Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia)

Helgoland Marine Research, Sep 2014

Relative growth and the reproductive cycle of the date mussel Lithophaga lithophaga were studied from September 2002 to October 2003 in the Bizerte Bay (Northern Tunisia). Relationships between shell length and shell width, shell height as well as volume-related variables (shell dry weight, soft tissues dry weight and total wet weight) showed negative allometries in both sexes except for shell width in males (isometry) and shell height in both sexes (positive allometry). The sex ratio was unbalanced, within the length range of 6–48 mm, 49.43 % of the animals were males, 24.39 % females and 26.17 % sexually undifferentiated; within the length range of 49–92 mm, the respective values were 41.19, 52.7 and 6.1 %. Histological investigations as well as analyses of the condition index and the gonadosomatic index (CI and GSI) revealed the presence of a single reproductive cycle per year. Spawning occurred at the end of August and early September and was associated with a decrease in seawater temperature and salinity. A resting phase occurred in winter, coinciding with the lowest water temperatures. Histological examinations of the gonads of a total of 130 specimens revealed only two cases of hermaphroditism. The present study constitutes a useful baseline for a sustainable management of local wild stocks of L. lithophaga.

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Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia)

Helgol Mar Res Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia) Ferdaous Jaafar Kefi 0 1 2 Samir Boubaker 0 1 2 Najoua Trigui El Menif 0 1 2 0 S. Boubaker Laboratory of Human and Experimental Pathology, Pasteur Institute of Tunis , 13 Place Pasteur, 1002 Tunis , Tunisia 1 F. J. Kefi (&) N. T. E. Menif Laboratory of Environment Bio-monitoring, Faculty of Sciences of Bizerte, University of Carthage , 7021 Zarzouna, Bizerte , Tunisia 2 Communicated by H.-D. Franke Relative growth and the reproductive cycle of the date mussel Lithophaga lithophaga were studied from September 2002 to October 2003 in the Bizerte Bay (Northern Tunisia). Relationships between shell length and shell width, shell height as well as volume-related variables (shell dry weight, soft tissues dry weight and total wet weight) showed negative allometries in both sexes except for shell width in males (isometry) and shell height in both sexes (positive allometry). The sex ratio was unbalanced, within the length range of 6-48 mm, 49.43 % of the animals were males, 24.39 % females and 26.17 % sexually undifferentiated; within the length range of 49-92 mm, the respective values were 41.19, 52.7 and 6.1 %. Histological investigations as well as analyses of the condition index and the gonadosomatic index (CI and GSI) revealed the presence of a single reproductive cycle per year. Spawning occurred at the end of August and early September and was associated with a decrease in seawater temperature and salinity. A resting phase occurred in winter, coinciding with the lowest water temperatures. Histological examinations of the gonads of a total of 130 specimens revealed only two cases of hermaphroditism. The present study constitutes a useful baseline for a sustainable management of local wild stocks of L. lithophaga. Lithophaga lithophaga; Hermaphroditism; Growth; Reproductive cycle; Bizerte Bay Introduction Rock-boring bivalves are an important component of rocky marine ecosystems (Guidetti and Boero 2004; Devescovi et al. 2005) . The endolithic bivalve Lithophaga lithophaga (Linnaeus 1758) is part of this community, digging into limestone by means of chemical secretions (Morton and Scott 1980; Mojetta and Ghisotti 1996; Owada 2009) . In their tunnels, individuals can live for 50 years or more (Katsanevakis et al. 2008). This gonochoristic bivalve is most abundant in the midlittoral and sublittoral zones (Galinou-Mitsoudi and Sinis 1994) . The species is distributed along Atlantic coasts from Portugal to Senegal and further to the north of Angola (Gonzalez et al. 2000) . Furthermore, it occurs throughout Mediterranean coasts (Fischer et al. 1987; Gonzalez et al. 2000) .During the last decades, L. lithophaga has been intensively exploited in some European countries such as the former Yugoslavia and Spain (Poutiers 1987), and also in parts of the Moroccan Mediterranean coast (Shafee 1999) . Due to the species’ organoleptic quality and thus extremely high price (Devescovi 2009) , it is often collected and sold even where this is inhibited by law (Devescovi and Ivesˇa 2008) . In Italy, for example, L. lithophaga is greatly appreciated as seafood, reaching a commercial value of up to 60 €/kg (FAO 2004) . Illegal harvesting causes significant environmental damage (Gargominy et al. 1999) , affecting fish population dynamics and rocky reef ecosystem functioning with a significant local decrease in species richness and abundances (Fraschetti et al. 2001; Guidetti et al. 2002, 2003; Guidetti and Boero 2004) . In this context, Guidetti et al. (2003) have assessed the distribution patterns of two species of sea urchins, Paracentrotus lividus (Lamarck 1816) and Arbacia lixula (Linnaeus 1758), and barren habitats (coralline barrens and bare substrates) in rocky reefs impacted by the destructive fishery for L. lithophaga (SW Apulia, Italy). Their results showed that the date mussel fishery may have the potential to affect distribution patterns of sea urchins and to greatly enhance the percent cover of barren grounds in shallow Mediterranean rocky reefs. The restoration of communities destroyed during the extraction of L. lithophaga is very slow and often impossible due to the fact that this species is rather long-lived with a growth rate which is one of the slowest among bivalves (Katsanevakis et al. 2008) . The date mussel was subject of several studies dealing with its biology, population dynamics, fecundity and habitat (Sˇ imunovic´ et al. 1990; Galinou-Mitsoudi and Sinis 1994, 1995, 1997; Jaafar Kefi et al. 2007; Devescovi 2009) . Some other studies focused on the impact of harvesting and overexploitation on marine ecosystem and Mediterranean rocky coasts (Fanelli et al. 1994; Parravicini et al. 2009) . Besides the important ecological role of L. lithophaga in recent ecosystems, its fossils have been used in paleoecological and paleo (...truncated)


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Ferdaous Jaafar Kefi, Samir Boubaker, Najoua Trigui El Menif. Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia), Helgoland Marine Research, 2014, pp. 439-450, Volume 68, Issue 3, DOI: 10.1007/s10152-014-0400-9