Environmental drivers of the distribution of the order Pleuronectiformes in the Northern Spanish Shelf

A total of 17 species of the order Pleuronectiformes were caught in standardized groundfish surveys in the Cantabrian Sea and Galician waters between 2002 and 2011. The abundance and distribution of the dominant flatfish species were analysed, as well as drivers that affected the distribution. The results of a hierarchical classification analysis indicated three primary assemblages: (1) an inner shelf group (~ 50-100 m), characterized by Pegusa lascaris, Buglossidium luteum and Solea solea; (2) a medium and outer shelf group (~ 125-250 m), represented by Arnoglossus laterna, A. imperialis, Microchirus variegatus, Lepidorhombus whiffiagonis and L. boscii; and (3) a shelf break and upper slope group (~ 325-450 m), formed by Bathysolea profundicola. MANOVA analyses indicated that depth was the primary structuring factor, although sediment size and geographical position were also important. A bathymetric segregation pattern was drawn and indicated species replacement with increasing depth irrespective of size. Most of the species appeared to be associated with fine sand, except A. imperialis, which showed more association with coarse sand. The most abundant species were L. boscii, M. variegatus and A. laterna, which also had the widest and most ubiquitous distribution. They had a clear distribution farther west, whereas the rest seemed to be a more eastern group, and L. whiffiagonis, B. profundicola and A. imperialis were present at more northern latitudes. A. laterna was the most abundant species in the Galician shelf. In general, flatfish species in the northern Spanish shelf go through a slight ontogenetic niche shift primarily as a function of depth and sediment size. Smaller individuals tend to occur in shallower waters than their larger counterparts, except for A. laterna, M. variegatus and L. boscii, which have the opposite behaviour. Most flatfish show an affinity for a larger sand grain size with growth.