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Genovesi, B., Mouillot, D., Laugier, T., Fiandrino, A., Laabir, M., Vaquer, A., et al. (2013). Influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella/tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms. Harmful Algae, 25, 15–25.
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Laanaia, N., Vaquer, A., Fiandrino, A., Genovesi, B., Pastoureaud, A., Cecchi, P., Collos, Y. (2013). Wind and temperature controls on Alexandrium blooms (2000-2007) in Thau Lagoon (Western Mediterranean). Harmful Algae, 28, 31–36.
Résumé: Since 1998, blooms of Alexandrium catenella/tamarense in the lagoon of Thau developed regularly each autumn, reaching a maximum of several millions cells per liter in 2004. By contrast, spring blooms occurred only twice (in 2000 and 2007). During these periods, sea surface temperatures (SST) and the wind patterns appear to impact the bloom occurrences much more than the apparent limiting resources such as inorganic nutrients. The analysis of SST and wind from April to June and September to November (from 2000 to 2007) indicates first that there has to be an initial wind stress in order to resuspend the cysts buried in the sediment. Blooms then occur after a period of weak winds (<4 m s(-1)) and of stable SST close to 20 degrees C (+/- 2 degrees C). Those conditions appear to be most favorable for germination of Alexandrium cysts and its ensuing vegetative growth. This period of stability (a few days to a few weeks) allows the development of the inoculum from the cyst's germination, its cohesion because of reduced hydrodynamics, and development of vegetative cells that are sensitive to agitation. Strong winds during 1-2 day periods can interrupt the bloom dynamics by dispersing (advection due to southeasterly winds) and/or eliminating (turbulence due to northwesterly winds) the vegetative cells. In the spring, under the same conditions of optimal SST, strong wind episodes dominate and those, as well as biological factors very likely lead to a lower occurrence of blooms relative to the fall situation. (C) 2013 Elsevier B.V. All rights reserved.
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Triki, H. Z., Daly-Yahia, O. K., Malouche, D., Komiha, Y., Deidun, A., Brahim, M., et al. (2014). Distribution of resting cysts of the potentially toxic dinoflagellate Alexandrium pseudogonyaulax in recently-deposited sediment within Bizerte Lagoon (Mediterranean coast, Tunisia). Marine Pollution Bulletin, 84(1-2), 172–181.
Résumé: 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 g(-1) of dry sediment (DS). Cyst densities varied widely among the sampled stations, with the highest density of 1685 cyst g(-1) 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. (C) 2014 Elsevier Ltd. All rights reserved.
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Triki, H. Z., Laabir, M., & Kéfi Daly-Yahia, O. (2015). Life history, excystment features, and growth characteristics of the Mediterranean harmful dinoflagellate Alexandrium pseudogonyaulax. J. Phycol., 51(5), 980–989.
Résumé: Studies considering the biology and ecology of the toxic bloom-forming species, Alexandrium pseudogonyaulax, are rare. Our results highlight five features not described before in A. pseudogonyaulax life cycle: (i) A. pseudogonyaulax gametes showed two modes of conjugation, anisogamy and isogamy, (ii) sexual conjugation occurs either in the dark or in the light phase by engulfment or a fusion process, (iii) the presence of planozygote and newly formed cysts in monoclonal culture suggests homothallism, (iv) newly formed cysts have very dark vesicular content and are mostly unparatabulated when observed under light microscope and (v) natural resting cysts are able to give either a planomeiocyte or two vegetative cells. Cyst viability was enhanced after 5 months of cold storage (4°C), with excystment rate reaching 97% after 3 d of incubation. Excystment rate was highest (43%–79%) in Enriched Natural Sea Water diluted culture medium, whereas few germling cells were able to survive without the culture medium (0%–13%). Salinity-irradiance experiments revealed that the highest cell concentrations occur at high irradiances for all the tested salinities. Vegetative growth rates generally increased with increasing irradiance, and were less dependent on salinity variations. The relatively low growth rate, low cell densities in the laboratory, and the notable capacity of producing cysts along growth phases of A. pseudogonyaulax could explain the occurrence of high resting cysts densities in the sediment of Bizerte lagoon and the relatively low abundances of vegetative cells in the water column.
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Triki, H. Z., Laabir, M., Lafabrie, C., Malouche, D., Bancon-Montigny, C., Gonzalez, C., et al. (2017). Do the levels of industrial pollutants influence the distribution and abundance of dinoflagellate cysts in the recently-deposited sediment of a Mediterranean coastal ecosystem? Sci. Total Environ., 595, 380–392.
Résumé: 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 characterized 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 (alpha = 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 (alpha = 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. (C) 2017 Elsevier B.V. All rights reserved.
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