Limnology and Aquatic Microbial Ecology of Byers Peninsula: A Main Freshwater Biodiversity Hotspot in Maritime Antarctica

Abstract

Here we present a comprehensive review of the diversity revealed by research in limnology and microbial ecology conducted in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) during the last two decades. The site constitutes one of the largest ice-free areas within the Antarctic Peninsula region. Since it has a high level of environmental protection, it is less human-impacted compared to other sites within the South Shetland archipelago. The main investigations in Byers Peninsula focused on the physical and chemical limnology of the lakes, ponds, rivers, and wetlands, as well as on the structure of their planktonic and benthic microbial communities, and on the functional ecology of the microbial food webs. Lakes and ponds in Byers range along a productivity gradient that extends from the less productive lakes located upland to the eutrophic coastal lakes. Their planktonic assemblages include viruses, bacteria, a metabolically diverse community of protists (i.e., autotrophs, heterotrophs, and mixotrophs), and a few metazooplankton species. Most of the studies conducted in the site demonstrate the strong influence of the physical environment (i.e., temperature, availability of light, and water) and nutrient availability in structuring these microbial communities. However, top-down biotic processes may occur in summer, when predation by zooplankton can exert a strong influence on the abundance of protists, including flagellates and ciliated protozoa. As a consequence, bacterioplankton could be partly released from the grazing pressure exerted by these protists, and proliferates fueled by external nutrient subsidies from the lake’s catchment. As summer temperatures in this region are slightly above the melting point of water, biotic processes, such as those related to the productivity of lakes during ice-free periods, could become even more relevant as warming induced by climate change progresses. The limnological research carried out at the site proves that Byers Peninsula deserves special attention in the framework of the research in extreme environments. Together with nearby sites, such as Signy Island, Byers Peninsula comprises a featuring element of the Maritime Antarctic region that represents a benchmark area relative to the global distribution and diversity of aquatic microorganisms.

Functional Metabolic Diversity of Bacterioplankton in Maritime Antarctic Lakes

“…This is the case for β-methyl-glucoside (C3), which is a monosaccharide derivate from glucose by acid degradation and decomposition processes, that is especially relevant in lakes Refugio and Somero. Vegetation from the catchments, that is composed principally by microbial mats and terrestrial mosses, provides an important supply of organic carbon for these lakes, particularly during the onset of the summer season because of the intense run-off processes produced when the snow melts [5]. Accordingly, it is expected that there is a close link between these plant and algal materials and the metabolic capabilities of bacteria to degrade them.…”

“…This compound is an oxidized monosaccharide form of D-galactose that is present in the mucilage produced by the cyanobacterial microbial mats [58]. Microbial mats cover part of the catchment of Lake Limnopolar [53] and constitute an important source of allochthonous carbon to the lakes [5]. D-malic acid (CA9) is a dicarboxylic acid which is produced by living organisms.…”

“…The lake depth regulates the relative importance of the pelagic and benthic habitats, whereas the external nutrient inputs determine its trophic status [35]. The deeper inland lakes (<3 m) may show well-developed or patchy bottom moss carpets of Drepanocladus longifolius, however, these benthic mosses do not appear in the shallower lakes, which otherwise may show phototrophic microbial mats in their catchments or form a ring in the lake shore [5]. Among inland lakes, some catchments, such as those of lakes Chester and Midge, show a lower percentage of vegetation (both mosses and microbial mats) coverage compared to others, such as lakes Limnopolar and Somero.…”

“…The diversity and distribution of planktonic microbial assemblages in maritime Antarctic lakes have been widely studied during the last decades [1][2][3][4][5]. Maritime Antarctic lakes display a biological community mainly dominated by microorganisms [6][7][8][9][10], where bacterioplankton performs a key role [11].…”

“…Current knowledge of aquatic ecosystems in Byers Peninsula, located in the South Shetland Islands (maritime Antarctica), is among the most complete and exhaustive for any place within the whole of Antarctica, as recently summarized by Rochera and Camacho [5].…”