Matching an Old Marine Paradigm: Limitless Connectivity in a Deep-Water Fish over a Large Distance

SIMPLE SUMMARY: The response of marine fish species to external pressures highly depends on their intrinsic bio-ecological traits. Among those species of commercial interest, the deep-water Blackspot Seabream (Pagellus bogaraveo, Brünnich 1768) inhabits a large geographical range, a condition that might contribute to high resilience to fishing activity. The biology of the species has been patchily investigated in past years, and to date a complete picture of its connectivity across its distribution area (Eastern Atlantic Ocean and Mediterranean Sea) has not been available. We investigated the species’ genetic variability and differentiation at a very large geographical scale by analysing nuclear DNA markers. The absence of genetic population structuring over such a wide area was found, strengthening the hypothesis that egg and larval dispersal are fundamental in sustaining the genetic connectivity of the Blackspot Seabream. ABSTRACT: Investigations of population structuring in wild species are fundamental to complete the bigger picture defining their ecological and biological roles in the marine realm, to estimate their recovery capacity triggered by human disturbance and implement more efficient management strategies for fishery resources. The Blackspot Seabream (Pagellus bogaraveo, Brünnich 1768) is a commercially valuable deep-water fish highly exploited over past decades. Considering its exploitation status, deepening the knowledge of intraspecific variability, genetic diversity, and differentiation using high-performing molecular markers is considered an important step for a more effective stock assessment and fishery management. With one of the largest efforts conceived of and completed by countries overlooking the Atlantic and Mediterranean coasts in recent years, a total of 320 individuals were collected from different fishing grounds in the Mediterranean Sea and Atlantic Ocean and analysed using 29 microsatellite loci. We applied multiple statistical approaches to investigate the species’ connectivity and population structure across most of its described distribution area. Considering the incomplete knowledge regarding the migratory behaviour of adults, here we suggest the importance of egg and larval dispersal in sustaining the observed genetic connectivity on such a large geographical scale.