Combined effect of light intensity and glucose concentration on Arthrospira platensis growth and photosynthetic response was evaluated using a 3 2 factorial design. This design was carried out with light levels of 50, 100, and 150 µmol photons m −2 s −1 and glucose concentrations of 0.5, 1.5, and 2.5 gL −1 . Results from the response surface methodology were that the highest level of light intensity and glucose concentration improved biomass (1.33 gL −1 ), maximum specific growth rate (0.49 day −1 ), and net photosynthetic rate (139.89 µmol O 2 mg Chl −1 h −1 ). Furthermore, the interaction of both factors showed that at low light, glucose had a low effect on maximum biomass and maximal net photosynthetic rate. However, at the highest light levels, the effect of glucose was more sensitive and the increase of glucose concentration increased the levels of all responses. The rates of the instantaneous relative growth, net photosynthesis, and dark respiration of growth cultures showed two different phases in mixotrophic condition. The first was distinguished by the preponderance of the photoautotrophic mode; the second was based mainly on photoheterotrophy.
In Tunisia, Monastir bay, extending for 38 km along the eastern coast of Tunisia, harbors different species of bivalves such as the clam Ruditapes decussatus, a species of major socio-economic interest. Despite its importance, no studies have been carried out about the morphology of this mollusc in Monastir bay. Thus, the current study aimed to analyze the shell morphological variations in the European clam Ruditapes decussatus from Monastir Bay coast. The comparison of the shell shape of individuals from
HIGHLIGHTS• Ruditapes decussatus from four sites belonging to Monastir bay (Tunisia) was first time analyzed based on morphometry and comparative statistics.• The site of Ksiba was distinguishable from other sites by larger and heavier specimens.• The sub-trapezoidal shape was dominant with small-size classes, in most sites.• The principal component analysis (PCA) revealed different population groups, with two intrapopulation groups for Sokrine site.• Allometric relationships showed highly significant correlation with different growth patterns (positive allometric, negative allometric and isometric).
Microbial pollution in marine environments is one of the critical issues with regard to the sanitary status of recreational activities and seafood harvesting due to a potential contamination by pathogenic microorganisms. This review's objectives were to identify instances of bacterial, viral and protozoan parasite pollution in the Tunisian coastal region and to make recommendations for further research. Fecal indicators such as Coli and Salmonella spp were detected in samples of clams and mussels. Vibrionaceae species were also recorded in seawater, sediment, fish and clams in different sites from north to south with the dominance of Vibrio alginolyticus. Bivalve Escherichia mollusks collected from the Tunisian coast have been revealed to harbor viruses as well as protozoan parasites. Furthermore, the isolation of multidrug-resistant bacterial strains from Tunisian coastlines proves the significant spread and circulation of antibiotic-resistance caused by the massive use of antibiotics. In conclusion, we suggest intensive monitoring and cutting-edge wastewater treatment technologies to enhance seawater quality and preserve the biodiversity of aquatic life. Rapid detection techniques for the most important pathogenic microorganisms in seafood and seawater must be also developed to reduce human health risk.
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