The "Abyssal Society". François-Alphonse Forel and the Case of Deep Fauna in Late 19th Century.

Ichthyological investigations and technological advancements, such as the laying of submarine telegraph cables, promoted new dredging methods in the second half of the 19th century. In contrast to the idea of a lifeless deep ocean (Edward Forbes' azoic hypothesis), the discovery of deep water fauna and the challenge of defining its systematics opened up new theoretical perspectives. In this frame, which was already marked by the impact of Darwin's theory, naturalistic surveys in freshwater environments in western Switzerland intertwined with those of oceanographic expeditions. The study of the fauna in the depths of subalpine lakes by the Swiss savant François-Alphonse Forel was one of the most striking examples of this turning point, because the relatively recently evolution of its freshwater fauna allowed him to investigate: (a) the role of isolation, (b) the progressive differentiation of species from a common ancestor, and (c) the constitution of a species-specific category in form transition, from a genealogical viewpoint to an ecological one.