Abundance and biomass of rotifers in relation to the environmental factors in geothermal waters in Southern Tunisia

The spatial and temporal dynamics of rotifers in relation to the physico-chemical parameters in Fish-Culture Research Station (Southern Tunisia) were studied monthly from February 2005 to January 2006. Thirteen rotifer species were found: Brachionus urceolaris, Brachionus calyciflorus, Brachionus sp., Lecane stichaea, Lecane rhytida, Lecane sp., Hexarthra mira, Rotaria tardigrada, Conochiloides natans, Trichocerca marina, Keratella quadrata, Keratella cochlearis and Notommata codonella. The most dominant rotifer was B. urceolaris (76% of total abundance). Rotifer density and water temperature were negatively correlated (r=−0.94, n=12, p=0.001). The highest abundance of rotifers was found in basin 4 (1.5×105 ind m−3, in June 2005).