Flounder growth and production as indicators of the nursery value of marsh habitats in a Mediterranean lagoon

Estuarine marshes are known as suitable nursery areas for many marine migrant fishes, such as flounder. The potential nursery value of such habitats was investigated in the Venice lagoon, by using growth and production of 0-group flounder as indicators. Size-frequency distribution analysis was performed on fish samples collected fortnightly, from March 2004 to June 2005, in two marsh sites, Dese and Tessera, differing in their origin and environmental conditions. Samples were mostly composed of juvenile individuals, belonging to 0- and 1-group cohorts (the latter being present in Tessera only). A higher total production, either annual or monthly, and faster growth of 0-group flounder was observed in Dese, associated to a higher ecological performance of 0-group individuals in this site, as indicated by the higher P:B ratio values. Dese is a site located in a marsh complex characterized by the relevant influence of a nearby river, and the observed higher potential nursery value of this marsh area with respect to the other is discussed in the light of the higher trophic status and other environmental conditions in this site. The production results were also compared to those from other estuarine environments commonly acknowledged as important nurseries for European flounder.