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)