No abstract

Marteilia refringens is a protozoan parasite recognized as a significant pathogen of the European flat oyster Ostrea edulis. The life cycle of this species is still poorly known, although there is evidence of the need for intermediate host(s). In the present study, we have used molecular approaches to identify this parasite in samples of the dwarf oyster Ostrea stentina after reports of massive mortality along the Tunisian coasts. In 2009 we evaluated the status of O. stentina from Monastir and checked if there was an infection with M. refringens, using polymerase chain reaction assays. Of the 103 tested O. stentina, 85 were PCR-positive using a Marteilia genus-specific assay. Additional assays were subsequently carried out on some samples collected in 2010 in Monastir and processed for histology, transmission electron microscopy and complementary molecular analyses. PCR was carried out to amplify the IGS and ITS regions. Histological and transmission electron microscopy analyses allowed us to confirm the presence of this parasite in the digestive gland tissue of O. stentina and to characterize it at the ultrastructural level. This is the first record of the occurrence of M. refringens in the oyster O. stentina along the Tunisian coasts.

The variability of shell morphology and relative growth of the invasive pearl oyster Pinctada radiata was studied within and among ten populations from coastal Tunisia using discriminant tests. Therefore, 12 morphological characters were examined and 34 metric and weight ratios were defined. In addition to the classic morphological characters, populations were compared by the thickness of the nacreous layer. Results of Duncan's multiple comparison test showed that the most discriminative ratios were the width of nacreous layer of right valve to the inflation of shell, the hinge line length to the maximum width of shell and the nacre thickness to the maximum width of shell. The analysis of variance revealed an important inter-population morphological variability. Both multidimensional scaling analysis and the squared Mahalanobis distances (D2) of metric ratios divided Tunisian P. radiata populations into four biogeographical groupings: the north coast (La Marsa); harbours (Hammamet, Monastir and Zarzis); the Gulf of Gabès (Sfax, Kerkennah Island, Maharès, Skhira and Djerba) and the intertidal area (Ajim). However, the Kerkennah Island population was discriminated by the squared Mahalanobis distances (D2) of weight ratios in an isolated group suggesting particular trophic conditions in this area. The allometric study revealed high linear correlation between shell morphological characters and differences in allometric growth among P. radiata populations. Unlike the morphological discrimination, allometric differentiation shows no clear geographical distinction. This study revealed that the pearl oyster P. radiata exhibited considerable phenotypic plasticity related to differences of environmental and/or ecological conditions along Tunisian coasts and highlighted the discriminative character of the nacreous layer thickness parameter.

The harbour area of Sidi Youssef in Kerkennah islands is characterized by specific anthropogenic pressures linked to fishing activities. To study the functional diversity of benthic macro-invertebrates, 10 stations located around the port and along the ship canal were sampled by SCUBA diving. Collected invertebrates were identified, counted and preserved. For the functional organization of the community, the most common biodiversity indices and functional groups were assessed at each station, and main physical and chemical parameters were measured. Results showed that the main apparent anthropogenic stress, that could lead to negative impacts on the studied area, was related to dredging/harbour activities. Suspension feeders, consisting essentially of polychaetes, which may be disturbed by water turbidity, dominated the stations farthest from the port, where the intensity of harbour activities is obviously reduced. On the contrary, carnivores dominated inside the port, possibly benefiting from fish-scraps discarded at the area, while stations close to the port appeared to be more balanced trophically. The applied biotic indices showed that the area is in good ecological status, except of the navigation channel and the port entrance, which were slightly degraded.

Gonad of the Mediterranean pectinid Flexopecten glaber was studied in order to describe the morphology and the ultrastructural characteristics of the mature spermatozoa. The spermatozoon has a 2.5 μm pyriform head and a 40–45 μm flagellum. The four mitochondria of the mid-piece are 0.6 μm in diameter. The nucleus contains dense chromatin fibres and possesses two depressions: a wide (0.19 μm) and deep (0.58 μm) sub-acrosomal one, and the other at the base of the head, less deep (0.36 μm) and less wide (0.12 μm). The objective was to situate this scallop in the phylogenetic diagrams found in the literature concerning the commercial pectinid species.

Mussel farming is the main economic activity in Bizerte Lagoon, with a production that fluctuates depending on environmental factors. In the present study, we apply a bioenergetic growth model to the mussel Mytilus galloprovincialis, based on dynamic energy budget (DEB) theory which describes energy flux variation through the different compartments of the mussel body. Thus, the present model simulates both mussel growth and sexual cycle steps according to food availability and water temperature and also the effect of climate change on mussel behavior and reproduction. The results point to good concordance between simulations and growth parameters (metric length and weight) for mussels in the lagoon. A heat wave scenario was also simulated using the DEB model, which highlighted mussel mortality periods during a period of high temperature.

This is the first study of the metabolic enzyme activity and energy state of the dwarf oysterOstrea stentina(Payraudeau, 1826) in Tunisia and in the Mediterranean region. The main purpose of this study was to examine the modulation of the physiological status of the oysterO. stentinadepending on the season and the presence of parasiteMarteilia refringens. The prevalence of bonamiosis and marteiliosis were established by PCR.Bonamia exitiosawas detected only in 2.91% of oysters while the prevalence ofM. refringenswas 100% (30 Ind./30) in February and 93.93% (28 Ind./30) in March. A 42–87% mortality rate was reported during the study period. Biochemical analyses were carried out to evaluate the management of the energy resources in regard to the biochemical changes of lipids and carbohydrates. The enzyme activity of pyruvate kinase (PK), citrate synthase (CS) and cytochrome c oxidase (CCO) were measured and the mean level of enzyme activity was respectively 20.31 mU mg−1protein; 12.06 mU mg−1protein and 3.59 mU mg−1protein. Carbohydrate contents ofO. stentinawere very low all year round with an average of 15.18% in dry weight, and lipid contents remain similar (11.77% in dry weight) compared with the values reported for most other temperate bivalves. Enzyme activity significantly decreased over time (P< 0.001). The energy resources of the oysterO. stentinawherein much of the energy was devoted to reproduction seem to affect the defence system.

Hammamet Marina is the most important touristic port in the Gulf of Hammamet (Tunisia). The present work is a contribution to the knowledge of the functional diversity and structure of the malacofauna community in this area. Three different stations (A, B and C) within the port were sampled seasonally for a year (2005)(2006). The mollusc assemblage studied was represented by 14 species (in totally 2669 ind. were found). Among the four mollusc classes recorded, bivalves were the best represented (73.76% of the total number species), followed by gastropods (22.02%), cephalopods (2.42%) and polyplacophores (1.80%). Atlanto-Mediterranean (42.85%) and Endemic Mediterranean (39.28%) taxa prevailed in the community, followed by Indo-Pacific (7.14%) and cosmopolitan species (3.57%). A clear spatial zonation was distinguished. The station B hosted the highest abundance of gastropods (309±19.92 ind. m -2 ) and a species richness of 6±0.40. The station station A hosted the most equilibrated trophic structure, with a higher bivalve abundance (1378±99.23 ind. m -2) and a species richness of 6±0.1. Station C, located close to the mooring boats, presented the lowest abundance (230±17.47 individuals m -2 ) and the most affected assemblage. This station seemed to be affected by the higher anthropogenic pressure assessed compared to the other two stations, mainly oil pollution, due to the large quantities of hydrocarbon discharged from the boats.