Driving factors of the potentially toxic and harmful species of Prorocentrum Ehrenberg in a semi-enclosed Mediterranean lagoon (Tunisia, SW Mediterranean)

We analysed the dynamics of the potentially toxic and harmful species of Prorocentrum Ehrenberg in Bizerte lagoon (important aquaculture area, Northern Tunisia), substantiating the possible driving forces (temperature, salinity and nutrients), based on a two years database. We revealed that Prorocentrum spp. blooms of high magnitude (104 - 105 cells l-1) occurred mostly during the period of late winter to early spring. We found five species of Prorocentrum, two of which, P. lima and P. cordatum, the most common during the field, are confirmed agents of Diarrhetic Shellfish Poisoning in various regions of the world ocean. Prorocentrum sp., P. micans, and P. gracile were however present only sporadically but with high cell abundances, exemplifying bloom densities. Canonical correspondence analysis revealed that P. minimum and P. lima were much more abundant in eutrophied waters characterized here by high Chl a biomass, while P. gracile species occurred principally in warm waters. Furthermore, Prorocentrum sp. and P. micans seemed more likely to proliferate in saline waters with high concentrations of inorganic nutrients (nitrate, ammonia and phosphate). Our study calls attention to a possible intensification of DSP events in the Bizerte lagoon, given the propensity of Prorocentrum spp. to proliferate in a eutrophied system

Factors driving the seasonal dynamics of Pseudo-nitzschia species and domoic acid at mussel farming in the SW Mediterranean Sea

The seasonal variations in Pseudo-nitzschia species and domoic acid (DA) concentration were investigated, at three shellfish farms in SW coastal Mediterranean. In parallel, the toxicity of mussels was tested. Two distinct groups of species were enumerated according to morphology and size (Pseudo-nizschia delicatissima and P. seriata groups). DA was detected over a nine-week period from July to October 2012 in the Lagoon, with a maximum concentration recorded in July (12.71 ng DA L−1). DA was positively correlated with the presence of P. seriata-group and P. delicatissima-group and was mostly occurred during P limitation period in seawater. No DA was found in mussels that were collected during the period of DA absence in seawater. Our results suggest that temperature, salinity, inorganic and organic nutrients were significant for the seasonal dynamics of P. seriata and P. delicatissima groups, but that the P limitation was the most driving factor for DA production in these areas. The relative influence of environmental factors should be further studied to better understand the recent surfacing of massive blooms of toxigenic Pseudo-nitzschia in SW Mediterranean coast.info:eu-repo/semantics/acceptedVersio

Effects of polycyclic aromatic hydrocarbons on marine and freshwater microalgae – A review

International audienc

Structural and functional responses of coastal marine phytoplankton communities to PAH mixtures

The toxicity of polycyclic aromatic hydrocarbons (PAHs) mixtures was evaluated on natural phytoplankton communities sampled from lagoons of Bizerte (South-western Mediterranean Sea) and Thau (North-western Mediterranean Sea). PAHs induced short-term dose and ecosystem-dependant decreases in photosynthetic potential. Chlorophyll a was negatively affected by increasing PAHs concentrations, together with dramatic changes in phytoplankton community composition. Size classes were strongly affected in the Bizerte compare to the Thau lagoon, with a decrease in nano- and microphytoplankton densities compare to picophytoplankton. In both locations, the diatom Entomoneis paludosa appeared favoured under PAH exposure as evidenced by increase in cell density, whereas autotrophic flagellates and dinophytes were strongly reduced. Smaller cells were more tolerant to exposure to highest PAHs concentrations, with persistent picophytoplankton carbon biomass at the end of the incubations. Apparent recovery of photosynthetic potential, accompanied with a regrowth of chlorophyll a under the lowest PAH doses, coincided with a significantly altered community composition in both lagoons. Furthermore, sensitivity to PAHs was not related to the phytoplankton cell size, and toxicity-induced modification of top-down control by grazers during the experiment cannot be excluded

Impact of contaminated sediment elutriate on coastal phytoplankton community (Thau lagoon, Mediterranean Sea, France)

Effects of sediment-released contaminants and nitrogen were assessed on phytoplankton communities sampled from Thau lagoon (France, Mediterranean Sea) and one close offshore marine station. Phytoplankton was exposed to sediment elutriate (seawater containing a mix of metals, organic chemicals, and nutrients) or to ammonium enrichment for four days using immersed microcosms exposed to natural conditions of light and temperature. Functional (production - respiration balance) and structural (taxonomy and cell densities) responses of the phytoplankton community were assessed. In the lagoon, both treatments stimulated phytoplankton growth, compare to controls. Conversely in the offshore station, the phytoplankton growth was stimulated only with the sediment elutriate addition. In offshore and lagoon stations, both treatments caused a shift in the taxonomic composition of the phytoplankton. Proliferation of potentially toxic diatoms and dinoflagellates resulted from the addition of elutriate. Correspondence analysis determined that phytoplankton from the offshore station was more sensitive to both treatments compared to the lagoon community. According to daily production and respiration balance, lagoon community metabolism remained heterotrophic (P R) were observed in the offshore community. Direct toxicity of contaminants released from sediment, if any, was therefore masked by nutrient enrichment effects, whereas indirect evidence of contaminant pressure was highlighted by changes in community composition and metabolism

POLLUTION AND SEA WATER IN THALASSOTHERAPY CENTERS OF TUNISIA (SW MEDITERRANEAN COASTAL)?

The practice of thalassotherapy in Tunisia has been possible while applying statement of Decree 92-129 published July 13, 1992 setting standards and conditions for implementation and exploitation of thalassotherapy centers (TCs), modified and replaced by Decree 2001-1081 of May 14, 2001 and Decree 2006-3174 published November 30, 2006 according to Tunisian standard 126.05 (2007). Recently, this Tunisian standard was origin of the international standard ISO 17680. Concerning quality of seawater used by TCs, these standards require the assay: trace metals (cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), selenium (Se) and chromium (Cr)), total hydrocarbons (THC), polycyclic aromatic hydrocarbons (PAHs), surface active substances to the methylene blue. The legislation (ISO 17680) cited limits concentration not exceeded. Concerning sewage sea water, Decree 3174-2006 of 30 November 2006 requires that seawater discharged into the marine environment, complies with the Tunisian standard NT 106 002 on liquid discharges in the receiving environment. In part, through the application of these standards, Tunisia was, after France, second destination for thalassotherapy. Thus, to maintain this privileged position and even more advanced in this field, the National Office of Thermalism and Hydrotherapy (NOTH) applied standards ISO 17680 and monitored pollutants concentrations of sea water, which is the main tool for working thalassotherapy centers (TCs). Hence, this study is the first, nationally and internationally, assessing the impact of anionic detergents, heavy metals (cadmium (Cd, Pb, As, Hg, Se and Cr), total hydrocarbons (THC) and detergents (anionic substances) on seawater quality used by six TCs situated in four coastal regions from north to south (Hammamet, Sousse, Monastir and Mehdia) during four months (from May to September 2014). The pollutants concentrations monitored varying among TCs and months. Indeed, Cd concentrations ranged from 1 to 5.10-3 mg.l-1, Pb from 1 to 5.10-2 mg.l-1, Cr from 1 to 17.10-2 mg.l-1 and Hg from 0.2.10-3 to 71.10-2 mg.l-1. Arsenic, Se and anionic detergents concentrations were reached 2, 4 and 10.10-2 mg.l-1, respectively in different TCs. Concentrations of total hydrocarbons were below 0.1 mg.l-1 in the majority of TCs and finally anionic detergents measured in sewages TCs reached respectively 5.08 and 0.3mg.l-1 in sewages TCs B and C. The factorial correspondence analysis (FCA) showed 3 distinct groups: The FCA has shown that concentrations of the highest total hydrocarbons were registered in TCs A, B, E and F. The second group is represented by center C which is characterized by the highest Hg concentrations and the third group represented mainly by single CT D. The latter group was characterized by the highest concentrations of Cr and Pb and the least concentration of Cd. Except anion detergents in sea water, the other pollutants (Cd, Pb, Cr, Hg and THC) exceeded concentrations recorded in the Mediterranean. The presence of these pollutants in the marine environment is due to wastes industrial, agricultural, to geochemical structure and mining) and directly by rivers, and precipitations or atmospheric deposits. Thus, we must be vigilant on these pollutants concentrations and their origins. Besides, the NOTH has taken the necessary measures for items that have exceeded the limits set by the standards concentrations, such as Hg and anionic detergents in sewage TCs. Indeed, except the latter two pollutants, Cd, Pb, Cr, As, anionic detergents and THC have not exceeded the limits set by the standard concentrations