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.

Diatoms are of major importance in marine and freshwater systems, but their occurrence in terrestrial situations is generally thought to be exceptional. Following up on the accidental discovery of epiphytic diatoms on bark samples in an unrelated study, we investigated their presence in the tropical lowlands of Panama more systematically using scanning electron and light microscopy. We sampled inundated and aerial bark portions of Annona glabra, a tree that grows along the shore of Lake Gatun, and took bark samples from other tree and liana species at c. 1.5 m height in the forest understory. In total, we found 70 diatom taxa in 28 genera. Species numbers and composition differed among the three microhabitats with the largest numbers on inundated bark portions, but even in the forest understory, we found 12 taxa with densities of up to 900 frustules per mm⁻² of bark. Our data set is still quite limited in scale but the results suggest the possibility that hitherto unacknowledged assemblages of epiphytic diatoms may be quite common in wet tropical forests, which clearly warrants further study.