Impacts of supplementation aquaculture on the genetic diversity of wild Ruditapes decussatus from northern Spain

Abstract

The European carpet shell Ruditapes decussatus is among the most important shellfish species cultured in estuaries and bays of the northern Iberian Peninsula. Increased demand and overfishing of native R. decussatus, as well as irregular yields due in part to pollution and urban sprawl, have led to overexploitation of the species and to the import of the non-indigenous R. philippinarum in the early 1980s. In recent years, supplementation aquaculture of R. decussatus (supportive breeding) has been implemented as a management tool to recover the exhausted native carpet shell populations in Asturias, northern Spain. In this study, taxonomic analysis and a suite of genetic markers (ITS2, 5SrDNA, and mtCOI) were employed to assess the genetic composition of R. decussatus in 2 estuaries of the region, Ría del Eo and Ría de Villaviciosa. Our results revealed species misidentification and evidenced genetic introgression from the non-indigenous R. philippinarum into wild R. decussatus samples (4.2%), as well as in the aquaculture seed used for population supplementation (2.0%). Furthermore, we found significant genetic differentiation (F ST = 0.03750, p < 0.0001) between wild populations and aquaculture seed, while the adults of both estuaries were genetically homogeneous (p > 0.05). Several actions are strongly recommended to prevent inadvertent introduction of non-indigenous genomes and other genetic erosive processes on native species in the region: (1) banning releases of the alien species R. philippinarum, (2) developing diagnostic tests for detection of hybrids in captive breeding programs, and (3) assessing the conservation status of wild R. decussatus populations.

Morphological and Molecular Differences Between the Invasive BivalveRuditapes philippinarum(Adams & Reeve, 1850) and the Native SpeciesRuditapes decussatus(Linnaeus, 1758) from the Northeastern Adriatic Sea

“…Hybridization between the two species also imposes identification problems. For example, the introgressed genetic marker was found in individual specimens of apparent morphologically pure phenotypes, whereas individual specimens with intermediate morphology were genetically determined to be a pure species (Habtemariam et al 2015). Genetic analyses confirmed that the aforementioned morphological and morphometric characteristics can be soundly applied to differentiate between Ruditapes philippinarum and Ruditapes decussatus.…”

“…Hybrids between the allochthonous R. philippinarum and the autochthonous R. decussatus have been found in the north west and north of Spain (Hurtado et al 2011, Habtemariam et al 2015. As hybridization might lead to the local extinction of R. decussatus in areas where R. philippinarum is intentionally introduced to enhance commercial harvesting, Habtemariam et al (2015) suggested prohibiting the release of the alien R. philippinarum into natural waters as well as selecting non-hybridized R. decussatus for repopulation of overexploited areas. Hybridization between the two species also imposes identification problems.…”

Assessing the geographic scale of genetic population management with microsatellites and introns in the clam Ruditapes decussatus

“…; Habtemariam et al. ). However, only two studies have sampled a significant number of populations (Borsa et al.…”

Population genetics of the Manila clam (Ruditapes philippinarum) introduced in North America and Europe

“…The syndrome of ecological problems caused by invasive species is emerging in places where the Manila clam has established. This include an increase of clam numbers and the displacement of native species162326272829, but also, in Europe, hybridization with the native clam R. decussatus and subsequent introgression3031.…”