Temperature and salinity are some of the most influential abiotic parameters shaping biota in aquatic ecosystems. In recent decades, climate change has had a crucial impact on both factors—especially around the Antarctic Peninsula—with increasing air and water temperature leading to glacial melting and the accompanying freshwater increase in coastal areas. Antarctic soft and hard bottoms are typically inhabited by microphytobenthic communities, which are often dominated by benthic diatoms. Their physiology and primary production are assumed to be negatively affected by increased temperatures and lower salinity. In this study, six representative benthic diatom strains were isolated from different aquatic habitats at King George Island, Antarctic Peninsula, and comprehensively identified based on molecular markers and morphological traits. Photosynthesis, respiration, and growth response patterns were investigated as functions of varying light availability, temperature, and salinity. Photosynthesis–irradiance curve measurements pointed to low light requirements, as light-saturated photosynthesis was reached at <70 µmol photons m⁻² s⁻¹. The marine isolates exhibited the highest effective quantum yield between 25 and 45 S_A (absolute salinity), but also tolerance to lower and higher salinities at 1 S_A and 55 S_A, respectively, and in a few cases even <100 S_A. In contrast, the limnic isolates showed the highest effective quantum yield at salinities ranging from 1 S_A to 20 S_A. Almost all isolates exhibited high effective quantum yields between 1.5 °C and 25 °C, pointing to a broad temperature tolerance, which was supported by measurements of the short-term temperature-dependent photosynthesis. All studied Antarctic benthic diatoms showed activity patterns over a broader environmental range than they usually experience in situ. Therefore, it is likely that their high ecophysiological plasticity represents an important trait to cope with climate change in the Antarctic Peninsula.

In light of climate change, renaturation of peatlands has become increasingly important, due to their function as carbon sinks. Renaturation processes in the Baltic Sea include removal of coastal protection measures thereby facilitating exchange processes between peatland and Baltic Sea water masses with inhabiting aquatic organisms, which suddenly face new environmental conditions. In this study, two Baltic Sea and three peatland benthic diatom strains were investigated for their ecophysiological response patterns as a function of numerous growth media, light, and temperature conditions. Results clearly showed growth stimulation for all five diatom strains when cultivated in peatland water-based media, with growth dependency on salinity for the Baltic Sea diatom isolates. Nutrient availability in the peatland water resulted in higher growth rates, and growth was further stimulated by the carbon-rich peatland water probably facilitating heterotrophic growth in Melosira nummuloides and two Planothidium sp. isolates. Photosynthesis parameters for all five diatom strains indicated low light requirements with light saturated photosynthesis at <70 µmol photons m⁻² s⁻¹ in combination with only minor photoinhibition as well as eurythermal traits with slightly higher temperature width for the peatland strains. Growth media composition did not affect photosynthetic rates.

The intertidal zone of the Icelandic coast is characterized by strong seasonal and diurnal changes in the abiotic variables light, temperature and salinity, which are additionally affected by the tidal range and climate change. Iceland’s coastal zones host many phototrophic organisms including benthic diatoms that may strongly contribute as primary producers to the ecosystem functioning. However, studies on the ecophysiological responses to abiotic changes are rare. To better understand the impact of these variables, the influence on photosynthesis, respiration and growth of eight benthic diatom strains ( Navicula gregaria , Navicula jahniae , Navicula pseudoperminuta , Nitzschia olafsvikensis, Tryblionella ytritungaensis , Seminavis sp. and two strains of Navicula vesturlandica ) was comparatively investigated. Representatives of the different species exhibited distinct responses to the tested abiotic variables (light, temperature and salinity) with optimum photosynthetic and growth rates occurring between 5 and 30 °C. All strains exhibited a high photo-physiological plasticity reaching maximum photosynthesis between 11.9 and 105.8 µmol photons m ^-2 s ^-1 with no indication of photoinhibition at the maximum tested photon fluence rate of 1400 µmol photons m ^-2 s ^-1 . Strains of different taxa also showed specific responses to salinity, showing stenohaline and euryhaline (1 to 45 (65) S _A ) traits but with a common optimum for all species between 25 and 33 S _A , reflecting the conditions of their natural coastal habitat. Overall, these findings demonstrate the considerable ecophysiological plasticity of benthic diatoms from Iceland, that are required to withstand the environmental fluctuations in their natural habitat and to climate change driven variability.