Surveying seaweeds from the Ulvales and Fucales in the world’s most frequently used artificial waterway, the Kiel Canal

Abstract

Abstract The Kiel Canal is one of the world’s most frequently used inland waterways and connects the SW Baltic Sea with the Wadden Sea. At the same time, the canal is a highly eutrophicated environment that is characterized by salinities that range from 3 to 16. This brackish character could make the Kiel Canal an important stepping stone for the introductions of species into the inner Baltic Sea. It could also hinder the identification of native and introduced species, given the fact that salinity sometimes severely affects algal morphology. Here we report on a survey of introduced and native seaweed species in the canal, focusing on the dominant groups, which are Fucales and Ulvales. Of the Fucales, the introduced species Fucus evanescens was detected nearly exclusively inside the canal, while Fucus vesiculosus dominated rockweed communities directly outside the sluice gates. Morphological analysis and genetic barcoding distinguished three species of Ulvales, Ulva linza, Ulva intestinalis and an unknown and possibly introduced species of the genus Blidingia. Species distributions and – in the case of U. intestinalis – branching patterns were clearly affected by salinity, while thallus sizes appeared to be affected by the specific eutrophication status of sites within the canal.