Parasites in the northern Wadden Sea: a conservative ecosystem component over 4 decades

Helgol Mar Res (2008) 62:3747 DOI 10.1007/s10152-007-0091-6

ORIGINAL PAPER

Parasites in the northern Wadden Sea: a conservative ecosystem component over 4 decades

David W. Thieltges Birgit Hussel Judith Hermann K. Thomas Jensen Manuela Krakau

Horst Taraschewski Karsten Reise

Received: 18 February 2007 / Revised: 14 August 2007 / Accepted: 18 October 2007 / Published online: 24 November 2007 Springer-Verlag and AWI 2007

Abstract We investigated potential changes in the meta-zoan endoparasite fauna in the northern Wadden Sea during the past 4 decades by compiling published studies, reports and original data. During the time considered, the parasite fauna has remained basically the same. Only a few changes in parasite species presence occurred that resulted from changes in host distribution and abundance. The introduction of potential host species had little eVect on the parasite community because no alien parasites were concomitantly introduced and the native parasites show low prevalence and intensity in these novel hosts. Eutrophication and eVects of phased-out hunting may not have had clear bottomup or topdown eVects on the parasite community because of various confounding factors. Parasites depending on several host species may only be subject to strong population changes if all hosts are aVected in a unidirectional way. This, however, is rather unlikely to happen in a coastal ecosystem subject to multiple pressures. Hence, parasites appear to be a relatively conservative component of the northern Wadden Sea.

Keywords Alien species Climate Trematodes ProWlicollis Mytilicola Invertebrates Birds Long-term Marine parasitism

Introduction

Endoparasites are an intrinsic but hidden part of coastal ecosystems (Sousa 1991; Mouritsen and Poulin 2002). They aVect host individuals, populations, and communities in various ways and thus alter food web structures and ecosystem functioning (Mouritsen and Poulin 2002, 2005; Thompson et al. 2005). In coastal invertebrates, the dominant metazoan parasite group are digenetic trematodes with complex life cycles (Fig. 1). First intermediate hosts are mostly gastropods in which the parasites multiply and cercariae develop. The free-living cercariae infect a second intermediate host, most often a bivalve, crustacean, or Wsh. When these hosts are consumed by a Wnal hostWsh, bird, or mammalthe cycle is completed. In the vertebrate hosts, the trematodes mate and produce eggs that infect the

Wrst intermediate invertebrate host. Birds play a dominant role as Wnal hosts in coastal ecosystems...