Alien parasitic copepods in mussels and oysters of the Wadden Sea

Abstract

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 cointroduced 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.

Spillover but no spillback of two invasive parasitic copepods from invasive Pacific oysters (Crassostrea gigas) to native bivalve hosts

“…Species identity of all individuals was morphologically ascertained under a stereo microscope (magnification 10-309) by using the shape of the dorsal appendages as main differential character (pointy in the introduced M. orientalis and blunt in the established M. intestinalis ;Gotto 2004;Elsner et al 2011).…”

“…), subsamples from both parasite species were also molecularly identified with a diagnostic RFLP (restriction fragment length polymorphism) assay developed from taxon specific primers based on Elsner et al (2011; see Online Resource 5 for details). During the main sampling in May, 921 adult Mytilicola were recovered from Pacific oysters and blue Spillover but no spillback of two invasive parasitic copepods 369 mussels.…”

“…This intestinal parasite has a direct life cycle with a free-living larval stage and was originally described by Mori (1935) from Pacific oysters in its native range in the Sea of Japan. In the Dutch Delta, M. orientalis has been observed since the 1990s (Stock 1993), whereas it has only recently been documented in the Wadden Sea (Elsner et al 2011;Pogoda et al 2012). The parasite was reported to show relatively low host specificity (Lauckner 1983;Grizel 1985) and has already spilled over to M. edulis and Ostrea edulis at European (French and Dutch) coasts (His 1977;Stock 1993).…”

Nonnative macrobenthos in the Wadden Sea ecosystem

“…The American razor clam Ensis (directus) americanus presumably arrived with ballast water released in the German Bight in front of the Wadden Sea or near the western Dutch Wadden Sea (Wolff, 2005). The mussel parasite Mytilicola intestinalis and the eel parasite A. crassus were first encountered near the Elbe estuary in the central Wadden Sea (Elsner et al, 2011;Koops and Hartmann, 1989). Three other species were first found in the former Zuiderzee which was an embayment of the Wadden Sea until its conversion into land and a freshwater reservoir since 1932 (Wolff, 2005).…”

Invasion genetics of Pacific oyster Crassostrea gigas shaped by aquaculture stocking practices

“…Owing to high late summer temperatures in the early 2000s a strong expansion could be observed reaching population densities from 100 to 2000 individuals m − 2 (Nehls and Büttger, 2007;Nehring et al, 2009;Reise et al, 2005). Since wild C. gigas in the Wadden Sea is not commercially harvested, apparently not affected by predators, parasites and competitors to a large extent (Elsner et al, 2011;Kochmann et al, 2008;Krakau et al, 2006;Reise and van Beusekom, 2008), further population growth can be expected. This oyster invasion is perceived as the most severe impact an alien species so far had on the ecosystem of the Wadden Sea (Nehring et al, 2009), partly because mussel beds around low tide line became dominated by oysters with ecological consequences for native species (Diederich, 2005(Diederich, , 2006Markert et al, 2010;Troost, 2010).…”