Spatial and temporal variations of microphytoplankton composition related to hydrographic conditions in the Gulf of Gabès

Abstract

11 pagesInternational audienceThe spatial and temporal variations of the microphytoplankton communities were examined during four oceanographic cruises conducted between July 2005 and March 2007 aboard the RV ‘Hannibal'. Water thermal stratification started in May–June, and a thermocline established at 20 m depth, but ranged between 25 m during July and more than 30 m during September. The high concentrations of chlorophyll a were observed during the May–June semi-mixed conditions and were mainly correlated with the concentrations of phosphate, suggesting a potential limitation by this nutrient. The Bacillariophyceae were dominant in the coastal samples, whereas they declined in the offshore area, most likely due to silicate shortage. Cyanobacteriae developed over semi-mixed conditions and at the thermocline depth. Relatively constant abundance of dinoflagellates was observed during the sampling periods from the coast to the offshore area, mainly explained by the high diversity species of this group. The results suggest that some phytoplankton taxa are generally adapted to specific hydrological conditions, whereas the dinoflagellates did not seem to follow this trend. Our findings have important biogeochemical implications in relationship with the export fluxes of the particulate matter throughout the water column

Spatial and seasonal variability of pico-, nano- and microphytoplankton at the bottom seawater in the north coast of Sfax, Eastern Mediterranean Sea

“…These genera were reported to be present under high phosphate availability (Satsmadjis and Frigilos 1983;Costas and Lopez-Rodas 1991) and were observed in the Gulf of Tunis under high phosphate concentrations and reduced nitrogen resources, suggesting that the proliferation of dinoflagellates was mainly phosphate-driven (Daly-Yahia Kéfi et al 2005). In particular, the continuum of dinoflagellates may be explained by the cell motility allowing them to explore different depths (Drira et al 2009). Seasonal variations of microphytoplankton abundance in the bottom were mainly driven by nutrient and hydrological features during each season.…”

Functional diversity of the macro‑invertebrate community in the port area of Kerkennah Islands (Tunisia)

“…In general, the important industrial, urban and maritime development along the littoral of the Gulf of Gabès has lead to an increase of pollution, impacting marine systems and changing the structure and functioning of benthic communities (Hamza et al, 2000). Several faunal groups have been recently studied in the Gulf of Gabès, such as the summer phytoplankton bloom (Bel Hassen et al, 2008;Drira et al, 2009) and the copepod (Drira et al, 2010) and ciliate distribution (Kchaou et al, 2009), but data on benthic macro-invertebrates are lacking.…”

Spatial Distribution and Source Identification of Heavy Metals in Surface Waters of Three Coastal Areas of Tunisia

“…This area has been subjected to increasing pressure linked to the development of several activities on the coast and in the sea. The Gulf of Gabes (southwestern Mediterranean) is one of the most vulnerable aquatic ecosystems, contributing about 65% of national fish production in Tunisia [32][33], fauna biodiversity [34][35][36][37][38] and a wide distribution of Posidonia Oceanica, an endemic species representing a good nursery for fish eggs and larvae [39]. However, due to the increase of urbanization, industry, overfishing, tourism, and the discharge of huge amounts of phosphogypsum and other pollutants, the Gulf of Gabes has been reported to be densely polluted [40].…”