Popular Science: The microscopic inhabitants of Antarctic waters
This area is, in the context of Antarctica, pleasant for life, because it isn’t continuously covered with snow, and in summer, water from melting glaciers forms streams, ponds and lakes. Thanks to the fact that many of them don’t freeze, life is possible there. The first samples of algae living there were collected as early as 1907. Yet we are still talking about Antarctica – these ponds actually represent what may be one of the thresholds for life on Earth, because if they were only a bit harsher, it would be difficult for anything to live there at all. Our researchers focused on Antarctic diatoms.
Diatoms are charming photosynthesizing organisms building silica enclosures. There are both marine and freshwater species, very common and very important for the production of oxygen on Earth. They are easy to identify under a microscope, and their diversity is rather low (only about 50 species). These qualities make them a suitable study subject.
Samples were collected from 25 ponds, each characterized by different conditions: some had an ice cover, some did not. A part of them was connected by streams with other ponds, a part was isolated. Salinity and pH differed. The task was to find out how rich in species these freshwater Antarctic ponds were. Researchers found about 45 species of diatoms. Some were known by the end of the 19th and beginning of the 20th century, others were discovered only recently, and there were even species unknown before and seemingly endemic.
The distance between ponds was much more important in explaining the species present in the ponds than the actual characteristics of the ponds. Ponds close to each other were more similar to each other, despite their differences in physical and chemical characteristic. Interestingly, some diatoms inhabited environments very untypical for them. For example Navicula adminii was up until now seen only in marine, especially cold ocean water. However, here it settled in the least saline pond in the area. On the other hand, Craspedostauros laevissimus preferred strictly brackish water – places were marine and fresh waters mix. In the observed area, it inhabited only saline or freshwater ponds, and avoided the brackish ones. This phenomenon is difficult to explain; however, it is clear that many diatom species are capable of surviving in conditions very different form their optimum.
Diatoms are typically transported on the fur of mammals or feathers of birds – quite a problem in Antarctica. There are only two big enough species – South polar skua and Adélie penguin – and even these are present only for a part of a year. This means that the diatoms have to rely on wind, and in summer also on melting ice. The researches argue that the connection of many ponds by streams of melting ice can explain finding similar species in ponds close to each other in distance rather than physical and chemical characteristics, and the presence of species in conditions untypical for them. The lack of other transport vectors such as animals could be the reason of diatoms’ limited ability to spread to further locations.
Evidence for dispersal and habitat controls on pond diatom communities from the McMurdo Sound Region of Antarctica; A. Sakaeva, E. R. Sokol, T. J. Kohler, L. F. Stanish, S. A. Spaulding, A. Howkins, K. A. Welch, W. B. Lyons, J. E. Barrett, D. M. McKnight; Polar Biology; 2016