Distribution of resting cysts of the potentially toxic dinoflagellate Alexandrium pseudogonyaulax in recently-deposited sediment within Bizerte Lagoon (Mediterranean coast, Tunisia)

This study investigated the spatial distribution of Alexandrium pseudogonyaulax resting cysts in recently deposited sediment of Bizerte lagoon (South-Western Mediterranean, Tunisia). This lagoon is the subject of many anthropogenic impacts, such as holding important fishing and aquaculture activities. A. pseudogonyaulax has been shown to produce Goniodomin A, which is a biologically-active compound. We showed that this dinoflagellate produces two types of resting cysts, which could be distinguished by the presence or the absence of a paratabulate wall. The average cyst density across the whole lagoon was rather high, reaching 639 cysts g1 of dry sediment (DS). Cyst densities varied widely among the sampled stations, with the highest density of 1685 cyst g1 DS being recorded at station 51 near a mussel farm. With respect to sediment characteristics, the highest cyst densities were found within silty sediments with high water content values. The distribution of A. pseudongoyaulax cysts in Bizerte lagoon appears to be related to hydrodynamic factors.peer-reviewe

Do the levels of industrial pollutants influence the distribution and abundance of dinoflagellate cysts in the recently-deposited sediment of a Mediterranean coastal ecosystem?

We studied the relationships between sediment industrial pollutants concentrations, sediment characteristics and the dinoflagellate cyst abundance within a coastal lagoon by investigating a total of 55 sampling stations within the Bizerte lagoon, a highly anthropized Mediterranean ecosystem. The sediment of Bizerte lagoon is char- acterized by a high dinocyst abundance, reaching a maximum value of 2742 cysts·g−1 of dry sediment. The investigated cyst diversity was characterized by the presence of 22 dominant dinocyst morphotypes belonging to 11 genera. Two dinoflagellate species dominated the assemblage: Alexandrium pseudogonyaulax and Protoperidinium claudicans, representing 29 to 89% and 5 to 38% of the total cyst abundance, respectively, depending on the station. Seven morphotypes belonging to potentially toxic species were detected, including Alexandrium minutum, A. pseudogonyaulax, Alexandrium catenella/tamarense species complex, Lingulodinium polyedrum, Gonyaulax cf. spinifera complex, Prorocentrum micans and Protoceratium reticulatum. Pearson correlation values showed a positive correlation (α = 0.05) between cyst abundance and both water content and fine silt sediment content. Clustering revealed that the highest abundance of cysts corresponds to stations presenting the higher amounts of heavy metals. The simultaneous autoregressive model (SAM) highlighted a significant correlation (α = 0.05) between cyst accumulation and two main factors: sediment water content and sediment content for several heavy metals, including Hg, Cd, Cu, Ni and Cr. These results suggest that the degree of heavy metal pollution could influence cyst accumulation patterns.peer-reviewe

Distribution et écologie des Méduses (Cnidaria) du golfe de Tunis (Méditerranée sud occidentale)

The Medusae of Tunis Gulf (25 species) are qualitatively the third zooplanktonic group after Tintinnids and Copepods. Anthomedusae (eight species), Trachymedusae (five species) and Leptomedusae (four species) represent the major part among the 20 species of Hydromedusae identified during our study (December 1993-November 1995). However, the Limnomedusae (two species) and the Narcomedusae (one species) are poorly represented. In the Bay of Tunis, Obelia spp., the most common and dominant species, command the quantitative fluctuations of Hydromedusae and reach exceptionally the density of 25 800 ind. m(-3). Within the Scyphomedusae (five species), Pelagia noctiluca is the most common species which outbreaks in winter and autumn. Tunis Gulf seems to be, composed of two jellyfish communities; the first one is composed of endogenous species showing a constant period of blooming like Olindias, Cladonema, Aurelia, Cotylorhiza and Rhizostoma and sometimes permanent like Obelia spp. and Clytia spp.; the second. is represented by exogenous species considered as "visitors" like Velella, Sminthea or Pelagia whose presence on the coast is dependent on local and particular winds and currents.Les méduses du golfe de Tunis représentées par 25 espèces constituent du point de vue taxonomique le troisième groupe zooplanctonique après les Tintinnides et les Copépodes. Parmi les 20 Hydroméduses recensées au cours du cycle d’étude (décembre 1993–novembre 1995), les anthoméduses (huit espèces), les trachyméduses (cinq espèces) et les leptoméduses (quatre espèces) sont les plus diversifiées. Les Limnoméduses (deux espèces) et les Narcoméduses (une espèce) étant les sous-classes les moins représentées. Ce sont les espèces du genre Obelia et Clytia qui commandent la dynamique quantitative des hydroméduses dans la baie avec des poussées susceptibles d’atteindre des valeurs exceptionnelles de l’ordre de 25 800 ind/m3 pour Obelia spp. Au sein des scyphoméduses dont la richesse spécifique s’élève à cinq espèces, Pelagia noctiluca est l’espèce la plus commune, dont les invasions s’observent en saison automnale et surtout hivernale. Le golfe de Tunis apparaît comme formé par deux types de communautés de Méduses ; la première endogène constituée d’espèces constantes dans leur apparition tel que Olindias, Cladonema, Aurelia, Cotylorhiza et Rhizostoma et parfois pérennes comme Obelia spp., Clytia spp. ; la deuxième exogène à répartition spatiotemporelle irrégulière et représentée par des espèces visiteuses comme Velella, Sminthea ou encore Pelagia dont la présence sur la côte résulte de la présence de vents et de courants locaux particuliers

Spatio-temporal distribution of the dominant Diatom and Dinoflagellate species in the Bay of Tunis (SW Mediterranean Sea)

Microphytoplankton composition and its relationships with hydrology and nutrient distributions were investigated over 24 months (December 1993 - November 1995) in the Bay of Tunis ( SW Mediterranean Sea). A new index, the ‘Specific Preference Index’ (SPI) obtained by computing the median value of each parameter weighed by the numerical value of each species density was developed. Using this index, the relationships between each species and temperature, salinity and major nutrients were analysed. The distribution of chlorophyll a did not show a clear correlation with microplankton abundance suggesting that other factors contribute to chlorophyll concentration, such as smaller phytoplankton size fractions or detritus. The winter-spring diatom blooms did not show a regular pattern during both years. High nutrient inputs in late summer, associated with mild meteorological conditions, contributed to the development of a large diatom bloom in autumn 1995 where significant silicate depletion was witnessed. Generally, diatoms were more stenotherm than dinoflagellates in the Bay, whereas dinoflagellates were more stenohaline than diatoms. The statistical analyses showed that the two species, Bellerochea horologicalis , and Lithodesmioides polymorpha, var., tunisiense, appeared in a wide range of environmental conditions. An excess of phosphateversus nitrate appeared to be associated with red tides of, Gymnodinium spp, whereas Peridinium quinquecorne, showed the opposite. Phosphate concentrations appear to be crucial in this coastal environment, where diatom blooms are often limited by low silicate availability

Environmental controlling factors of copepod communities in the Gulf of Tunis (south western Mediterranean Sea)

The copepod community structure and the distribution of the main groups of zooplankton were studied along an inshore-offshore gradient in the Gulf of Tunis during the rainy and dry seasons of 2007-2008. Hydrological parameters were also measured to assess the potential role of abiotic and biotic factors in the distribution of copepod species. The copepod community in the Gulf of Tunis comprises 86 species dominated by Paracalanus parvus, Clausocalanus lividus, Centropages kroyeri and Acartia clausi. Time had a greater influence than space (horizontal and vertical gradients) in shaping the copepod community structure with a significant influence of the seasons; winter (cold and rainy) resulted in hydrological conditions that were strongly different from those observed in summer (warm and dry). These hydrological differences were concomitant with changes in the community structure, with a high copepod diversity observed in winter while the summer period was characterized by a low specific richness and the dominance of a few species, Centropages kroyeri and Paracalanus parvus along the inshore-offshore gradient and Paracalanus aculeatus along the vertical. Canonical correspondence analysis showed that temperature, salinity and to a lesser extent chlorophyll a were the most important environmental factors structuring the copepod community. Interestingly, temperature and salinity showed a negative significant correlation with copepod specific richness. Competition with grazers (cladoceran) as well as top down control by predators (chaetognaths and siphonophors) were also identified as key factors for the copepod community structure

Seasonal variability of picophytoplankton under contrasting environments in northern Tunisian coasts, southwestern Mediterranean Sea

Highlights: • Picophytoplankton was able to grow under a wide range of environmental conditions varying seasonally. • Picophytoplankton variability was more marked in the bay than in the lagoon. • Picophytoplankton decreased in the lagoon under enhanced anthropogenic stress. • Synechococcus, the most abundant group of the community, was frequently present in both ecosystems during the monitoring. We investigated at the single cell level during 16months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225*103 cells·cm-3 in the Bay and 278*103 cells·cm-3 in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems

First report of goniodomin A production by the dinoflagellate Alexandrium pseudogonyaulax developing in southern Mediterranean (Bizerte Lagoon, Tunisia)

The dinoflagellate Alexandrium pseudogonyaulax is widely distributed around the world including the Mediterranean waters. The objectives of this study were to determine the morphology and phylogenic affiliation of A. pseudogonyaulax strain isolated from Bizerte Lagoon (Mediterranean waters, Tunisia) and investigate its toxicity. Molecular analyses confirmed the morphological identification of the isolated strain (APBZ12) as A. pseudogonyaulax. Moreover, it showed that it is 100% identical with strains of this species found in New Zealand, Japan, China and North Sea (Norway and Denmark) suggesting that this species is cosmopolitan. Until now, no toxin studies have been conducted on fully characterized (morphologically and molecularly) A. pseudogonyaulax. Cellular toxin production was determined using high pressure liquid chromatography coupled to mass spectrometry (HPLC/MS). Results showed for the first time that A. pseudogonyaulax contains goniodomin A (GDA), a highly toxic macrolide polyether previously shown to be produced by two other dinoflagellate species Alexandrium monilatum (Hsia et al., 2006) and Alexandrium hiranoi (erroneously identified as A. pseudogonyaulax in Murakami et al., 1988) in American and Japanese waters, respectively. This biologically active toxin has been associated over decades with fish mortality. Our study showed that the cell extracts of APBZ12 showed an important bioactivity using GH4C1 rat pituitary cytotoxicity bioassay

Consequences of a contaminant mixture of bisphenol A (BPA) and di-(2-ethylhexyl) phthalate (DEHP), two plastic-derived chemicals, on the diversity of coastal phytoplankton

To assess the impact of two plastic derived chemicals: bisphenol A (BPA) and the di-2-ethylhexyl phthalate (DEHP), on phytoplankton biomass and community structure, microcosm incubations were performed during spring and summer, with offshore and lagoon waters of a south-western Mediterranean ecosystem. Phytoplankton were exposed to an artificial mixture of BPA and DEHP and to marine water previously enriched with plastic-derivative compounds, originated from in situ water incubations of plastic debris for 30 days. After 96 h of incubation, changes were observed in phytoplankton biomass in the contaminated microcosms, with a net decrease (up to 50% of the control) in the concentration of Chlorophyll a in offshore waters. Concomitantly, plastic-derivative contamination provoked structural changes, especially for offshore waters. This suggests a relative tolerance of the lagoon communities to BPA and DEHP contamination, related to the dominance of Chaetoceros spp., which could potentially be used as a bioindicator in bioassessment studies

Impact of two plastic-derived chemicals, the Bisphenol A and the di-2-ethylhexyl phthalate, exposure on the marine toxic dinoflagellate Alexandrium pacificum

International audienceThe effects of two plastic-derived chemicals: Bisphenol A (BPA) and di-2-ethylhexyl phthalate (DEHP) were assessed on abundance and physiological responses of the marine toxic dinoflagellate Alexandrim pacificum. During 7 days experiment, A. pacificum was exposed to different levels of BPA and DEHP (separately and in mixture). The responses were evaluated and compared with controls. Results showed that A. pacificum was highly sensitive to this contaminants comparing to other phytoplankton species. BPA and DEHP caused the decrease of the biomass (1.2 to 50 times lower relative to the controls), as well as the perturbation of the photosystem and the photosynthetic activity. Nevertheless, our results show a recovery of contaminated cells activity depending on exposure time and BPA and DEHP contamination. This could be related to an adaptation to induced stress or a degradation of BPA and DEHP in the medium

Jellyfish blooms perception in Mediterranean finfish aquaculture

In recent years, negative impacts of jellyfish blooms (JB) on marine human activities have been increasingly reported. Aquaculture has been affected by jellyfish outbreaks, mostly documented through repeated episodes of farmed salmon mortalities in Northern Europe; however, the valuation of JB consequences on the aquaculture sector still remains poorly quantified. This study aims to provide the first quantitative evaluation effects of JB on finfish aquaculture in the Mediterranean Sea and to investigate the general awareness of JB impacts among Mediterranean aquaculture professional workers. The aquaculture workers' perception about JB was assessed through a structured interview-based survey administered across 21 aquaculture facilities in central and western Mediterranean. The workers' awareness about JB impacts on aquaculture differed among countries. Italian and Spanish fish farmers were better informed about jellyfish proliferations and, together with Tunisian farmers, they all recognized the wide potential consequences of JB on sea bream and sea bass aquaculture. On the contrary, the majority of Maltese respondents considered JB as a non-significant threat to their activity, mostly based on off-shore tuna farming. This study for the first time shows that JB may negatively affect different Mediterranean aquaculture facilities from Tunisia (Sicily Channel) and Spain (Alboran Sea), by increasing farmed fish gill disorders and mortality, clogging net cages, or inflicting painful stings to field operators, with severe economic consequences. Available knowledge calls for the development of coordinated preventive plans, adaptation policies, and mitigation countermeasures across European countries in order to address the JB phenomenon and its impacts on coastal water activities