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Zina A.,Institute National Des Science Et Technologies Of La Mer | Elbahri T.,Universite Ibn Tofail | Souad T.,Institute National Des Science Et Technologies Of La Mer | Naceur B.M.,Laboratoire Des Analyses Of Leau Of Mer | Ezzeddine M.,University of Carthage
Oceanological and Hydrobiological Studies | Year: 2012

The population dynamics of harmful microalgae was investigated in the semi-enclosed shallow lagoon, Tunis northern lagoon (South Mediterranean), during a 1-year period from January to December 2007. A total number of 16 potentially toxic dinoflagellates were identified. Density of each species was analyzed in time and space and in relation to environmental parameters. Some species such as Alexandrium catenella, A. pseudogonyaulax, A. tamarense, Dinophysis sacculus, Prorocentrum lima, P. minimum and Gonyaulax spinifera developed high cell concentrations, particularly during spring and summer seasons. Other species such as A. insuetum, A. lee, A. minutum, Coolia monotis, D. acuminata, D. caudata, D. fortii, Ostreopsis siamensis and P. concavum were detected in this coastal ecosystem, but they were rare or appeared in very low densities. Densities of the most abundant species were closely associated with spring and summer conditions, being positively correlated with water temperature and salinity. These species performed well in this lagoon, but the specific species-dependent affinity to each of the environment factors determined which organisms proliferated. The spatial distribution of the abundant species exhibited a marked increase towards the western and southern parts of the lagoon represented by sites C, D and E. Examination of the temporal distribution revealed that the species more prone to bloom are those with extensive spatial distribution and frequent presence throughout the year such as D. sacculus. Statistical analysis of D. sacculus density dynamics showed a significant difference between summer and winter assemblages. It presented a positive correlation with water temperature and salinity, but it seems to be tolerant to all levels of nutrients. Copyright © of Institute of Oceanography, University of Gdansk, Poland. Source


Armi Z.,Institute National Des Science Et Technologies Of La Mer Instm | Trabelsi E.,Laboratoire Des Analyses Of Leau Of Mer | Turki S.,Institute National Des Science Et Technologies Of La Mer Instm | Bejaoui B.,Institute National Des Science Et Technologies Of La Mer Instm | Maiz N.B.,Laboratoire Des Analyses Of Leau Of Mer
Journal of Marine Science and Technology | Year: 2010

Phytoplankton community structure was investigated in a 1-year study period from January to December 2006 in the Tunis North Lagoon (South Mediterranean). Twice a month, sampling was carried out from the whole water column. Phytoplankton species composition showed seasonal dynamics following the general environmental variable trends in the study area, with variation in species abundance levels within each season characterised by the presence of different phytoplankton communities. Analysis of environmental variables indicated that phytoplankton-dominant communities were associated with various water physicochemical characteristics, especially water temperature and salinity. Accordingly, significant correlation was recorded between water temperature and dinoflagellates (r = 0.35; p<0.05) in summer and diatoms (r = 0.69; p<0.05) in autumn, whereas euglenophytes, cyanophytes and chlorophytes were slightly correlated with temperature in autumn. Salinity was positively correlated with dichtyophytes (r = 0.41; p<0.05) in winter and with diatoms (r = 0.65; p<0.05) and euglenophytes (r = 0.57; p<0.05) in autumn. On the other hand, relationships between high nitrogen nutrient concentration and phytoplankton concentration were recorded for diatoms (r = 0.43; p<0.05 with NO 2; r = 0.49; p<0.05 with NO 3) in winter. Silicate concentration supported proliferation of diatoms (r = 0.58; p<0.05) in autumn in our study period. In contrast, increase of dinoflagellate concentration was associated with the decrease of these parameters in spring and summer. © JASNAOE 2010. Source


Armi Z.,Institute National Des Science Et Technology Of La Mer | Armi Z.,Institute National Agronomique Of Tunis | Turki S.,Institute National Des Science Et Technology Of La Mer | Trabelsi E.,Laboratoire Des Analyses Of Leau Of Mer | Ben Maiz N.,Laboratoire Des Analyses Of Leau Of Mer
Environmental Monitoring and Assessment | Year: 2010

Coolia monotis is a potentially toxic epiphytic dinoflagellate widespread along the Mediterranean coasts, where it is frequently detected year round at low concentrations. However, it only proliferates recurrently in some localities. The North Lake of Tunis is one of the affected areas in the southwestern part of the Mediterranean Sea. This site is one of the most productive aquatic Tunisian areas (Recreational Fisheries and shellfish collecting). In the south part of this area of study, recurrent C. monotis proliferation (5 ×10 5 cells per liter) took place in late spring and early summer of 2006. During this proliferation, the spatial distribution of C. monotis species, phytoplankton community, and abiotic factors were studied. The composition of the phytoplankton community exhibited a clear dominance of dinoflagellates over other genera. We suggest that proliferation development of C. monotis was linked to climatic conditions, water temperature (r=0.24, p<0.05) and high concentrations of nitrogenous nutrients, essentially NH 4 + (r=0.18, p<0.05) and NO 3 - (r=0.21, p<0.05). © 2009 Springer Science+Business Media B.V. Source

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