First record of niche overlap of native European plaice (Pleuronectes platessa) and non-indigenous European flounder (Platichthys flesus) on nursery grounds in Iceland.

Fifteen non-indigenous species have been recorded in Icelandic waters over the past decades, of which six have been classified as invasive or potentially invasive. One of these potentially invasive species is the European flounder (Platichthys flesus). Platichthys flesus is a recent arrival that was firstly identified in 1999 and has, since then, established a population around the whole country. In this study we evaluated if there is niche overlap between juvenile P. flesus and native juvenile European plaice (Pleuronectes platessa) on nursery grounds at three sites in west Iceland. Considering the presumed clockwise spread of P. flesus' population around the country, the southernmost site, Borgarfjörður, was treated as the site of earlier settlement of P. flesus. Similarly, the northernmost site, Önundarfjörður, was treated as the site of later settlement. We used stomach content and stable isotope analyses to examine if there was a significant niche overlap between P. flesus and P. platessa and to examine if the extent of niche overlap varied between sites. Multiple cohorts of P. flesus and native P. platessa were present at all sites and there was high niche overlap between species with no indication of trophic niche segregation nor change with time from establishment of P. flesus. The current study has shown the cooccurrence and niche overlap of non-indigenous P. flesus and native P. platessa on nursery grounds in Iceland and highlighted the establishment of P. flesus in Iceland as a rare case study to investigate colonisation processes of non-indigenous fish species in sub-arctic marine environments. [ABSTRACT FROM AUTHOR]