Inaugural Conference - June 2002

MASS MORTALITY OF EIDER DUCKS IN THE WADDEN SEA:
WHAT IS THE ROLE OF PARASITES?

Fred Borgsteede, Pedro Zoun, Lelystad, The Netherlands; Anna Okulewicz, Jerzy Okulewicz, Wroclaw, Poland

During the last two winters, thousends of Common Eiders (Somateria mollissima) died in the Wadden Sea, the Netherlands. There has been an extensive debate about the cause of this mass mortality. Is it just a lack of food, or are parasites the cause? Macroscopic inspection of dead eiders revealed in most cases the presence of the acanthocephalan Profilicollis botulus. Because this helminth uses crabs (Carcinus maenas) as intermediate host, a theory was developed, that due to lack of their usual food (mussels, cockles), the eiders were forced to feed on crabs and therefore became infected with such quantities of parasites that they succumbed.
The aim of the present study was to investigate if this theory was right by doing a complete parasitological survey of ten eiders. The results of the most important parasite groups were as follows: (minimum and maximum numbers between brackets).
Acanthocephalans: P. botulus (50-4,000); Nematodes: Amidostomum acutum (50-800), Capillaria mergi (50-1700), two other nematode species in small numbers; Trematodes: present in all eider ducks, 18 different species with sometimes huge numbers (>30,000), the most frequent ones were Cryptocotyle concavum and several species belonging to the Fam. Microphallidae; Cestodes: also present in all eider ducks and also sometimes in huge numbers (>10,000), but most worms in not well developed form and therefore not suitable for species identification.
Particularly A. acutum is known as a very pathogenic parasite. The hypothesis from these results is that the heavy infection with the stomach worm A. acutum leads to inappetence, due to malfunctioning of the stomach. The final result is anorexia and death due to starvation.

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