 Schmidt worked in parallel on phycology, where he described the genus "Richelia" (filamentous heterocyst-forming Cyanobacteria dwelling inside diatoms), on plant physiology and genetics, especially of hops, and on large-scale oceanography and ichthyology.Beginning in 1904, Johannes Schmidt led a series of expeditions into the Mediterranean Sea and the North Atlantic to investigate eels.In 1928–1930, he led the Dana Expedition, funded by the Carlsberg Foundation, being a two-year voyage around the world's oceans.