Succession of land snails (Gastropoda) in the Finnish Archipelago Sea

Authors

• Irene Routio University of Turku
• Matti Valta

Abstract

The Finnish southwestern archipelago, or the Archipelago Sea, consists of 40 000 skerries and islands, so more than in any other archipelago in Europe. Four species of land snails (Gastropoda) were found on skerries sized 100 to 500 m², seven species were found in the group of 500 to 1 000 m² -sized skerries, 21 were found on isles of 3 to 10 hectares, and 33 species were found on islands of 400 to 1 040 hectares. In total, 9 722 individuals from 36 different species were found. The smallest skerry from which land snails were found had an area of 298 m² and only one species, Oxyloma elegans.

The occurrence of Fucus vesiculosus algae walls in islands is an important regulating factor for land snails in the Finnish archipelago. Dead algae-matter is brought to shore by waves. Tall, long, decomposing walls of F. vesiculosus form an important microhabitat for land snails. Bird skerries are not a favorable environment for land snails due to the small amount of soil available and its high usage and consumption by birds. The height of the island is not a primary factor in the lives of land snails.

Species specialized and adapted to the harsh conditions of the archipelago are Oxyloma elegans, Pupilla muscorum and Balea perversa. Even small skerries have occurrences of Clausilia bidentata and Cochlicopa lubrica. Oxyloma elegans was observed following r-strategy for reproduction. No endemic species were found. A peculiarity was Cochlicopa lubrica’s black form repentina.