radiata ne semble pas encore franchir les côtes nord (les côtes de Tabarka et Bizerte). Sa densité varie d’une localité à une autre entre 0 et 62,67 ± 6,11 individus m-2. En outre, il semble que ce mollusque préfère être attaché à des substrats solides verticaux (naturels ou artificiels) dans des habitats soumis à des Reçu le 7 octobre2008 ; accepté après révision le 31 mars 2009. Received 7 October 2008; accepted in revised form 31 March 2009. 132 THE INVASIVE PEARL OySTER PINCTADA rADIATA AlONG TUNISIAN COASTS conditions hydrodynamiques relativement fortes. Les milieux confinés (localités intra-lagunaires) ne semblent pas être des habitats de prédilection pour la prolifération de cette espèce exotique. La majorité des cinq populations examinées, à l’ex- ception de la lagune nord de Tunis et de La Marsa, est dominée par de grands individus dont la coquille dépasse la hauteur de 42 mm. Il est à noter que la taille maximale (100,5 mm), enregistrée dans la lagune de Bizerte (Njila) est plus élevée que celle mentionnée dans des travaux antérieures, en particulier au niveau de son habitat d’origine (mer Rouge). Cela conduit à déduire que Pinctada radiata est bien adaptée sur les côtes tunisiennes. Keywords: Pinctada radiata l Invasive species l Bivalve l Distribution l Density l Mediterranean Sea l Habitat. Introduction Isles complex and in Kriti (Zenetos et al., 2007). Pinctada radiata was also intentionally imported for mariculture in The colonization of marine ecosystems by newly many areas of Greece and Italy during the last century. Up introduced species is a phenomenon that has begun to be to date, it has been recorded as common in the eastern more amplified, during the last decades. It seems to be Mediterranean with sporadic occurrences in the western favoured by various anthropogenic activities and the basin (Zenetos et al., 2003). Besides its adaptation to the current global warming (Quignard, 1994; Astraldi et al., subtropical environment of the south-eastern 1995). It has been stated that this phenomenon contributes Mediterranean, its tolerance to chemical contamination has to changing faunistic and floristic composition of the enhanced its expansion in enclosed polluted ecosystems colonized ecosystems and can then affect their ecological (Zenetos et al., 2007). equilibrium (Wolfe, 2002; Torchin et al. 2003). Introduced In Tunisia, the first records of Pinctada radiata was species are common in the marine environment because made by Bouchon-Brandely & Berthoule (1891) and Vassel organisms are easily transported via shipping routes and (1897), in the Gulf of Gabes (southern coast), where it had introduced unintentionally through aquaculture (Carlton, been confined and proliferated forming very dense 1996). In the Mediterranean Sea, biotopic colonization by populations (Zouari, 1985). In fact, outside the Gulf of exotic species has progressed and increased since 1970 Gabes, the presence of this bivalve is very sporadic along (Gofas & Zenetos, 2003). Thus, various exotic molluscan the eastern Tunisian coastline (Ktari-Chakroun & Azzouz, species have been recorded in different areas (Galil & 1971; Zouari, 1985; Tlig-Zouari, 1993). Research on Zenetos, 2002; Gofas & Zenetos, 2003; Zenetos et al., Pinctada radiata is very sparse and has been limited to the 2003). The Mediterranean Sea currently houses approxi- study of Kerkennah island populations (Tlig-Zouari, 1993). mately 139 exotic molluscs; among them ten species are Apart from some recent records in the inventories of locally invasive (Gofas & Zenetos, 2003; Zenetos et al., benthic macro-invertebrate communities (Diawara et al., 2005). The pearl oyster Pinctada radiata (Leach, 1814) 2008), no study has targeted the current distribution of this was among the first invasive immigrants that arrived to the species along the Tunisian coast and the density of its Mediterranean through the Suez Channel (Monterosato, populations in the habitats recently colonized. The study of 1878). Pinctada radiata is an epifaunal suspension feeder Pinctada radiata in Tunisia seems then to be important. of the subtidal zone and a fouling species, living attached The present study focuses on pearl oyster distribution on by its byssus to hard substrata. Usually it attains a length of the northern and eastern coasts of Tunisia, on the 50-65 mm, but may exceed 100 mm in length. It is a characteristics of colonized habitats, and on the protandric hermaphrodite species with sex inversion demographic structure of its populations. occurring in shells of 32-57 mm length. Gonad maturity is controlled by temperature (Tlig-Zouari & Zaouali, 1994). Material and Methods This indo-pacific bivalve has successfully spread through- out the Mediterranean colonizing continually new habitats In the present study, systematic surveys were carried out in the eastern basin (Tlig-Zouari & Zaouali, 1994 & 1998; along the coastal region from Tabarka to Monastir. Galil & Zenetos, 2002; Gofas & Zenetos, 2003; Zenetos et Observations were made during spring 2005 (March and al., 2005) and also in the Adriatic (Vio & De Min, 1996) April 2005) at 31 stations belonging to six sectors from the and Croatia (Doğan & Nerlović, 2008). Recently, it was northern and eastern Tunisian coastline (Fig. 1 & Table 1). recorded in newly invaded Hellenic sites, e.g. the Kyklades A total of 50 surveys were conducted by SCUBA diving, S. TLIG-ZOUARI, L. RABAOUI, I. IRATHNI, O.K. BEN HASSINE 133 Figure 1. Pinctada radiata. Study area sampling stations. 1. Ancient Tabarka harbour. 2. Tabarka El Corniche beach. 3. Tabarka Island. 4. Negro Cape. 5. Sidi Mechreg. 6. Serrat Cape. 7. Enjlaa Cape. 8. Blanc Cape. 9. Bizerta El Corniche beach. 10. Sidi Salem beach. 11. Rimel beach. 12. Bizerta channel. 13. Carrier Bay. 14. Njila. 15. Menzel Jemil. 16. Ghar Elmelh Lagoon. 17. Kalaat Landalous beach. 18. La Marsa beach. 19. The entrance lock of Tunis north lagoon-Kheireddine side. 20. Entrance lock of Tunis north lagoon-lagoon side.