Sulfide influence on metal behavior in a polluted southern Mediterranean lagoon: implications for management

The degree of pyritization and degree of trace metal pyritization (DTMP) were investigated in sediments from Ghar El Melh Lagoon (northern Tunisia) in order to study metal deposition. A sediment core and 28 samples were thus taken in summer 2008, and metals and sulfate were analyzed in pore water/pyrite. Acid-volatile sulfide and metals were simultaneously extracted from these two fractions and the role of pyrite in the metal cycling studied. To examine pyrite presence and mineralogical form in sediments, X-ray diffraction of the washed and decarbonated sediment was performed along with scanning electron microscopy. Results showed that pyrite is present in fromboidal and euhedral forms. Thermodynamic calculation highlighted the formation of metallic sulfides and the co-precipitation of metals with iron sulfides. The DTMP increases with depth, indicating that these metals are either sequestered as sulfides or that they co-precipitate with pyrite into the deep sediment.

Factors driving the seasonal distribution of zooplankton in a eutrophicated Mediterranean Lagoon

The distribution of the zooplankton community was studied along with environmental factors at five sampling stations in Ghar El Melh Lagoon (GML) (Mediterranean Sea, northern Tunisia). GML is characterized by specific following properties: broad and shallow, freshwater supply (Station 1); connection to the sea (S2); stagnation (S3 especially), and eutrophic conditions with enhanced nutrient concentrations (S4 and S5). Samples were taken twice monthly from February 2011 to January 2012. Twenty-three zooplankton groups comprising 10 larval stages were identified. Zooplankton assemblages were largely dominated by copepods (37.25%), followed respectively by ciliates (21.09%), bivalve larvae (14.88%) and gastropod veligers (12.53%). Redundancy analysis indicated that while no significant difference was found in the distribution of zooplankton at any station, a strong difference was observed according to season. Both temporal and physicochemical fluctuations explain more than 50% of changes in zooplankton abundances.

(Myxozoa, Myxosporea) parasite of Solea solea (L.) (Pleuronectiformes, Soleidae) from Ghar El Melh Lagoon, Tunisia

A new Myxosporea, Zschokkella soleae sp. n., was found in the gall bladder and the bile of common sole, Solea solea (L.), from Ghar El Melh Lagoon in north-east Tunisia. This is the first record for the presence of Zschokkella species in Tunisian waters. The parasite's plasmodia are polysporic with variable size and shape. Some plasmodia appeared attached to the gall bladder epithelium while others were found free in bile. Mature spores are ellipsoidal in frontal view 13.8±0.38 μm long and 10.86±0.40 μm wide with two equal size spherical polar capsules 3.6±0.43 μm in size. The prevalence of infection seems to correlate with host size and changes over the year with maximum percentage in summer. Based on the 18S rDNA sequence data, Z. soleae sp. n. is readily distinguishable from other myxozoan DNA sequences in GenBank. Phylogenetically, the new species is placed in the freshwater Myxidium clade including several Zschokkella spp. infecting the gall bladder. Morphology, histology as well as DNA sequence analysis indicate that the examined species differs from all previously described Zschokkella species.

Factors driving the seasonal distribution of planktonic and epiphytic ciliates in a eutrophicated Mediterranean lagoon

We studied the distribution of planktonic and epiphytic ciliates coupled with environmental factors and microalgae abundance at five stations in Ghar El Melh Lagoon (Tunisia). Planktonic ciliates were monitored for a year and epiphytic ciliates were sampled during summer 2011 in concordance with the proliferation of the seagrass Ruppia cirrhosa. Ciliate assemblage was largely dominated by Spirotrichea followed respectively by Tintinnida of and Strombidiida. No significant difference was found in the distribution of ciliate species among the stations. Redundancy analysis indicates that abiotic factors (temperature and nutriments) have a significant effect on the dynamics of certain ciliates. For epiphytic ciliates, 4 species were identified: Tintinnopsis campanula, Aspidisca sp., Strombidium acutum and Amphorides amphora. Based on PERMANOVA analyses, ciliates exhibit significant correlations among months and stations. According to ACP, epiphyte distribution follows roughly those of R. cirrhosa and pH. Significant correlations were found between harmful dinoflagellates and both planktonic and epiphytic ciliates.