Experimentelle Untersuchungen zur Ökologie der marinen Kieselalge Thalassiosira rotula. II. Der Einfluß des Salzgehaltes

Abstract

The effects of salinity (8 to 38‰) on the marine plankton diatom Thalassiosira rotula Meunier were investigated with respect to different temperature and light conditions. Two ecological aspects were examined separately: (1) the effect of various salinities, constant over a long period, was studied using well adapted cultures; (2) mixing processes were simulated by transferring cell chains from water of 33.9 or 20‰ S into lower salinities, as well as from 33.9 into 38‰ S. At 12° and 17°C, growth occurred at salinities from 12 to 38‰. In cold water (6°C), T. rotula did not grow below 16‰ S. Generation time was not influenced by salinities within the tolerance range if adapted cultures were grown under optimal illumination (1000 lux, light-dark cycle of 14:10 h; 12°C) or temperature (17°C; 2000 lux, light-dark cycle of 14:10 h). With increasing illumination or decreasing temperature, the other factors remaining constant, maximum growth rates were obtained with a salinity range of 20 to 32‰. Various salinities affected division rates most obviously if cultures were grown under continuous illumination; the optimum for cell division then ranged from 24 to 28‰ S only. Using adapted cultures again, the effect of different salinities on final cell yield is presumably more intense than their influence on generation time. T. rotula responded to sudden salinity changes only if transferred from water of 20‰ S into lower concentrations and from 33.9 into 38‰ S. Particularly at 12 and 38‰ S, growth rate and colony size (cells per chain) were reduced during the first few days. Increase of generation time and decrease of chain size occur coincidentally. The influence of different salinities on the occurrence of T. rotula in the sea is discussed in conjunction with experimental results on other ecological factors, and the present results are compared with the few available data obtained in nature by other authors. Accordingly, in the sea, a salinity range of 20 to 33‰ should prove optimal for T. rotula, 34 to 38‰ S would presumably represent still adequate conditions, while below 20‰ S T. rotula would probably rarely or never occur.