Spatial connectivity pattern of expanding gilthead seabream populations and its interactions with aquaculture sites: a combined population genetic and physical modelling approach

Abstract

In gilthead seabream the number of domesticated individuals increased annually, and escape events occur regularly in the Adriatic Sea. Still there is a lack of population genetic characteristics and evidence of the extent and geographic scale of interbreeding resulting from fish-farm escapees. We screened 1586 individuals using a panel of 21 neutral microsatellite loci in several consecutive years and here report on the medium-scale detection of hybrid and farmed seabream in the natural environment. Wild adults showed a lack of genetic structure within basin and sampling years and reduced connectivity with wild offspring collection, suggesting their temporal residency within the Adriatic. On the contrary, by linking the results of multiannual genetic analyses with the results of coupled hydrodynamic and individual based models (IBM-Ichthyop), we observed a strong connection of wild seabream associated with tuna-aquaculture sites and offspring from the nursery grounds, indicating that the surroundings of tuna sea-cage farms can function as a spawning grounds. The study results present the genetic baseline of wild and farmed strains from the eastern Adriatic Sea, as a first step toward development of a mitigation strategy for fish escapees aimed at controlling further erosion of genetic integrity.

Assignment of Gilthead Seabream Sparus aurata to Its Origin through Scale Shape and Microchemistry Composition: Management Implications for Aquaculture Escapees

“…Recent studies have shown that scale shape can be used as a good discriminator between congeneric species [27], sympatric phenotypes [28], populations [29] or geographic variants [30]. Here, we explored morphological and microchemistry patterns of gilthead seabream scales from different population origins, i.e., wild, wild farm-associated and farmed, sampled over a relatively small spatial scale that were previously characterized genetically and morphologically (whole-body shape) [6,8]. Based on the results presented above, multiple lines of inference are reported herein.…”

“…The gilthead sea bream, Sparus aurata, is an important demersal species in the aquaculture and fisheries sector throughout the Mediterranean. In recent years, increased numbers of wild gilthead seabream have been observed in the Adriatic Sea, and it has been suggested that rapid expansion of sea-cage farming, with the escape of fish from sea-cages and the positive effect of ocean warming on larval survival, have contributed to population increases for this subtropical species [5,6]. Several recent studies have confirmed that Adriatic tuna farms are areas of permanent residency of highly abundant wild seabream [7,8].…”

“…Such an altered environment has triggered the temporarily stable adaptation of both morphological and physiological traits, where wild farm-associated populations show a different head profile, body shape and enhanced reproductive fitness in comparison to those of wild or farmed fish origin [8]. Further on, at a very small spatial scale (<4000 km 2 ), these populations showed genetic differentiation with wild populations not associated with aquaculture sites, when 19 microsatellite loci were employed to investigate gilthead seabream population structure in the eastern Adriatic [6]. Such gene flow discontinuity observed between the wild farm-associated and wild fish collections was surprising given the long pelagic larval duration, up to 50 days at 17-18 • C, which is likely to contribute to the exchange of migrants among populations [9].…”

“…Thus, we employed three different approaches, i.e., landmark-and outline-based scale morphometrics, trace element chemistry profiles, and scale microstructure characteristics to test three hypotheses: (i) different environmental pressures can promote population differentiations over small geographical areas, (ii) scale shape has the same discrimination power as body shape of the same fish (from Talijančić et al [8]), and (iii) different methodologies may enhance the reliability and applicability of the data for monitoring and fisheries management. Scales were sourced from population origins with a known genetic background [6]. These populations were categorized as being of farmed, wild farm-associated or wild origin, and inhabited a variety of environments, i.e., human-mediated and natural ones.…”

Genome-wide analysis clarifies the population genetic structure of wild Gilthead Sea Bream (Sparus aurata)

“…Previous studies of the natural genetic structuring along sea bream distribution range did not provide a consistent scenario, and while some surveys report an absence of genetic differentiation among basins [18], others reported subtle genetic structure or population subdivision even at small geographical scale [19][20][21][22]; also, it cannot be excluded that aquaculture practices, also those involving other species (e.g. tunas or shellfish) have an effect in shaping the population genetic structure of the species [23]. Anyhow, these studies were mainly based on markers (e.g.…”