Microbes and the groundwater amphipod Crangonyx islandicus in spring sources in Iceland

Abstract

Crangonyx islandicus is a groundwater amphipod endemic to Iceland. Genetic analysis suggests that the species has been diverging in Iceland for at least 4.8 Myrs indicating it has survived in a subglacial refugia as Iceland was repeatedly covered by glaciers during that time period. The species has probably been inhabiting Iceland since before the island was formed, when the land bridge to Greenland collapsed into the ocean approximately 15 Mys ago. Currently, their habitat is in the subsurface of spring sources within the lava fields along the tectonic plate boundary. These spring sources act as a window into the groundwater, but they are also a complex ecotone where groundwater mixes with surface water and the terrestrial ecosystem. In this thesis, the microbial community composition associated with the amphipods and their habitat was examined both to inspect if more taxa could be found in this unique habitat and to elucidate which processes are likely to shape the community composition of microbial species in the habitat. The results showed that the amphipods are accompanied by a few ciliate and bacteria taxa that are unique to these amphipods but can only be marginally detected in the spring source. Both stochastic and deterministic processes were found to shape the bacteria and ciliate communities in the spring source. Variables such as pH, temperature, presence of fish and geographical location were found to shape the bacterial community while temperature and dispersal was shaping the ciliate communities. The bacterial community in the water from spring sources and in the biofilms harbored chemolithoautotrophic taxa, indicating primary production in the groundwater system, thus, providing a possible explanation for the subglacial survival of the amphipods during Ice age.