The Influence of Environmental Factors on the Population Structure and Reproductive Biology of <i>Idotea balthica basteri</i> (Isopoda, Valvifera) of the Bizerte Lagoon (Northern Tunisia)

Abstract

The reproductive biology of a natural population of Idotea balthica basteri (Pallas, 1772) collected from Menzel Jemil (Bizerte lagoon, Tunisia) was monthly studied from October 2009 to October 2010. Besides water temperature, salinity, turbidity, pH, and dissolved oxygen were measured. Based on the state of differentiation of individuals, the population was divided into 8 categories. Their numbers depend on the one hand to intrinsic factors imposed by the specimens and the structure of the population themselves, and to extrinsic factors due to the variability of environmental conditions on the other hand. Females were morphologically recognisable at smaller size than males. Reproductive activity, which was reflected through the presence of ovigerous females and juveniles, underwent fluctuations throughout the year, but it was continuous. Moreover, salinity, temperature, nitrates, and plant biomass have a noticeable effect on the fecundity and fertility. The Principal Component Analysis also confirmed that the richness of the water in nitrates would be favorable to fecundity and fertility of Idotea balthica basteri . However, higher phosphate concentrations, in April and May seem to have a positive effect on the sex ratio. Otherwise, the temperature would be responsible for increasing the percentage of ovigerous females.