Bizerte Lagoon Research Articles

Detection of Extended-Spectrum β-Lactamases (ESBL) Producing Enterobacteriaceae from Fish Trapped in the Lagoon Area of Bizerte, Tunisia.

Extended-spectrum β-lactamase and their molecular mechanism in Enterobacteriaceae were analyzed in 126 fish samples of 9 various wild species, living in the lagoon of Bizerte in Tunisia. Fifty-nine (59) Gram-negative strains were isolated and identified as Escherichia coli (n = 24), Klebsiella pneumonia (n = 21), Citrobacter freundii (n = 8), and Shigella boydii (n = 6). Forty-seven ESBL producers were identified using the synergic test. β-Lactamase genes detected were blaCTX-M-1 (E. coli/15; K. pneumonia/8; C. freundii/1; Sh. boydii/1), blaCTX-M-1+ blaOXA-1 (E. coli/4; K. pneumonia/3), blaCTX-M-1+ blaTEM-1-a (K. pneumonia/2), blaCTX-M-15+ blaTEM-1-a (K. pneumonia/1; Sh. boydii/1), blaCTX-M-15+ blaOXA-1 (K. pneumonia/1), blaCTX-M-15 (E. coli/3; K. pneumonia/1; Sh. boydii/3), and blaCTX-M-9 (C. freundii/3). Most strains (84.7%) showed a multiresistant phenotype. qnrA and qnrB genes were identified in six E. coli and in ten E. coli+one K. pneumonia isolates, respectively. The resistance to tetracycline and sulfonamide was conferred by the tet and sul genes. Characterization of phylogenic groups in E. coli isolates revealed phylogroups D (n = 20 strains), B2 (n = 2), and A (n = 2). The studied virulence factor showed prevalence of fimA genes in 9 E. coli isolates (37.5%). Similarly, no strain revealed the three other virulence factors tested (eae, aer, and cnf1). Our findings confirmed that the lagoons of Bizerte may be a reservoir of multidrug resistance/ESBL-producing Enterobacteriaceae. This could lead to indisputable impacts on human and animal health, through the food chain.

Occurrence of Halogenated and Organophosphate Flame Retardants in Sediments and Eels (Anguilla anguilla) From Bizerte Lagoon, Tunisia

Contamination by classic (polybromodiphenyl ethers, PBDEs) and emerging halogenated flame retardants (HFRs) like pentabromobenzene (PBEB), hexabromobenzene (HBB), decabromodiphenyl ethane (DBDPE ) and halogenated norbornenes (HNs), as well as organophosphate flame retardants (OPFRs) were investigated in sediment and eel (Anguilla Anguilla) samples from Bizerte Lagoon, northern Tunisia. This is the first time that OPFR levels have been reported in this area, showing higher concentrations than HFRs: from 9.77 to 164 ng/g dry weight (dw) and from 19.7 to 2154 ng/g lipid weight (lw) for sediment and eel samples, respectively. As regards HFRs, concentrations ranged from 3.30 to 28.5 ng/g dw in sediments and from 4.72 to 151 ng/g lw in eels. The relationship between OPFR and HFR concentrations in sediment and total organic content (TOC) was examined. Results suggested that OPFR levels were significantly correlated with TOC, whereas no correlation was found for HFRs and TOC. The study of potential health risks by eel consumption suggested that there is no significant human health risk associated with the dietary intakes for PBDEs.

Population dynamics and predatory impact of the alien jellyfish Aurelia solida (Cnidaria, Scyphozoa) in the Bizerte Lagoon (southwestern Mediterranean Sea)

Understanding the life cycle strategies and predatory impact of alien jellyfish species is critical to mitigate the impact these organisms may have on local populations, biodiversity, and ultimately on the functioning of food webs. In the Mediterranean Sea, little is known about the dynamics of alien jellyfish, although this area is a biodiversity hotspot and one of the most threatened by an increasing number of alien jellyfish. Here, we investigated the population dynamics and predatory impact of a non-indigenous scyphomedusa, Aurelia solida Browne 1905, in the Bizerte Lagoon, Tunisia. The study was based on a bimonthly survey performed over two consecutive years, from November 2012 to August 2014. Field observations showed that the planktonic phase of A. solida occurs from winter to early summer. Prey composition was investigated by means of gut content and field zooplankton analyses. Calanoid copepods, mollusc larvae and larvaceans represented the main food items of A. solida. To determine the jellyfish feeding rate and their predatory impact on zooplankton populations, the digestion time for zooplankton prey was assessed at three different temperatures: 13, 18 and 23 °C in laboratory conditions, corresponding to the average range of temperatures encountered by A. solida in the Bizerte Lagoon. We found that A. solida consumed 0.5–22.5% and 0.02–37.3% of the daily zooplankton standing stock in 2013 and 2014, respectively. These results indicate a non-negligible but restricted seasonal grazing impact on some mesozooplankton groups, explained by the relatively short lifespan of the medusa stage (5–6 months).

Trace elements and oxidative stress in the Ark shell Arca noae from a Mediterranean coastal lagoon (Bizerte lagoon, Tunisia): are there health risks associated with their consumption?

The current study examined the concentrations of ten trace elements (TE) (nickel, chromium, cadmium, iron, zinc, manganese, aluminum, copper, selenium and lead) in the edible tissue of the Ark shell Arca noae (L. 1758) from a Mediterranean coastal lagoon, the Bizerte lagoon during 2013-2014. The analysis of several redox status biomarkers, metallothioneins (MTs), malondialdehyde (MDA), glutathione peroxidase (GPx), reduced glutathione (GSH) and acetylcholinesterase (AChE), was monitored as a response to TE bioaccumulation and environmental parameters variability. Significant differences (p < 0.05) were observed between mean seasonal TE concentrations in A. noae soft tissue. The highest TE concentrations in A. noae soft tissues were recorded during summer, which coincided with the increase of body dry weight (BDW) and the gonad index (GI). During this season, biomarker responses were enhanced, revealing significant increases of MTs, MDA and GSH levels as well as GPx activity in A. noae tissues, while a decrease of AChE activity was observed. The levels of TE analyzed in A. noae and several parameters used to assess the potential human risk (estimated weekly intake, target hazard quotient and target hazard risk) were lower than the permissible limits for safe seafood consumption. Consequently, this shellfish can be considered safe for human consumption. This preliminary study presents prospects for the valorization of this seafood product in Tunisia's food sector. It also gives basal information for future environmental assessment studies in which A. noae could be used as early warning tools in the field of biomonitoring programs and confirms the usefulness of biomarkers to monitor the health status of aquatic organisms.

Legacy and Emerging Brominated Flame Retardants in Bizerte Lagoon Murex (Hexaplex Trunculus): Levels and Human Health Risk Assessment.

Occurrence of traditional (PBDEs) and novel (HBB, PBEB, DBDPE) brominated flame retardants, as well as the natural compounds of MeO-PBDEs, were studied in a shellfish species (Hexaplex trunculus) sampled from Bizerte Lagoon. PBDE and MeO-PBDE mean concentrations in murex soft tissues were 187 and 264ngg-1lw respectively. The alternative flame retardants were not identified. The sum of PBDE and MeO-PBDE levels recorded in murex from the investigated aquatic ecosystem were comparable or a relatively lower than those reported for other organisms from other regions across the world. The amount of PBDE and MeO-PBDE concentrations from the Bizerte Lagoon recorded in murex were comparable or a relatively lower than those recorded from other areas across the world for other species. There is not a danger to the population health with regard to PBDE intakes associated with the consumption of murex in Bizerte city. We believe that this is the first study of the analysis of these pollutants in marine gastropod mollusks from Tunisian aquatic areas.

Chronic ecotoxicity of ciprofloxacin exposure on taxonomic diversity of a meiobenthic nematode community in microcosm experiments

A laboratory bioassay was performed to assess the ecotoxicity of ciprofloxacin on a meiobenthic nematodes community from Bizerte lagoon (NE Tunisia). Four ciprofloxacin doses [D1 (50 µg/g), D2 (100 µg/g), D3 (200 µg/g), and D4 (500 µg/g)] were applied to the substrate, and responses were studied after one month. Discernible differences were observed between control assemblages and those populating ciprofloxacin treated substrates. All univariate indices were affected significantly compared to those in the control microcosm with increasing antibiotic concentration. The non-parametric Multi-Dimensional Scaling based on species abundances (MDS) showed significant separation of the control microcosm from the antibiotic-treated populations. The nematode species responses to the fluoroquinolone treatments varied: Odontophora villoti was reduced at all concentrations of ciprofloxacin and was considered “sensitive,” whereas Metoncholaimus pristiurus was affected by moderate concentrations; its abundance increased with the highest dose D4 and was described as “opportunistic.” Paramonohystera pilosa, whose abundance increased with antibiotic doses appeared “resistant.”

Inventory and new records of benthic amphipods from macrophytes and fine sand communities of the Bizerte lagoon (Tunisia, SW Mediterranean Sea)

Shallow water benthic communities from the Bizerte lagoon (northern Tunisia) were investigated at 33 stations sampled in April and July of 2016 and 2017. A total of 18 amphipod species were recorded among which two new species were recorded: one for Tunisian coasts (Jassa marmorata) and a second one for the Mediterranean Sea (Serejohyale spinidactylus). In addition, and compared to previous studies, nine amphipod species were collected for the first time in this lagoon. Amphipod assemblages were numerically dominated by the families Melitidae (28%), Caprellidae (14.5%) and Ampithoidae (11.7%). Three species: Cymadusa filosa, Dexamine spinosa and Elasmopus rapax were numerically dominant. According to their biogeography, most of the recorded amphipod species (11–18) showed an Atlantic–Mediterranean distribution, whereas four were cosmopolitan and three lessepsian Indo-Pacific migrants, but no species were Mediterranean endemic. Specimens of both Jassa marmorata and Serejohyale spinidactylus are illustrated and described.

Occurrence of epibenthic dinoflagellates in relation to biotic substrates and to environmental factors in Southern Mediterranean (Bizerte Bay and Lagoon, Tunisia): An emphasis on the harmful Ostreopsis spp., Prorocentrum lima and Coolia monotis

Harmful events associated with epibenthic dinoflagellates, have been reported more frequently over the last decades. Occurrence of potentially toxic benthic dinoflagellates, on the leaves of two magnoliophytes (Cymodocea nodosa and Zostera noltei) and thalli of the macroalgae (Ulva rigida), was monitored over one year (From May 2015 to April 2016) in the Bizerte Bay and Lagoon (North of Tunisia, Southern Mediterranean Sea). The investigated lagoon is known to be highly anthropized. This is the first report on the seasonal distribution of epibenthic dinoflagellates hosted by natural substrates, from two contrasted, adjacent coastal Mediterranean ecosystems. The environmental factors promoting the development of the harmful epibenthic dinoflagellates Ostreopsis spp., Prorocentrum lima and Coolia monotis were investigated. The highest cell densities were reached by Ostreopsis spp. (1.9 × 103 cells g−1 FW, in October 2015), P. lima (1.6 × 103 cells g−1 FW, in June 2015) and C. monotis (1.1 × 103 cells g−1 FW, in May 2015). C. nodosa and Z. noltei were the most favorable host macrophytes for C. monotis (in station L2) and Ostreopsis spp. (in station L3), respectively. Positive correlations were recorded between Ostreopsis spp. and temperature. Densities of the epibenthic dinoflagellates varied according to the collection site, and a great disparity was observed between the Bay and the Lagoon. Maximum concentrations were recorded on C. nodosa leaves from the Bizerte Bay, while low epiphytic cell abundances were associated with macrophytes sampled from the Bizerte Lagoon. The observed differences in dinoflagellate abundances between the two ecosystems (Bay-Lagoon) seemed not related to the nutrients, but rather to the poor environmental conditions in the lagoon.

The induced damage in the hepatopancreas of Orchestia species after exposure to a mixture of Cu/Zn-An ultrastructural study.

The hepatopancreas of crustaceans species has been recognized as an essential target organ to assess trace elements' effects. Due to its dynamic and capability of detoxifying trace metal, this organ often indicates distinct pathological disturbances. In the present work, we intend to evaluate the bioaccumulation of trace metal in three Orchestia species (Orchestia montagui, Orchestia gammarellus, and Orchestia mediterranea) living in symmetry in the banks of Bizerte lagoon (37°13'8″N 09°55'1″E) after their exposure during 14 days to a mixture of copper and zinc, and to highlight the effect of these metals on their hepatopancreas ultrastructure using transmission electron microscopy. At the end of the experiment, results showed that the mortality and the body mass varied according to the used nominal concentrations. Significant alterations were noted in all the treatment groups. The degree of these alterations depends on the used concentration, and they are represented especially by the cells remoteness and the border lyses, the reduction of the nuclear volume, the increase in the cytoplasm density with the presence of trace metal in the nucleus as well as in the vacuole, the disorganization and the destruction of microvilli, the condensation of the majority of cellular organelles and mitochondria swelling. Through this study, Orchestia genus could be an attractive candidate for the biochemical study of trace metal toxicity in Tunisian wetlands.

Distribution of organochlorine pesticides in sediment cores from the Bizerte Lagoon (Tunisia)

ABSTRACT The present study investigates the vertical distribution of organochlorine pesticides (OCPs), in two sediment cores collected from the Bizerte Lagoon. The sediment core (SC1) is located in the mouth of the channel connecting the lagoon to the Mediterranean Sea and characterized by the industrial and urban activities of zone A and B. The sediment core (SC2) is situated in the zone D known by its intensive metallurgy and naval construction activities. The OCPs concentrations ranged from 26.98 ± 0.04 ng g−1 found at 3 cm depth and 10.23 ± 0.02 ng g−1 at 6 cm depth in SC1, and varied between 11.77 ± 0.11 ng g−1 at 9 cm depth and 1.47 ± 0.02 ng g−1 at 20 cm depth in SC2. The results showed that the SC2 had lower levels of OCPs and total organic carbon (TOC) compared to SC1. Generally, OCPs and TOC % decreased with depth along the two SCs profiles. The different categories of OCPs were in the following order: DDTs> Aldrin >HCB. The principal OCPs in deeper sediment layers were aldrin, endrin, and ∑DDTs for SC1 in addition to HCB and aldrin for SC2. The predominant OCPs in surface sediments were dieldrin, endrin and ∑DDTs for SC1, and HCB, heptachlor, aldrin and ∑DDTs for SC2. Different profiles were observed making evident that the levels of these pollutants depend strongly on anthropological discharges from industrial, urban and farming sources. The temporal trends of OCPs were influenced by their different historical usages, different properties or different degradation conditions in the environment. DDTs was mainly due to historical residue and biodegradation occurred in aerobic conditions. According to the established guidelines for sediment quality, levels of OCPs at most of the SCs layers were below class criteria. However, levels of DDE in SC1 could cause biological damage and ecotoxicological risk.

Impact of heavy metals of industrial plant wastewater on benthic communities of Bizerte Lagoon (Tunisia)

ABSTRACTThe aim of this study was to assess the consequences of human impact on the characteristics of sediments heavy metal concentration, grain size and its influence on the structure of the microbial and meiofaunal community assemblages. A survey was carried out in July 2013 within six sites located in the Bizerte Lagoon (Tunisia), both downstream and upstream of industrial effluents. The highest total sediment metal concentrations were detected in stations located close to the industrial sewage discharge points. In these stations, the lowest densities of the total meiofauna (33 ± 13 ind/10 cm−2) and conversely the highest densities of cultivable bacteria that are heavy metal resistant have been reported (16 ± 80.34 CFU g−1). Univariate (ANOVA) and multivariate (MDS/CCA) analyses demonstrate high dissimilarity (0.06) in meiofaunal and bacterial community structures between downstream and upstream industrial sewages. Furthermore, canonical correspondence analysis CCA results indicated that heavy metal sediment contamination promoted bacteria that are resistant to heavy metals, while heterotrophic bacteria supported the development of meiofauna taxa. The results highlight the importance of bacteria/meiofauna interactions, as both meiofaunal and microbial communities give indications of the ecological impact of heavy metal contamination in sediment.

Bacterial community assemblages in sediments under high anthropogenic pressure at Ichkeul Lake/Bizerte Lagoon hydrological system, Tunisia

Bacterial communities inhabiting sediments in coastal areas endure the effect of strong anthropogenic pressure characterized by the presence of multiple contaminants. Understanding the effect of pollutants on the organization of bacterial communities is of paramount importance in order to unravel bacterial assemblages colonizing specific ecological niches. Here, chemical and molecular approaches were combined to investigate the bacterial communities inhabiting the sediments of the Ichkeul Lake/Bizerte Lagoon, a hydrological system under anthropogenic pressure. Although the microbial community of the Ichkeul Lake sediment was different to that of the Bizerte Lagoon, common bacterial genera were identified suggesting a lake-lagoon continuum probably due to the hydrology of the system exchanging waters according to the season. These genera represent bacterial "generalists" maintaining probably general biogeochemical functions. Linear discriminant analysis effect size (LEfSe) showed significant differential abundance distribution of bacterial genera according to the habitat, the pollution type and level. Further, correlation analyses identified specific bacterial genera which abundance was linked with pesticides concentrations in the lake, while in the lagoon the abundance of specific bacterial genera was found linked with the concentrations of PAHs (Polycyclic aromatic hydrocarbons) and organic forms of Sn. As well, bacterial genera which abundance was not correlated with the concentrations of pollutants were identified in both lake and lagoon. These findings represent valuable information, pointing out specific bacterial genera associated with pollutants, which represent assets for developing bacterial tools for the implementation, the management, and monitoring of bioremediation processes to mitigate the effect of pollutants in aquatic ecosystems.

Microplastics in commercial molluscs from the lagoon of Bizerte (Northern Tunisia)

Microplastic (MP) pollution was investigated, for the first time, in six commercial molluscs collected from the lagoon of Bizerte during March 2018. The objective of this study was to determine the bioavailability of MPs to marine organisms and their risk for consumers of seafood. MP concentrations varied from 703.95 ± 109.80 to 1482.82 ± 19.20 items kg−1 wet weight. Three types of coloured MPs, including fibres, fragments and films were recovered. Fibres were the most common MP type isolated in each species. The most common size class was 0.1–1 mm. The FTIR-ATR analysis confirmed the presence of two polymer types polyethylene and polypropylene. Our results suggest that MP pollution was widespread and exhibited a relatively high level in commercial molluscs collected from Bizerte lagoon, suggesting trophic transfer in the food web and human exposure risks by diet. More investigations on MPs should be conducted in seafood and other marine organisms.

Microplastics in freshwater environment: the first evaluation in sediments from seven water streams surrounding the lagoon of Bizerte (Northern Tunisia).

Microplastic (MP) concentrations were determined, for the first time, in surface sediment of seven streams around the lagoon of Bizerte (Northern Tunisia), using a saturated NaCl flotation technique. Microplastics were categorised according to type, colour and size using a stereoscopic microscope. Results showed that all sediment samples contained MPs. The greatest MP abundance was observed at Jedara stream (6920 ± 395.98 items kg-1 dry weight), while the lowest mean value was 2340 ± 227.15 items kg-1 dry weight at Khima stream. The highest numbers of MPs were from streams near populated areas and municipal and industrial effluent discharges. Samples were made up entirely of secondary MPs mainly fibres, followed by fragments and films. The predominant colours were as follows: black > clear > white > red > blue > green > yellow for fibres, white > blue > black > red for fragments and red > white > clear > green > blue = black for films. Microplastic particles in the samples ranged from 0.2 to 5mm in length. FTIR analysis revealed that the abundant polymers were polypropylene and polyethylene. This work contributes to the growing evidence that MP contamination is widespread even in freshwater ecosystems and provides a baseline for future studies and risk assessments.

Enhancement of mixture pollutant biodegradation efficiency using a bacterial consortium under static magnetic field.

One of the main challenges of bioremediation is to define efficient protocols with low environmental impact and high removal rates, such as static magnetic field (SMF). The aim of this study was to evaluate the effect of SMF exposure on the biodegradation rate of a mixture of pollutants using three bacterial strains which were isolated and identified from the Bizerte lagoon: Pseudomonas stutzeri LBR (KC157911), Cupriavidus metallidurans LBJ (KU659610) and Rhodococcus equi LBB (KU743870). To recognize the improvement role of SMF, the culture was submitted to a pre-treatment with SMF with an induction equal to 200 mT for 5 hours, after that the degradation experiment was followed with individual strains and with a consortium. Results showed an increase by 20% in the growth of the exposed bacterial population compared to controls, and 98% of biodegradation of DDT and 90% for BaP after 30 days of follow-up. This encouraging data opens new perspectives for a bioremediation bioprocess using SMF.

An assessment of copper, zinc and cadmium contamination and their ecotoxicological effects in O. mediterranea Costa, 1853 (Amphipoda, Talitridae)

ABSTRACTThis study was conducted to compare metals bioaccumulation in the Talitrid O. mediterranea collected from the banks of Bizerte lagoon. Individuals were exposed to a series of contaminated soil with different concentrations of cadmium, copper, and zinc. Biological and physiological responses were highlighted. Body metals concentrations were measured in the talitrid using flame atomic emission spectrometry. Results showed that after the second week, the mortality increased especially with cadmium exposure, and a mass gain was obtained between weeks for copper and zinc. Furthermore, the concentration factor indicated that O. mediterranea could be considered as a macroconcentrator of copper and zinc. Histopathological analysis showed that the different metals concentrations induced significant changes in the morphology and in the ultrastructural organisation of hepatopancreatic cells. Significant alterations obtained after metals exposure were the increase in the number of the majority cell organelles. Also, heavy metals were present in the form of numerous granules with different size in the cell surface. Furthermore, metals exposure affected the brush border causing the disruption of microvilli filament. Through these results, O. mediterranea could be a good indicator providing measurable responses. It could be an attractive candidate for the biochemical study of heavy metals toxicity in coastal ecosystems.

Occurrence of halogenated flame retardants in sediments and sea urchins (Paracentrotus lividus) from a North African Mediterranean coastal lagoon (Bizerte, Tunisia)

Classic (polybromodiphenyl ethers, PBDEs) and emerging halogenated flame retardants (HFRs) such as hexabromobenzenze (HBB), pentabromoetilbenzene (PBEB), decabromodiphenyl ethane (DBDPE) and halogenated norbornenes (HNs), as well as naturally produced methoxylated-PBDEs (MeO-PBDEs), were analyzed in 12 sediment and 30 urchin (Paracentrotus lividus) samples collected from Bizerte Lagoon in northern Tunisia. Levels of HFRs in the sediments ranged from nd to 51.8 ng/g dry weight (dw), while MeO-PBDEs were not detected. As regards levels in urchins, concentrations of PBDEs, HNs and MeO-PBDEs ranged from 3.67 to 56.9, 4.52 to 116 and nd to 364 ng/g lipid weight (lw), respectively. Thus, levels of naturally occurring compounds were higher than those of an anthropogenic origin. As regards HFRs, the highest contribution comes from HNs with levels ranging between 9.98 and 143 ng/g lw. HN and PBDE concentrations in sea urchin are similar or slightly lower than other reports for other species, while total MeO-PBDE concentrations are higher. The comsumption of sea urchins in Bizerte city is not a threat to public health concerning PBDE intakes.

Evaluating polar pesticide pollution with a combined approach: a survey of agricultural practices and POCIS passive samplers in a Tunisian lagoon watershed.

A study of pesticides in the Bizerte lagoon watershed on the Mediterranean coast of Tunisia showed that herbicides and fungicides are the most commonly used compounds. A survey was made of selected farmers. Pesticide contamination was monitored in the water column and sediments at four selected sampling sites (lagoon (A) and in three oueds-Chegui (B), Garaa (C), and Tinja (D)). Polar organic chemical integrative samplers (POCIS) were used to assess pesticide contamination. Thirty-two pesticides were investigated; the total concentration of active ingredients ranged from 35.9ngL-1 in Tinja oued to 1246ngL-1 in Chegui oued. In the lagoon, the total concentration of pesticides was 67.7ngL-1. In the sediments, the highest concentration was measured in Chegui oued in the spring (31ngg-1 dw). The main compounds found in the analyzed sediments were prosulfocarb and tebuconazole molecules.

Seasonal variation of the locomotor behavior of two sympatric species, Orchestia montagui and Orchestia gammarellus (Amphipoda, Talitridae), under aperiodic regimens

ABSTRACTLocomotor activity rhythms of Orchestia montagui and Orchestia gammarellus were investigated in populations collected from Bizerte lagoon banks. The locomotor rhythm of these two species was recorded in individual animals under continuous light and constant darkness over four seasons.Results revealed that the mortality was higher under continuous light than constant darkness. Whatever the season and species, a great variability of locomotor rhythm ranging from unimodal patterns to multimodal patterns via bimodal patterns was observed. In addition, double-plotted actograms obtained for the two species showed the presence of a clear drift to the right. This drift was more important under continuous light than constant darkness, lengthening thus the circadian period. Furthermore, the ultradian component was observed. Whatever the season, circadian rhythmicity was shorter under continuous light than constant darkness. Individuals of O. montagui were less active under continuous light than constant darkness whatever the season; whereas, those of O. gammarellus were more active under continuous light than constant darkness, especially in summer and autumn.The seasonal locomotor activity pattern variability of these sympatric species will be discussed as an adaptive strategy to cope with environmental conditions.

Nutritional value of the Tunisian mussel Mytilus galloprovincialis with a special emphasis on lipid quality

This study reports, for the first time, data on nutritional quality parameters in Tunisian mussels, Mytilus galloprovincialis, with an especial emphasis on lipid compounds. Mussel condition index (CI), proximate composition and fatty acid profiles were investigated for a one year period in order to identify the best harvesting period. Analysis revealed that polyunsaturated fatty acids (PUFA) were the dominant fatty acids with a prevalence of n-3 over n-6 forms. Pearson’s correlation indicated a strong relationship between CI and PUFA compound and Principal Components Analysis suggested that, from winter to summer, the product maintained a condition sufficiently good for marketing. The best CI and lipid quantity/quality occurred during summer and this may be used as criteria for product labelling. The study also included a thorough literature review that allowed data comparison on mussels from various Mediterranean sites and allowed the mussels from the Bizerte lagoon (North of Tunisia) to be differentiated.