Influence of seawater salinity on the survival, growth, development, and neonate production of Scapholeberis mucronata (O. F. Müler) (Crustacea: Cladocera)

In order to determine the influence of of salinity on the survival, growth, development, and neonate production of the cladoceran Scapholeberis mucronata (O. F. Müler), long-term experiments were carried out at four salinity gradients (1, 2, 3, and 4) and a control (freshwater) using Chlorella pyrenoidesa as feed. The acute effect of salinity on this species indicated that salinity gradients 4 and 4.5 were its upper tolerance limits for reproduction and survival. The survival and growth rates of individuals reared in salinity gradients 1 and 2 were higher than those reared in other salinity gradients. The mean size of the female adults decreased from 820 to 743 μm when the salinity increased from salinity gradients 1 to 4. For individuals reared in salinity gradients 1 and 2, the r m of population was 1.021 and 0.903, respectively; the rate of egg production was 1.281 and 1.390, respectively; the cumulative egg production was 83.2 and 106.0 and mean life span was 16.05 and 17.30, respectively. These values of life-history parameters were higher than those of individuals reared in salinity gradient 3. No eggs were produced by females reared in gradient 4 during the entire experiment. Furthermore, individuals reared at gradients 1 and 2 had faster embryonic development. The above results imply that S. mucronata prefer an environment with lower salinity (1-2). Resting egg formation and sexual reproduction did not occur in any of the tested salinity gradients.