Alien parasitic copepods in mussels and oysters of the Wadden Sea

Molluscan intestinal parasites of the genus Mytilicola, specifically M. intestinalis, were initially introduced into bivalves in the North Sea in the 1930s. It was presumably introduced from the Mediterranean with ship-fouling mussels, then attained epidemic proportions in Mytilus edulis in the 1950s and is now widely established in the North Sea region. Mytilicola orientalis was co-introduced with Pacific oysters to France in the 1970s and in the southern North Sea in the early 1990s. Its main host Crassostrea gigas has massively invaded the Wadden Sea with a concomitant decline in mussels. To explore whether introduced mytilicolid parasites could play a role in the shifting dominance from native mussels to invasive oysters, we analysed 390 mussels and 174 oysters collected around the island of Sylt in the northern Wadden Sea. We show that M. intestinalis has a prevalence > 90% and a mean intensity of 4 adult copepods in individual mussels with > 50 mm shell length at all sheltered sites. By contrast, none were found in the oysters. However, at one site, we found M. orientalis in C. gigas with a prevalence of 10% and an intensity of 2 per host individual (August 2008). This constitutes the most northern record in Europe for this Pacific parasite until now. Alignments of partial sequences of the mitochondrial cytochrome oxidase I (COI) gene and the nuclear internal transcribed spacers (ITS) and 18S rDNA sequences each show a distinct difference between the two species, which confirms our morphological identification. We suggest that the high parasite load in mussels compared to oysters may benefit the continued expansion of C. gigas in the Wadden Sea

Effects of Parasitic Crustacea on Hosts

This chapter summarises our understanding of the direct effects that parasiticcrustaceans have on their invertebrate and vertebrate hosts. At the individual hostlevel, the effects of infection with parasitic Crustacea with respect to host pathologicalchanges and the development of disease states are reasonably well understood. However,we have a much poorer understanding of how infection affects the physiological,immunological and reproductive status of hosts, with much of what is known arisingfrom studies of sea lice (caligid copepods) infections of salmonids. Quantifyingsublethal impacts of parasitic Crustacea infection on the biology and ecology of hostsis especially challenging even under controlled laboratory conditions. This is due to thecomplex and poorly understood interactions between parasite, host and environmentaldeterminants, which ultimately influence the outcome and magnitude of the effect.There is very limited information on the effects that parasitic Crustacea have on theirhosts at a population level, as well as on the indirect effects that they may have onspecies that interact with their hosts (community level effects). Our relatively goodunderstanding of effects of sea lice on salmonids has been brought about due to thelarge economic impact that these parasites have on farmed salmonids and the necessityto develop new methods for their control. Unfortunately, the progress for other parasitesand hosts is much slower which is in part due to the lack of experimental systems,research tools and funding