Regulation of life history in the brackish cladoceran, Daphniopsis australis (Sergeev and Williams, 1985) by temperature and salinity

Temperature and salinity variations affect aquatic biodiversity by altering the life history of poikilotherms and regulating their population dynamics. This study aimed to reveal the response of the brackish cladoceran, Daphniopsis australis exposed to three temperatures (16, 20 and 25°C) cross-classified with three salinities (17, 22 and 27). Our results show a significant interactive effect of temperature and salinity on most life history variables. The individual parameters including longevity, total egg clutch, egg development time, offspring production and total moulting were negatively related to the elevations of temperature and salinity. High salinity dampened the positive relationship between age at first reproduction and increasing temperatures. Population parameters including age-specific survivorship, age-specific fecundity, net reproductive rate and generation time were negatively affected by the increasing temperature and salinity. The intrinsic growth rate showed a unimodal distribution with peak population growth occurred at 20°C and 22 salinity, indicating the optimal condition for population growth. The poor performance of growth, reproduction and development occurred at 25°C and 27 salinity. Considering the dual effects of thermal and saline fluctuation, the life history of D. australis is more greatly impacted by temperature rather than salinity, which can contribute to the explanation of seasonal dynamics of brackish water cladocera in salt lakes.