Growth responses of 25 benthic marine Wadden Sea diatoms isolated from the Solthörn tidal flat (southern North Sea) in relation to varying culture conditions

Abstract

The unconsolidated sediment of intertidal mudflats constitutes a highly unstable environment, due to continuously changing water levels and currents, as well as temporary exposure to the air. As a consequence, diatoms inhabiting marine intertidal areas are subjected to wide variations in temperature, surface light intensity and salinity due to exposure at low tide. In order to determine the adaptive potential of these organisms, cultures of 25 benthic marine diatom species present in the Solthörn tidal flat in the years 2008/2009 were chosen to study the effect of different abiotic conditions. As expected, the interspecific growth rates between individual species varied considerably, from 0.181 d−1 [Gyrosigma peisonis (Grunow) Hustedt] to 0.861 d−1 [Navicula phyllepta (Kützing)], while the intraspecific growth rates were only slightly influenced by most of the tested variables. In detail, individual effects were found for different substrates (mixed glass beads, mixed sands, none), nitrogen sources (nitrate, urea, ammonium), photon flounce rates (400, 800 and 1200 μmol photons m−2 s−1) and day lengths (light:dark cycle, 8:16, 12:12, 16:8 h); whereas variations in salinity from 20 to 35 PSU and temperature from 10 to 30 °C did not show any influence on benthic diatom growth. By contrast, extreme temperatures (4, 40 °C) and salinities (10, 40 PSU) led to significant decreases in the growth rates of most species. Only minor effects on the growth of Navicula spp. in the 10 PSU treatments were distinguishable, e.g., N. digito-radiata (Gregory) Ralfs. All in all, the adaptation potential of the Solthörn tidal flat isolates in relation to the tested environmental ranges was appreciable, suggesting special intracellular adaptation processes that provide possible explanations for the species’ insensibility towards environmental variations and distinct differences in the diatom assemblages.