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

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. As a result of aquaculture activities Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded the European Wadden Sea. Using a variable noncoding mitochondrial marker, we show that the invaded range is the result of two independent invasions. Haplotype frequencies point towards two separate groups, one in the southern and the other in the northern Wadden Sea. We found virtually no genetic differentiation throughout the southern range and the putative source from British Columbia, Canada, suggesting that the Southern region can be considered as a closed population. In the North, mismatch distributions, haplotype ordination and isolation-by-distance analysis suggest a stronger, persistent impact of aquaculture on invasive populations. Due to the ongoing supply of new genetic material from hatchery production the northern invasive populations can therefore be considered as an open population highlighting the importance of aquaculture practice on the genetics of this keystone invader in the Wadden Sea.

New insights about the introduction of the Portuguese oyster,Crassostrea angulata, into the North East Atlantic from Asia based on a highly polymorphic mitochondrial region

“…For example, it is documented that C. angulata was introduced into Morocco from Spain and Portugal in 1952(Shafee 1985cited in Fabioux et al 2002. In contrast to C. gigas in Europe, which showed a typical star-shaped haplotype phylodiversity characteristic of expanding populations (Moehler et al 2011;Lallias et al 2015), the haplotype network of C. angulata did not show such a pronounced star-shape. Significant negative Tajima's D values were only found for C. angulata samples from Asia, although Fu's F tests were significant for Mira and Keelung samples.…”

“…The nucleotide divergence among C. angulata MNR haplotypes ranged from 0.2 to 1.9%. The nucleotide divergence between C. angulata and C. gigas MNR haplotypes (haplotypes identified by Moehler et al 2011 with the accession numbers JF505202-JF505277 and position 10615 to 11253 bp of EU672831) ranged from 8.2 to 10.2%. Table 1 shows the number of C. angulata haplotypes detected at each site.…”

“…The nucleotide diversity of C. angulata observed in the present study was higher than that previously reported for C. gigas for the same mitochondrial region. Moehler et al (2011) and Lallias et al (2015) reported nucleotide diversity values of 0.0044 and 0.0046 for C. gigas, respectively, with samples mainly collected in Europe but also in Canada and Japan. Hsiao et al (2016) found haplotype and nucleotide diversities (using mitochondrial cytochrome oxidase I sequences) in Asia being considerably higher in C. angulata than in C. gigas.…”

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

“…This species originates from East Asia and was imported for commercial cultivation worldwide (Arakawa 1990;Troost 2010), where it often spread from aquaculture facilities into the wild. Pacific oysters were also introduced from British Columbia to the Netherlands (1960s Dutch Delta;1980s Southern Wadden Sea;Drinkwaard 1999;Troost 2010) and from the UK to Germany (1990s northern Wadden Sea; Reise 1998; Moehler et al 2011). Currently, both of these genetically differentiated invasions (Moehler et al 2011) established persistent populations in the Wadden Sea (Ruesink et al 2005), raising conservation concerns over competition with native blue mussels (Mytilus edulis; Troost 2010).…”

“…Pacific oysters were also introduced from British Columbia to the Netherlands (1960s Dutch Delta;1980s Southern Wadden Sea;Drinkwaard 1999;Troost 2010) and from the UK to Germany (1990s northern Wadden Sea; Reise 1998; Moehler et al 2011). Currently, both of these genetically differentiated invasions (Moehler et al 2011) established persistent populations in the Wadden Sea (Ruesink et al 2005), raising conservation concerns over competition with native blue mussels (Mytilus edulis; Troost 2010). Together with the Pacific oyster, the parasitic copepod Mytilicola orientalis was co-introduced to Europe in the 1960/70 s via oyster imports from cultures in British Columbia (His 1977), where it had been introduced in the 1930s (then still known as Mytilicola ostreae ;Wilson 1938).…”