Feeding ecology of juvenile flounder Platichthys flesus in an estuarine nursery habitat: Influence of prey-predator interactions

The present study aimed to investigate the feeding ecology and influence of prey-predator interactions on juvenile flounder Platichthys flesus in an Atlantic estuarine nursery area (Lima estuary, NW Portugal), focusing on prey selection and ontogenetic shifts in the diet. The relationship between prey availability and flounder distribution was also investigated. Juvenile flounder diet included 21 taxa of macroinvertebrates and fishes, sand and plant debris. According to numerical, occurrence, and gravimetric dietary indices, macroinvertebrates, namely Chironomidae and Corophium spp. were the main prey items. The diet diversity tended to increase as juveniles grew, although some dietary overlap occurred between the early juveniles (50-149 mm total length (TL)). In fact, the diet diversity of the newly settled juveniles (< 50 mm TL) was particularly low, evidencing the importance of Chironomidae. Moreover, an ontogenetic shift was evident, since older juveniles (1+) presented a distinct diet, including new items absent from the diet of the 0+ juveniles, namely Teleostei, Carcinus maenas, and Nemertea. The juvenile flounder presented an overall generalist behavior, feeding on the most abundant macroinvertebrates namely Chironomidae and Corophium spp., as evidenced by the Strauss linear index. The spatial distribution of the 0+ flounder in the Lima estuary was associated with salinity and prey (Chironomidae and Corophium spp.). These preys were characteristic of the upper estuary where most of the juveniles, especially the newly settled, were found. Hence, this study reinforces the importance of both abiotic and biotic factors as environmental driven controls of habitat use during the early phases of the demersal life of European flounder.