Seasonal mesoscale shifts of demersal nekton assemblages in the subtropical South-western Atlantic

Abstract

ABSTRACTThe present study shows a hitherto undocumented pattern of mesoscale seasonal shifts of teleost fish and cephalopod assemblages along the shelf and upper slope of southern Brazil. Through multivariate techniques we discerned four consistent groups: coastal, warm shelf, cold shelf and upper-slope assemblages. The warm shelf and the upper-slope assemblages were present year round, whereas the cold shelf assemblage occurred almost exclusively in the cold season, and the coastal assemblage expanded toward the south in the warm season. The coastal and shelf nekton fauna was dominated by juveniles and adults of the sciaenid fishes Macrodon ancylodon, Cynoscion guatucupa, Micropogonias furnieri, Umbrina canosai and Paralonchurus brasiliensis, the cutlassfish Trichiurus lepturus and the hake Merluccius hubbsi. The upper-slope assemblage was more diversified and included Polyprion americanus, Urophycis mystacea, the squid Illex argentinus and macrourids. Similar to other subtropical Atlantic ecosystems, the dominance of sciaenids is related to the large areas of sand and mud bottoms, and the low salinity due to the high freshwater runoff of the La Plata River and Patos Lagoon. The choice of seasonal or spatial closures or the planning of marine protected areas may benefit from a greater understanding of the seasonal spatial shifts of the fish assemblages.