Feeding ecology of the invasive Cynoscion regalis on the Portuguese coast: Insights from a molecular approach

Invasive species can profoundly disrupt native ecosystems, as their self-sustaining populations alter niche occupation, increase competition, and exert predation pressure on indigenous species. Predation by invasive species, particularly on vulnerable life stages such as larvae and juveniles, can lead to population declines, loss of genetic diversity, disruption of food webs, extinction of keystone species, impaired ecosystem services, and delayed recovery of indigenous populations. Cynoscion regalis (Bloch and Schneider, 1801), commonly known as the weakfish, is a sciaenid species native to the eastern coast of North America, where it acts as a generalist predator. Since 2009, its presence has also been documented in European waters, prompting concerns about its potential impact on local fish communities. This study presents the first molecular analysis of the feeding ecology of C. regalis outside its native range. Using molecular barcoding of prey items coupled with metabarcoding of gastric fluids, this research provides insights into the weakfish’s diet in Portuguese waters (southwestern Europe) beyond those obtained in studies relying solely on visual stomach content identification. This underscores the value of molecular techniques in dietary analysis. Findings reveal that C. regalis exhibits cannibalistic tendencies, with conspecifics forming a substantial part of its diet. Other dietary species include Atherina presbyter , Diplodus annularis , Dicentrarchus punctatus , Engraulis encrasicolus , Sardina pilchardus , and Spondyliosoma cantharus . In addition, other prey were identified at the family level as Sparidae and Scorpaenidae. The presence of these species, many of which are common in estuarine habitats, particularly during juvenile stages, supports the establishment of weakfish populations in nursery areas, potentially resulting in adverse ecological impacts. This study contributes to understanding the dynamics of invasive species, highlighting the ecological interactions and disturbances they may cause. Effective monitoring and management of weakfish populations outside their native range are critical to mitigating potential ecological consequences.Parte superior do formulário