Quantitative investigations of the BalticFucusbelt macrofauna

Abstract

A remote operating device for obtaining quantitative samples of bushy algae is described. An algal plant, fixed in the middle of a collapsible cage is used as a natural trap. Lines operating from the sea surface ensure a rapid enclosure of the alga which after a week's exposure has received a natural fauna. The device has worked quite satisfactorily for a period of more than two years of continuous exposure with a monthly sampling of the Baltic fauna. An annual maximum of animals of around 600 specimens per 100 g dry Fucus occurs in November, dominated by the crustaceans Idatea and Gammarus and the molluscs Hydrobia, Theadaxus and Cardium. The annual minimum occurs in January with around 100 specimens. A more frequent sampling has shown that especially the molluscs and Gammarus invade the initially empty Fucus plant very rapidly.