Upper trophic structure in the Atlantic Patagonian shelf break as inferred from stable isotope analysis

The Patagonian Shelf is a very productive region with different ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and different coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatial-temporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average delta N-15 value of pelagic guild (Illex argentinus) was remarkable lower than those of the other guilds. The delta C-13 values of almost all species ranged from -17 parts per thousand to -18 parts per thousand, but Stromateus brasiliensis had a significant lower delta(13)C( )value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower delta N-15 values.