Strategic population responses of Daphnia spinulata Birabén, 1917 to salinity changes through laboratory bioassays

Abstract

Zooplankton play a key role in aquatic ecosystems constituting an essential intermediate component in aquatic food webs. Cladocerans in particular are widely studied as model of generalist filter feeders. At the regional level, the cladoceran Daphnia spinulata is found in numerous habitats with wide conductivity range (160 μS cm−1 to 14.000 μS cm−1), but information about the species's tolerance range or life history is scarce. Our objective was to generate essential information about D. spinulata's life history and the main parameters related to two contrasting salinity levels representative of water bodies of the pampean plain. Results obtained in laboratory bioassays showed that individuals at low conductivity (700 μS cm−1) had more moults, a lower mortality and a higher life expectancy at birth, a higher generation time, and an earlier peak density than those at high-conductivity treatments (5000 μS cm−1). The maximum density reached was similar for both conductivities indicating a similar growth capability attained by different strategies. Moreover, the results indicated that D. spinulata at different conductivities was able to reproduce, with the offspring thus contributing to population growth. This study provided a knowledge of the life history strategies of this endemic cladoceran at two different conductivities, thus generating crucial information on the population dynamics and for evaluating the species's role as a possible salinity indicator in pampean water bodies. Nevertheless, future investigations will be necessary in order to identify the absolute limits of tolerance and the optimum conductivity for this species and determinate which stressors will act as a mictic stimuli.