Abundance and biomass of prokaryotic and eukaryotic microorganisms coupled with environmental factors in an arid multi-pond solar saltern (Sfax, Tunisia)

Abstract

International audienceThe distribution of abundance and biomass of prokaryotes, flagellates, ciliates and phytoplankton, were studied in five ponds of increasing salinity in the Sfax solar saltern (Tunisia) coupled with environmental factors. The results showed that abundance of eukaryotic microorganisms decreased with increasing salinity of the ponds whereas prokaryotes (heterotrophic bacteria and Archaea) were abundant in the hyper-saline ponds. Phototrophic picoplankton was found in a large range of salinity values (70 and 200‰). Phototrophic non-flagellated nanoplankton which dominated in the first sampled pond was substituted by phototrophic flagellated nanoplankton in the other ponds. Heterotrophic nanoplankton dominated in the crystallizer pond but its quantitative importance declined in the less saline ponds. Diatoms and dinoflagellates were the major contributors to phytoplankton abundance in the first ponds (.90% of total abundance). Ciliated protozoa were found in all the ponds except in the crystallizer in which prokaryotes proliferated. Oligotrichida and Heterotrichida were the most abundant ciliate groups. Overall, species richness decreased with salinity gradient. We propose a simplified diagram of the Sfax saltern's food web showing the dominant role of the microbial loop along the salinity gradient

Impacts of restoration of an uncontrolled phosphogypsum dumpsite on the seasonal distribution of abiotic variables, phytoplankton, copepods, and ciliates in a man-made solar saltern

“…Consequently, Tunisian authorities undertook the Taparura project in 2006 to attack the phosphogypsum pollution at its source, to clean the ponds of an excess of macrophytes and to generally improve the regional environment. We (Abid et al 2008;Elloumi et al 2009; Khemakhem et al 2010) and others (Joint et al 2002;Oren 2005) have shown that salterns harbor a variety of organisms ranging from marine like to extreme halophiles and hypothesized that this restoration might lead to a change in the composition of the saltern's biological communities located near the phosphogypsum landfill. Salterns are, in some regards, well-studied systems (Oren 2005;Elloumi et al 2009), yet aspects associated with anthropogenic impacts, especially from phosphogypsum residues on biological communities, have never before been reported.…”

“…We (Abid et al 2008;Elloumi et al 2009; Khemakhem et al 2010) and others (Joint et al 2002;Oren 2005) have shown that salterns harbor a variety of organisms ranging from marine like to extreme halophiles and hypothesized that this restoration might lead to a change in the composition of the saltern's biological communities located near the phosphogypsum landfill. Salterns are, in some regards, well-studied systems (Oren 2005;Elloumi et al 2009), yet aspects associated with anthropogenic impacts, especially from phosphogypsum residues on biological communities, have never before been reported. This lack of information may be explained by (1) the major cost and time constraints placed on this kind of study by the sorting and identification of the species present and (2) the hardship of discriminating between stress due to the salt gradient and that caused by phosphogypsum residues.…”

“…Temperature and pH were measured in situ using a mercury glass thermometer graduated in 0.1°C and a Metrohm ® type pH meter. Salinity, as totally dissolved salts, were estimated by the dry residue method, which consists of evaporating a 50 ml sample (24 h, 180°C) in a previously sterilized crystallizing dish (by heating at 550°C for 1 h), and calculating the salt content from the difference in weight before and after evaporation (Elloumi et al 2009). Concentration of suspended matter was determined by measuring the dry weight of the residue after water filtration through a Whatman GF/C membrane.…”

“…In addition, the saltern had experienced the development of two green macroalgae (belonging especially to the genera Enteromorpha and Cladophora)and one red alga (Chondria) whose decomposition, along with that of the leaf waxes of land plants, had led to foul odors and an unpleasant appearance. The ponds, interconnected by pipes and channels along a 12-km stretch of seacoast, thus required significant expense and effort for maintenance and cleanliness (Elloumi et al 2009). Consequently, Tunisian authorities undertook the Taparura project in 2006 to attack the phosphogypsum pollution at its source, to clean the ponds of an excess of macrophytes and to generally improve the regional environment.…”

Space-time variation of ciliates related to environmental factors in 15 nearshore stations of the Gulf of Gabes

“…This is reflected by the presence of substantial amounts of halotolerant Hetrotrichea F. salina (9.2 % of the ciliate total abundance), in Karboub samples, a species that was also found in high abundance in the primary ponds of Sfax saltern (Elloumi et al, 2008), yet in higher salinities (range . This change in ambient salinity resulted in smaller F. salina at the Karboub station (length = 75 µm; biovolume = 44.3 µm 3 ) than in the Sfax saltern (length = 111 µm; biovolume = 108.1 µm 3 ) (Elloumi et al, 2006(Elloumi et al, , 2009b. We assume that the size of F. salina may have been indirectly rather than directly related to salinity.…”