Salt tolerance of Rana temporaria: spawning site selection and survival during embryonic development (Amphibia, Anura)

Abstract

Spawning site selection of Rana temporaria is dependent on the salinity of the water. In the nature reserve 'Salzwiesen von Münzenberg' (Germany) the frogs avoided increased conductivity values, Cl- ion concentrations and salinities and selected lower values for spawning. In the laboratory Gosner stages 20/21 to 22/23 were more sensitive to sodium than the earlier G stages 8 to 20/21 (exposition for 72 h) though they were exposed for the shorter time period of 24 h. The 'no observed effect concentration' (NOEC) between G stages 8/9 and 20/21 was 648 ppm (3350 μS, 2.2‰ salinity) for Na+ and 1872 ppm (6500 μS, 4.0‰ salinity) for K+. The NOEC between G stages 20/21 and 22/23 was 1490 ppm (7400 μS, 4.5‰ salinity) for Na+ and for K+ also 1872 ppm (6500 μS, 4.0‰ salinity). All developmental stages tolerated much higher ion concentrations and conductivity values in the laboratory than the adult frogs selected for spawning.