Latitudinal trends in habitat quality of shallow-water flatfish nurseries

The habitat quality of European shallow-water nurseries was studied for 3 common flatfish species based on juvenile growth conditions. Field growth of 0-group plaice Pleuronectes platessa, flounder Platichthys flesus and sole Solea solea, from both published and unpublished studies, was compared with maximum growth predicted by a bioenergetics model based on the dynamic energy budget theory. In plaice and flounder, realized growth ratio decreased consistently during the growing season in most of the nurseries analyzed, indicating a widespread pattern of declining conditions. In sole, growth performance was not maximal, but as opposed to the other species, no clear temporal trend in realized growth ratio was observed. A latitudinal comparison of realized growth ratio over the various nurseries indicated clear positive trends for plaice and flounder, with better growth conditions at northern latitudes. In sole, despite some variability, the same trend was found during part of the summer. In the absence of clear gradients in benthic prey biomass, we hypothesize that increased food limitation in southern locations is most likely caused by interspecific competition reducing maximum individual intake rates. These results suggest that, in the context of global warming, habitat quality of southern European nurseries for juvenile growth may be particularly affected by the combined interaction of food and thermal constraints.