Parasite communities of the Schlei Fjord (Baltic coast of northern Germany)

Abstract

The parasite faunas of snails, mussels, crustaceans and small-sized fishes were investigated over a period of six months in the Schlei fjord, on the Baltic coast of Schleswig-Holstein. Two sites differing in salinities were compared: Missunde with 5–9 ‰ and Olpenitz with 12–20 ‰. Prevalences, number of host-parasite combinations, numbers of core and secondary species were generally higher in Olpenitz than in Missunde. In the latter site, only prevalences of cestodans in planktic copepods and the number of rare species were apparent. Specificity of parasites was relatively high in snails, mussels and fishes, but lower in benthic crustaceans. Parasites may survive in an extreme environment like brackish water by means of special strategies which differ from those acquired in the marine milieu: suspension of specificity, adaptation to hosts which are genuine brackish water species, extension of host spectra, and shortening of life-cycles. Although the parasite communities of the Schlei fjord were primarily influenced by the prevailing salinities, the influence of other factors, e.g. environmental stress, was also confirmed. Whereas generally low prevalences in Missunde may contradict Thienemann’s biocoenotic rule, planktic parasites infested their hosts often at higher rates than in Olpenitz. This phenomenon is explained by the poorer environmental condition of the benthal zone in Missunde compared to that of the pelagial or the benthal zones of Olpenitz.