Strategies for the retention of high genetic variability in European flat oyster (Ostrea edulis) restoration programmes

Abstract

The native European flat oyster Ostrea edulis is listed in the OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic (species and habitat protection) and in the UK Biodiversity Action Plan. Once extremely abundant in the nineteenth century, European stocks of O. edulis have declined during the twentieth century to rare, small, localised populations due to overexploitation, habitat degradation and, most recently, the parasitic disease bonamiosis. Selective breeding programmes for resistance to bonamiosis have been initiated in France and Ireland. High genetic diversity and bonamiosis-resistance would be important features of any sustainable restoration programmes for O. edulis. Oysters were sampled across Europe from four hatchery sources, four pond-cultured sources and four wild, but managed fisheries and were genotyped at five microsatellite loci. Hatchery-produced populations from small numbers of broodstock showed a significant loss of genetic diversity relative to wild populations and pedigree reconstruction revealed that they were each composed of a single large full-sib family and several small full-sib families. This extremely low effective population size highlights the variance in reproductive success among the potential breeders. Pond-cultured oysters were intermediate in genetic diversity and effective population size between hatchery and wild populations. Controlled hatchery production allows the development of bonamiosis-resistant strains, but at the expense of genetic diversity. Large scale pond culture on the other hand can provide a good level of genetic diversity. A mixture of these two approaches is required to ensure a healthy and sustainable restoration programme for O. edulis in Europe.

Stock enhancement or sea ranching? Insights from monitoring the genetic diversity, relatedness and effective population size in a seeded great scallop population (Pecten maximus)

“…This likely maximizes parental contributions in he resulting progenies. However, F ST and G-test results indicated a high genetic differentiation between wild and hatchery populations, as previously reported in other mollusks such as, the European flat oyster (Lallias et al, 2010a) and abalone (Hara and Sekino, 2007). This differentiation reflects a strong alteration of allelic frequencies in the hatchery that is most likely due to genetic drift resulting from the limited size of the broodstock (commonly 30-60 individuals), combined with high variance in reproductive success (Boudry et al, 2002;Morvezen et al, 2013).…”

“…This suggests that the genetic diversity of hatchery seed was not reduced much compared with the recipient wild population, contrary to what is often observed in hatchery production of bivalves (Taris et al, 2007;Lind et al, 2009;Lallias et al, 2010a). This might result from the care taken by the Tinduff hatchery in their crossing procedure (F Breton, personal communication): the great scallop being a simultaneous hermaphrodite, most individuals are commonly used both as male and female and batches of mixed spermatozoa from five to six individuals are used to individually fertilize ovocytes from each female.…”

The selection of an ideal diet for Ostrea edulis (L.) broodstock conditioning (part B)

“…In Europe, particularly France and Spain, O. edulis remains an emblematic species and attempts to develop "resistant strains" have been made in both countries (Lallias et al, 2010;Montes et al, 2003;Naciri-Graven et al, 1988). Moreover, such interest in flat oyster cultivation is now increasing in France due to high C. gigas juvenile mortalities (Pernet et al, 2010;Samain and Mc Combie, 2008).…”

The ecology, evolution, impacts and management of host–parasite interactions of marine molluscs

“…Coen and Luckenbach, 2000;Baggett et al, 2015;Coen and Humphries, in press). As interest in protection and restoration of shellfish habitats grows around the world (e.g., Laing et al, 2006;Coen et al, 2007;Beck et al, 2009Beck et al, , 2011Lallias et al, 2010;Woolmer et al, 2011, see http://www.oyster-restoration.org/oyster-restoration-research-reports/ also, last accessed 30 May 2015), it is important to understand how disease impacts the structure and function of these valuable habitats, and how restoration projects can be designed to enhance disease resilience in instances where it is hampering recovery (Coen and Luckenbach, 2000).…”