Plasticity of European flounder life history patterns discloses alternatives to catadromy

Abstract

European flounder (Platychthys flesus) life history patterns were investigated at three locations along a latitudinal gradient (Minho- N-Portugal, Gironde- SW-France, Seine- N-France). We used coupled Sr:Ca and Ba:Ca otolith signatures and microstructure to retrospectively determine habitats occupied by flounder during early life history stages and spawning events. Our results showed a high diversity of life history patterns within each sampling location and between locations. Egg signatures showed two distinct origins, coastal or freshwater, suggesting that flounders may use two different spawning habitats. The coastal type egg signature was dominant at all locations, and the freshwater egg signature was most frequent in the Seine. During pre-metamorphosis, the predominant habitat for flounder larvae varied between all sites. The freshwater habitat was the predominant habitat for the Seine’s pre-metamorphic and metamorphosed flounders (40%); while in the Gironde and in the Minho, the predominant habitats were the coast (52%) and the estuary (79%), respectively. The diversity of life history patterns was greatest in the Gironde (16), than in the Seine (12) or in the Minho (9). During the first year of life of the Seine’s flounder, most fish stayed in freshwater environments (40%). This pattern was the third most frequent for Gironde flounder (12%), but it was not observed in flounder captured in the Minho. Our study suggested that flounder use estuarine and coastal spawning grounds. Hence, catadromy in European flounder may be facultative behavior, and the species exhibits great plasticity in the life history patterns, which adaptative value still remains to be investigated.