12 pagesInternational audienceWe studied the summer spatial distribution of the copepod community in both the neritic and oceanic areas of the Gulf of Gabe`s (Tunisia, eastern Mediterranean Sea) coupled with environmental factors. Copepods were the most abundant zooplankton throughout the sampling period, contributing 78% of the total zooplankton. A total of 14 copepod families were identified in all stations, with an overwhelming abundance of Acartiidae and Oithonidae (39.05 and 39.09% of total abundance, respectively). Abundance of Acartia clausi and chlorophyll-a concentrations were negatively correlated with salinity, suggesting that this species probably escaped the high coastal salinity (38 psu). Significant correlation determined between A. clausi and tintinnids at 50 m isobaths indicates that these planktonic ciliates probably served as a substantial food link towards higher trophic levels of this area. Conversely, Oithona nana which was well adapted to high chlorophyll-a concentrations and high salinity along the coast, showed significant correlations with Dictyochophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae, suggesting that this small copepod was capable of feeding on a wide selection of phytoplankton preys

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21Cigarette butts are the most common plastic form of litter found in the marine coast, threatening 22 the quality of the seawater and marine life. However, the impact of cigarette butts known to 23 contain toxic chemicals has been investigated to date in very few marine species. This study 24 aimed to evaluate the effects of cigarette filters (smoked or unsmoked) on the microbial 25 diversity inhabiting coastal sediments by high-throughput sequencing of the 16S rRNA genes. 26Both bacterial structure and metals distribution were impacted by cigarette filter addition in 27 laboratory sediment experiments, compared to control sediment incubations without filter. Both 28 smoked and unsmoked cigarette filters decreased pH and dissolved Cd, Mo and V 29 concentrations in marine sediment incubations, while they increased dissolved Fe, Mn, Zn 30 levels in the surrounding environment. Smoked filters dramatically decreased the relative 31 abundance of the phyla Bacteroidetes and Cyanobacteria, while the members of the phyla 32 Gammaproteobacteria, Firmicutes and Thermotogae were enriched by smoked filters in marine 33 sediments. Bacterial taxa associated with deep marine environments or hydrothermal seep fields 34 were selected by smoked cigarette filters. This study demonstrated for the first time the 35 microbial community changes and impacts from toxic cigarette filters in coastal marine 36 sediments.

1 université de sfax, faculté des sciences de sfax, Département des sciences de la Vie, unité de recherche 00/ur/0907 ecobiologie, Planctonologie and microbiologie des ecosystèmes marins, route soukra km 3,5 BP 802 CP 3018 sfax, tunisie. 2 institut national des sciences et technologie de la mer, Centre de sfax BP 1035 sfax 3018 tunisie.3 institut national des sciences et technologie de la mer, 2025 salammbô tunis, tunisie. 4 université de franche-Comté, laboratoire de Chrono environnement, usC inra, umr Cnrs 6249, 1, Place leclerc, f-25030 Besançon cedex, france. SUMMARY:The summer spatial distribution of the dinoflagellate community along an open coastal sea gradient in the Gulf of Gabes (tunisia, eastern mediterranean sea), together with environmental factors, were studied. the most dominant families were represented by Gymnodiniaceae (32%), Peridiniaceae (20%), Prorocentraceae (15%), Ceratiaceae (13%) and Ebriaceae (10%). The dinoflagellate community was spatially more concentrated along the coast of the gulf than in the open sea. Eight toxic dinoflagellates were recorded, including Karenia cf. selliformis (37% of total toxic dinoflagellates) which was evenly distributed in both the neritic and open sea areas. Dinocysts contributed 33% of the total motile cells and were more abundant along the coast than in the open sea. this high concentration may be ascribed to nitrogen inputs in the coastal waters of Gabes. The Modified Atlantic Water governed dinoflagellate development in the open sea. The degradation of the water quality due to eutrophication in the Gulf of Gabes may have significant socioeconomic consequences. We suggest that a management framework, similar to that used in freshwater ecosystems, should be developed for the Gulf coast in order to drastically reduce urban interferences.Keywords: Gulf of Gabes, dinoflagellates, dinocysts, nutrients.resumen: Dinámica estival De DinoflagelaDos asociaDa con factores ambientales en el golfo De bages (túnez, meDiterráneo oriental). -Se estudió la distribución espacial de la comunidad de dinoflagelados junto con los factores ambientales a lo largo de un gradiente desde la costa a mar abierto en el Golfo de Gabes (túnez, mediterráneo oriental). las familias dominantes de dinoflagelados estuvieron representadas por Gymnodiniaceae (32%), Peridiniaceae (20%), Prorocentraceae (15%), Ceratiaceae (13%), and Ebriaceae (10%). La comunidad de dinoflagelados estuvo más concentrada a lo largo de la costa del Golfo que en mar abierto. Se detectaron 8 especies de dinoflagelados tóxicos entre los cuales, Karenia cf. selliformis (37% del total de dinoflagelados tóxicos) estuvo homogeneamente distribuida en la zona nerítica y en áreas de mar abierto. Dinocysts contribuyeron en un 33% del total de células móviles y fueron más abundantes a lo largo de la costa que en el mar abierto. esta alta concentración puede adscribirse a los vertidos de nitrógeno dentro de las agues costeras de Gabes. Las corrientes Atlánticas gobiernan el desarrollo de los dinoflagelados en el mar abierto. L...

(1) Background: Harmful algal blooms (HABs) can negatively impact marine ecosystems, but few studies have evaluated the microbial diversity associated with HABs and its potential role in the fates of these proliferations. (2) Methods: Marine prokaryotic diversity was investigated using high-throughput sequencing of the 16S rRNA gene during the bloom declines of two dinoflagellates detected in the summer of 2019 along the northern and southern Tunisian coasts (South Mediterranean Sea). The species Gymnodinium impudicum (Carthage, Tunis Gulf) and Alexandrium minutum (Sfax, Gabes Gulf) were identified using microscopy and molecular methods and were related to physicochemical factors and prokaryotic compositions. (3) Results: The abundance of G. impudicum decreased over time with decreasing phosphate concentrations. During the G. impudicum bloom decay, prokaryotes were predominated by the archaeal MGII group (Thalassarchaeaceae), Pelagibacterales (SAR11), Rhodobacterales, and Flavobacteriales. At Sfax, the abundance of A. minutum declined with decreasing phosphate concentrations and increasing pH. At the A. minutum peak, prokaryotic communities were largely dominated by anoxygenic phototrophic sulfur-oxidizing Chromatiaceae (Gammaproteobacteria) before decreasing at the end of the survey. Both the ubiquitous archaeal MGII group and Pelagibacterales were found in low proportions during the A. minutum decay. Contrary to the photosynthetic Cyanobacteria, the photo-autotrophic and -heterotrophic Rhodobacterales and Flavobacteriales contents remained stable during the dinoflagellate bloom decays. (4) Conclusions: These results indicated changes in prokaryotic community diversity during dinoflagellate bloom decays, suggesting different bacterial adaptations to environmental conditions, with stable core populations that were potentially able to degrade HABs.