Located in the Southern Eastern Tunisia, with an arid to semiarid
climate, the Gulf of Gabes (NE Mediterranean, 33N and
35N) not only covers the most Tunisian prolific fish-producing
area, but also shelters several stations for collecting seashells
along its shores, as well as being a famous habitat for marines
turtles (Baran and Kasparek, 1989; Maffucci et al., 2006). Despite
its economic and wildlife conservational importance this Gulf is
now strongly under stress from industrial activities, tourism and
recreation (Hamza-Chaffai et al., 1997; Smaoui-Damak et al., 2003,
2006). A few studies have been conducted in the Gulf of Gabes
focussing on the seasonal plankton food web structures such as
the summer phytoplankton bloom (Bel Hassen et al., 2008; Drira
et al., 2008) and copepod distribution (Drira et al., in press), but
data on the distribution on a large scale of ciliate assemblages are
lacking. In recent years, interest in the ecological role of marine
planktonic ciliates has increased, and their importance in energy
transfer within food webs has been emphasized (Fenchel, 1988).
Ciliate abundance in marine environments are under the control
of zooplankton, particularly filter-feeding copepods (Lampert
et al., 1986; Atkinson, 1996) as well as in the laboratory (Hartmann
et al., 1993; Pe´ rez et al., 1997). On the other hand, several
findings have provided evidence that ciliates are important
grazers on nanoplankton and bacterioplankton (Simek et al., 1997;
Premke and Arndt, 2000). The study of the dynamics of ciliate
species composition and standing stocks should thus provide
valuable information on the functioning of aquatic ecosystems.
Such studies are well documented in freshwater ecosystems
(Beaver and Crisman, 1989; Aleya et al., 1992) and the western
Mediterranean (Dolan and Marrase´ , 1995; Pe´ rez et al., 2000;
Balkis, 2004) but are lacking for the northern eastern Mediterranean
particularly along the nearshore of the Gulf of Gabes
where more than 20 stations for collecting seashells are identified
(Hamza-Chaffai et al., 1999). This area is currently undergoing
extensive changes due to natural factors including sediment
supply, sea-level rise and Sabkhas interference. Sabkha is an
Arabic term for a coastal and inland saline mud flat built up by
the deposition of silt, clay and sand in shallow, sometimes
extensive, depressions (Warren, 2006). It is noteworthy that the majority of studies on the ciliate community structure dealt with
true plankton communities while very shallow coastal locations
were poorly investigated. To our knowledge, there is no data on
ciliates neither in very shallow coastal waters (<1 m depth) nor in
the very shallow coastal waters that are submitted to Sabkha
influence. In this context, it is important to start a survey of the
protistan populations of this complex coastal region by answering
to questions, such as what ciliates live here? Which types are
numerically most important? Are there consistent seasonal variations?
Addressing these questions may offer an opportunity to
emphasize the importance of protozoa communities for the
nearshore ecosystems, since their pelagic/benthic interface are
likely to be complex with regenerated nutrients released from the
sediment when disturbed (Verney et al., 2007). The aim of the
work reported here is to explore the seasonal dynamics of ciliate
assemblages and biomass and their relationships with environmental
factors at three stations serving for collecting seashells
along the coast of the Gulf of Gabes. These stations were likely to
be significant sites because the first station is less influenced by
the southern arid conditions than both the second, which is the
subject of intense marine traffic inducing pollution (Drira et al.,
2008) and the third station which is the saltiest as surrounded by
a saline area called the Meider Sabkha.
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