Contribution of Crenarchaeota and Euryarchaeota to the prokaryotic plankton in the coastal northwestern Black Sea

The NW Black Sea is an area with peculiar hydrological, hydrochemicaland biological features (river plume dynamics, coastal upwelling,intense eutrophication, blooms algae). We determined the abundanceand distribution of the two major groups of Archaea (Crenarchaeotaand Euryarchaeota) in three contrasting sites of the NW BlackSea from May to August 2004 to estimate the contribution ofnon-extremophilic Archaea to the coastal prokaryotic plankton.Using catalyzed reporter deposition-fluorescence in situ hybridization,Euryarchaeota were found to be particularly prominent (11–22%of total prokaryotic plankton) in the low-salinity waters duringlate-spring and summer, whereas Crenarchaeota contributed only5% to the prokaryotic community in these waters. The abundanceof Crenarchaeota was highest in nutrient- and particle-richwaters and lowest in offshore Black Sea surface waters. Theseresults confirm recent studies on the distribution of planktonicArchaea with Euryarchaeota dominating the archaeal communityin surface waters. Statistical analyses indicated significantcorrelations between crenarchaeotal abundance, ammonia and nitrateconcentrations at each sites. Our data show that the archaealplankton constitute an important and dynamic component of theprokaryotic plankton in the coastal oxygenated waters of theNW Black Sea and might play a significant role in the nitrogencycle.