Influence of salinity on seasonal germination of resting stages and composition of microplankton on the Swedish west coast

Abstract

Surface sediment from Gullmar Fjord, Sweden was cultured in the laboratory to assess the influence of different salinities on the germination of benthic resting stages and subsequent veg- etative growth. Sediment cultures were grown in media with salinities of 15, 25, and 35‰ in both spring and summer conditions. Many microplankton species grew in the cultures. Dominant taxa were the diatoms Chaetoceros, Detonula, Skeletonema, and Thalassiosira, and the dinoflagellates Diplopsalis, Scrippsiella, and Oblea. Growth of T. minima and T. pseudonana after more than 2 yr of storage provides new evidence of a dormant stage in these species. Salinity significantly influenced germination only in D. confervacea and O. rotunda, but it showed significant effects on growth for all the dominant taxa. Salinity optima of the microplankton in the experiments were compared to salin- ity ranges of these species in fjords on the Swedish west coast. In the fjords, D. confervacea grows poorly at salinities >27‰ and may be outcompeted by halotolerant species, such as C. socialis and T. minima. Because salinity is most variable in spring, a wide salinity tolerance is particularly advanta- geous during this season. The dominant dinoflagellates were well adapted to salinities between 22 and 35‰, and O. rotunda is favored at the high end of this range. Results illustrate how climate- related changes in sea-surface salinity may alter the microplankton community on the Swedish west coast through direct effects on resting-stage germination and planktonic growth.