Macrozoobenthic species composition and distribution in the Northern lagoon of Tunis

1 - The macrobenthic community and abiotic parameters of a Méditerranean lagoon (Norhern lagoon of Tunis) was studied on automnal season during 1995, 1996 and 1997. 2 - Analysis of abiotic parametters revealed significant differences between stations. Variations of temperaturs and salinity reported in this studie show a gradient increasing in the direction circulating currents. Tidally driven marine waters cause a contnuous refreshment of lagoon waters, thus promoting oxygenation and nutrient loading. 3 - In total, 61 species were recognized, divided into seven zoo-goups with Molluscs always dominant. A noticeable increase in specific richness occured due to hydrologic and environmental improvement after sanitation in 1984-1988. 4 - Comparison of ecological indexes (specific richness, abundances, density, Shannon- Weaver indexes and evenesses) indicate significant variations in the spatial distribution and structure of benthic community, area A subjected to marine refreshment having a more deversified benthic fauna. In contrast, stations (B and C) remote from the sea display a neat faunal disturbance. 5 - Multivariate analysis help characterize hetergeneity in the benthic community structure of stations; thus, Echinodermata and Porifera phyla represent a great heterogeneity in species abundances. 6 - Physico-chemical properties of lagoon waters and macrobenthic faunal characters help identify three main sectors: i) a northeastern sector near the lagoon entrance, with newly introduced marine species (as Pinctada radiata); ii) a transitional sector which suffered pollution earlier to lagoon sanitation; iii) a sector with confinement and typically lagoonal, eurythermal and euryhaline specie

Associated fauna of the fan shell <em>Pinna nobilis</em> (Mollusca: Bivalvia) in the northern and eastern Tunisian coasts

Epifaunal communities associated with the fan shell Pinna nobilis Linnaeus, 1758 along the Tunisian coastline were investigated. Both univariate and multivariate analysis were done at different spatial scales within five populations located at different localities, three from northern and two from eastern Tunisia. The size of Pinna did not appear as the main factor affecting the structure of the associated biota, which seemed to be more influenced by (a) marine-lagoon and (b) biogeographic gradients. Patterns of similarity of sessile sclerobionts and motile epifauna were clearly different. The former assemblage best replied to lagoon-sea gradient and to locality, with three real clusters at 40%, whereas the latter assemblage scattered widely in a non-metrical MDS plane, with two real clusters only at 20% similarity. The spatial turnover of motile species was ten times higher than that of sessile species at a small spatial scale, being less affected by Pinna size, and three times higher though invariant at a large geographic scale. On the other hand, β-diversity of sessile species appeared to be more influenced by latitudinal (climatic) gradient at a large scale, being higher in the northern than in the eastern communities. Analysis of taxonomic (dis)similarity of the whole community detected these two sources of environmental (lagoon-sea gradient) and biogeographic (lati-longitudinal gradient) variation, although each phylum showed its peculiar pattern. In terms of Dajoz's constancy index the majority of associated communities were dominated by rare species, and within the majority of epifaunal assemblages, the most abundant sessile epizoobiont was a bivalve mollusc. The sessile epifauna was dominated by active filterers, which led to a possible existence of trophic competition between the host and the sedentary epizoites, since both basibionts and sclerobionts occupy the same trophic niche. The fan shell played an important ecological role, providing new hard substrate to colonise, increasing the spatial heterogeneity for the surrounding soft-bottom communities, and contributing to the overall increase of the local biotope complexity level

First data on genetic diversity of the small pearl oyster Pinctada Radiata (Leach, 1814) in Mediterranean populations by means of the mitochondrial COX1 marker

This study gives a first molecular insight into the genetic structure of Pinctada radiata by analysing a mitochondrial DNA marker in four South -Central Mediterranean populations of this lessepsian bivalve. Specimens were collected from four central Mediterranean locations. Six polymorphic sites were found, defining seven haplotypes. Haplotype and nucleotide diversity values were low to moderate. The low levels of within -population genetic diversity detected in the present study are consistent with a scenario of founder effect, as expected for an invasive species. The shallow genetic structuring among the sampled populations may result from two factors – long larval duration which promotes the homogenization of the genetic pool through an effective gene flow or the current populations may not have had enough time to differentiate.peer-reviewe

Integrated Biomarker Response for Environmental Assessment Using the Gastropod Phorcus turbinatus along the Northern and the Northeastern Coasts of Tunisia

This work aims to assess the spatial and temporal variations of four biomarkers activities and to integrate their biological responses in a battery using the gastropod Phorcus turbinatus. The monitoring was carried out during the period between April 2014 and January 2015 at six stations along the northern and the northeastern coasts of Tunisia. The Fulton condition factor was estimated and the activities of catalase, acetylcholinesterase and glutathione-S-transferase were evaluated by spectrophotometry. A multi-biomarker battery approach was used to assess ecosystems’ condition and to identify environmental impacts on the organisms. The results suggest that the enzymatic activities of CAT and GST depend especially on seasons. As for AChE activity, it was similar between seasons and stations. The values of the integrated biological response were maximal at Jarzouna in summer and at Sidi Daoued in winter, indicating the presence of severe stressors suffered by the organisms. This perturbation may be due to the enrichment of the waters by xenobiotics, namely polycyclic aromatic hydrocarbons, insecticides, phosphate wastes, PCBs and pesticides. Thus, P. turbinatus seems to be a good bioindicator of chemical pollution, constituting an adequate tool for a bio-monitoring program

Engineering effect of Pinna nobilis shells on benthic communities

Within the framework of the possibility of using the Mediterranean pen shell Pinna nobilis in restoration and conservation plans of benthic habitats, an in situ experiment was conducted using empty P. nobilis shells. The latter were transplanted in a bare soft-bottomed area and their associated fauna were followed along 120 days and compared at different temporal points and with the assemblages living in the surrounding soft-sediment area. Compared to soft-sediment communities, an evidently increasing succession of species richness, abundance, and diversity descriptors (Shannon-Wiener H′ and Pielou's evenness J′) was observed with the community inhabiting empty Pinna shells. Among the forty-five (45) species found in association with the transplanted empty shells, seventeen (17) were found constantly in the three temporal points; the other twenty-eight (28) species appeared in the samples collected in the second and/or third sampling time. While motile and sessile species associated to Pinna shells showed an increasing pattern of appearance and abundance along the experiment time, those of soft sediment remained almost constant. The comparison between Pinna shells and soft-sediment associated communities showed that the species richness was slightly different between the two different sample types (49 for soft sediment versus 45 for empty Pinna shells); however the total abundance was found more important with empty Pinna shells. The results obtained herein argue in favor of the important engineering effect of P. nobilis in soft benthic habitats and therefore for the necessity of its conservation

Characterization of microplastics in the surface waters of an urban lagoon (Bizerte lagoon, Southern Mediterranean Sea): Composition, density, distribution, and influence of environmental factors

International audienc

Microplastics in edible mussels from a southern Mediterranean lagoon: Preliminary results on seawater-mussel transfer and implications for environmental protection and seafood safety

International audienc