By D. S. Brown
Dr Georg Mandahl-Barth died at his home on the west coast of Denmark, on the 19th April 1994, in his eighty fourth year. His publications on the Mollusca were mostly on the taxonomy of freshwater gastropods and bivalves of Africa. He was well known internationally for his monographic revision of the planorbid genera Biomphalaria and Bulinus (1957, 1958). These snails are of medical importance, for some species serve as intermediate hosts in the life cycle of parasites belonging to the trematode genus Schistosoma, which complete their development as blood parasites of man, causing the disease schistosomiasis (bilharziasis).
Born in Copenhagen in 1910, the nine-year old Georg barely survived a serious infection of his ear, which left him with a damaged jaw and poor hearing. While in hospital he overheard a nurse say to his mother that it would be best for him to die, as if he survived he would surely be mad. The boy became intensely interested in natural history and in his 14th year his attention was switched from moths to molluscs, when he found a shell that he thought was a new green-coloured species of Helix, but which turned out to be a long dead specimen of nemoralis covered with algae. He filled notebooks with hundreds of pencil drawings of shells copied accurately from books, and thus acquired the skill with which he later would illustrate his own publications. Passing the entrance exam to the University of Copenhagen in classical languages, Mandahl-Barth then studied Zoology, gained his Master’s degree in 1936 and became a temporary assistant in the University Museum. Disappointed at not obtaining a permanent post there, he accepted the appointment as Inspector (Deputy Director) of the recently-opened Dansk Akvarium at Charlottenlund, a northern suburb of Copenhagen.
Mandahl-Barth continued his molluscan activities, working on the dining table in his residential flat above the Akvarium. His study of the landsnails of Madeira was accepted as a doctoral thesis by the University of Copenhagen in 1943 and sent to Frankfurt for printing. Publication was delayed for 7 years, however, at first due to the destruction of printing presses by the wartime bombing, which obliged him to correct proofs no less than seven times. Then the manuscript was sent to Luxembourg, where it was impounded by a printer as 'spoils of war'.
In the 1940s Mandahl-Barth turned his attention to the molluscs of Africa and by the early fifties he had identified several collections of freshwater snails obtained during early surveys of schistosomiasis transmission, sponsored by the World Health Organisation. He visited Uganda in 1951 to make collections, in collaboration with his compatriot Cai Cridland, then at the East African Fisheries Organisation, Jinja. This was the only substantial field work carried out in Africa by Mandahl-Barth; for other materials he depended on numerous collectors, among whom may be mentioned C. C. Cridland, P. L. LeRoux, F. S. McCullough, C. Ripert and J.J. Symoens. In 1952 the WHO awarded to his services, still performed in his home, the title "WHO Snail Identification Centre". By the late 1950s Mandahl-Barth was the leading authority on the freshwater molluscs of Africa. Impressed by this achievement, the Knud Hølgaard Foundation (founded by wealthy Danish engineer) granted funds for the construction, near to the Akvarium, of a laboratory to be devoted to the study of schistosomes and their snail intermediate hosts. This opened in 1964, as the Danish Bilharziasis Laboratory (DBL), with Mandahl-Barth as Director. When he retired from the DBL in 1978, the research carried out there in malacology and parasitology had achieved a high reputation, providing the foundation from which has developed the present major centre concerned with several water-related parasitic diseases in the tropics.
I was fortunate to know Georg Mandahl-Barth for over 30 years. From the beginning of our friendship, at the Akvarium in 1963, he gave me the freedom of his collection and library, and I benefitted also from his guidance to the classic molluscan literature. Without his early encouragment, which nurtured my interest in the large fauna of African freshwater gastropods besides those of medical importance, I probably would not have attempted the broad systematic synopses in my own books.
Mandahl-Barth was a good general naturalist. Familiarity with Greek and Latin gave him a scholarly pleasure in nomenclature, and he was fluent in several modern languages (four different ones were used in his first six publications). He spoke English with precision, wit and a dry humour, and was appreciative of English pipe tobacco. Although polite and kindly, he did not enjoy public occasions and hardly ever attended a scientific meeting. He was reluctant to travel even so far as central Copenhagen, and told me that he would have preferred the DBL have been built on a remote part of the Jutland coast, reachable by only the most determined visitors. This reclusiveness was partly because he carefully guarded his time against trivial activities, as he saw them. He was reluctant to devote time to an investigation after he had satisfied his curiosity and he was not much concerned about communicating his findings in print. He met his wife-to-be, Gudrun, while they both were students and they celebrated their Golden Anniversary shortly before her death in 1990. She constantly supported him by providing a quiet domestic routine, allowing Georg the maximum time for his varied interests, including the nightly operation of a light-trap for moths.
In his taxonomic investigation of gastropods, Mandahl-Barth was interested in a limited number of gross features, including the radula, copulatory organ and, above all, the shell. Likewise for bivalves, it was the shell that received most of his attention. His memory was extraordinarly and he seemed to know the exact position of each of thousands of tubes and boxes in his shell cabinets. He was not much impressed by the methods of experimental taxonomy, such as enzyme electrophoresis, for defining species. His opinions were expressed forthrightly, as when he asked me to tell my colleague Christopher Wright that the unusual cusps of the radula that Wright had described for a species of Bulinus were impossible. Rather annoyed, Wright immediately sent specimens for Mandahl-Barth to examine himself. Finding the cusps to be just as Wright had described, Mandahl-Barth apologised graciously and established these snails as the new taxon B. reliculatus wrighti, later recognised as a distinct species.
Outstanding publications produced during Mandahl-Barth's years at the DBL were revisions of the prosobranch genus Potadoma (1967) and the Bithyniidae (1968), and general faunal studies of the Bangweolo-Luapula region (1968), Lake Malawi (1972), south east Zaire (1972) and lower Zaire (1974). In addition he wrote anonymously a series of regional field guides for the identification of African freshwater snails, issued by the DBL in the 1970s. After retirement he was free to devote more time to bivalves, which he perhaps preferred to gastropods, but it seemed probable that his findings accumulated over 30 years would still remain unpublished. Fortunately the willingness of former colleagues at the DBL, Thomas Kristensen and Elaine Svenningsen, to edit his notes encouraged him to assemble his 'Studies of African freshwater bivalves' (1988), whch ranks among his most important contributions.
Mandahl-Barth was also the author of a series of highly successful popular books on European wildlife, originally published in Danish. The first appeared in 1955 and dealt with fresh water, later subjects included forest and seashore. The combination of concise text, fine artwork in colour by Henning Anthon and low price produced large sales, numerous reprintings and translations into several other languages, including English (e.g. Woodland Life, Blandford Press, London, 1966).
During the early 1940s Mandahl-Barth observed that Helisoma, a planorbid of North American origin that is distributed widely over the world through the transportation of aquatic plants, was superceding Biomphalaria in the exhibition tanks of the Akvarium. Experiments he made in the 1960s led him to suggest that Heilisoma produced some substance that inhibited the development of eggs and growth of other snails. The possibility of using a competing snail control intermediate hosts for schistosomes, rather than chemical molluscicides, attracted widespread interest, and in 1975 Mandahl-Barth was awarded a substantial prize by the medical company NOVO Nordisk. Although further research failed to confirm the existence of an inhibitory substance, the competitive superiority of Helisoma is real, and seems due to competition for food and physical stress to a 'weaker' species. The competitor is still a candidate for controlling intermediate host snails if standard procedures could be developed for establishing it under field conditions.
Mandahl-Barth’s rich malacological library and collections remain in the DBL. The dry collection is, at the time of writing, still in the order arranged by him and is of importance. It contains a large proportion of his type materials and numerous other series of shells identified by him, which in total are a valuable adjunct to his published descriptions, which are sometimes rather brief.
Few people enjoy conditions of employment and domestic life such as enabled Georg Mandahl-Barth to follow so freely his varied interests. The good use he made of his time was obvious to those like myself who talked with him and appreciated his wide knowledge of molluscs and natural history in general. Sadly that has passed away with him, but we may still admire the tangible achievements of what he published and the thriving Danish Bilharziasis Laboratory.