In a major pan-European study, a research team from Germany have successfully extracted environmental DNA (eDNA) from as many as 218 lakes to refute a long-year belief that vital microorganisms do not differ significantly between freshwater bodies and geographic regions the way plants and animals do.

Their new-age approach to biodiversity studies resulted in the largest freshwater dataset along with a study published in the open access journal Metabarcoding and Metagenomics.

Surface freshwaters are of critical importance for terrestrial life and, in particular, human life and welfare. However, these vital ecosystems are severely understudied, as compared to terrestrial or oceanic biomes, and so are the microbial organisms living in them.

On the other hand, it is these invisible to the naked eye creatures, called protists, that are responsible for keeping our ecosystems running. Their diversity and their high metabolic rates maintain ecosystem stability. In fact, microbes are the major source of the worlds oxygen.

In 2012, the team of Prof. Jens Boenigk, University of Duisburg-Essen, undertook the sampling campaign to study the distribution pattern of microbial organisms on a continental scale and the impact of Europe's climatic history on their present-day whereabouts.

They sampled freshwater lakes and ponds from sites in Norway, Sweden, Germany, Poland, the Czech Republic, Slovakia, Hungary, Romania, Austria, Italy, France, Spain and Switzerland. Site selection focused on the European orogens, specifically the Alps, the Pyrenees, the Apennine, the High Tatras, the southern Scandinavian mountains and the connecting flatlands.

Thanks to the excellent collaboration both within the team and with a number of scientific institutions across Europe, which gave their support as access points for re-stocking sampling equipment and immediate sample preservation, the campaign delivered groundbreaking results illuminating the hidden diversity of the microbial biosphere.

The scientists reported that plankton diversity was highly partitioned between lakes which bear distinct biological fingerprints. In particular, high mountain ranges imprinted the microbial communities on both regional and continental scale. Ecological factors, such as temperature and nutrient concentrations, are well accepted factors structuring plankton communities.

Beyond the high plankton diversity and the associated highly specific community composition in distinct lakes, the plankton community composition revealed signals of the past, i.e. since the last glaciation some 12,000 years ago.

While this expedition yielded many new scientific findings, the scientists note that these are only the first results of this continental survey.

"We are well aware that we have only just begun our exploration of the hidden diversity of plankton diversity," they conclude.