Introduction of the technical diving method for scientific diving to investigate biocoenosis in the twilight zone of freshwater lakes

The existence of light-dependent (zooxanthellate) corals at depths between 40 to 150
meters (sometimes up to 300 meters) has been known since the nineteenth century
and they are specifically called mesophotic coral reef (MCR) ecosystems. Their
systematic study began about 50 years ago, but just in the last decade, mainly due to
the development of new diving techniques, these deep coral reefs have been
extensively studied.
Also from the Mediterranean Sea new communities in these depths - the twilight zone
- are described again and again. For example, a veritable underwater forest of black
corals (Antipathella subpinnata) was recently discovered from the Adriatic Sea
(Tremiti Islands) between 52 and 80 meters of water depth.
A description of biotic communities in the twilight zone in freshwater systems, such
as on steep walls, is searched in vain in the relevant literature. Detailed observations
and characterization of mesophotic, almost lightless communities, e. g. of the steep
walls in Lake Constance between 40 and 150 meters, are missing so far.
We present first dives into these area (40 – 100 meters) using the example of the
... mehr
steep walls of Lake Constance (Überlinger See), describe the necessary diving and
sampling techniques and skills.
To our knowledge, these are the first scientific dives into these depth ranges in
freshwater lakes.