The occurrence of egg-cocoons of the leech Piscicola geometra (L.) in recent lake sediments and their relationship with remains of submerged macrophytes

Abstract

The leech Piscicola geometra (L.), a widespread European ectoparasite on freshwater fish, deposits characteristic egg-cocoons on submerged macrophytes as well as on stones and shells. The present paper explores the use of sedimentary P. geometra cocoons as a palaeolimnological indicator of the presence of submerged macrophytes. In a study of recent sediments of seven Danish eutrophied lakes that have undergone declines in submerged macrophyte cover, the stratigraphical record of P. geometra cocoons was found generally to parallel that of the remains of submerged macrophytes. Although no P. geometra cocoons were recorded in the sediments of one of the seven lakes, more than 95 % of sediment samples with cocoons also had remains of submerged macrophytes. Cocoon concentrations in excess of 5 per 100 cm 3 fresh sediment were almost invariably associated with remains of submerged macrophytes. Cell imprints from the phorophyte on the ventral side of the cocoons can be used to verify their association to plant macrophytes. It is suggested that, in a wide area in northern Central Europe, egg-cocoons of P. geometra may be used as a simple palaeolimnological indicator of the earlier presence of submerged macrophytes in lakes with medium to high alkalinity.