Distribution of planktonic cnidarian sin response to South Atlantic Central Water intrusion in the South Brazilian Bight

Abstract

Five oceanographic cruises were made between November200 5andJune 2006, sampling across-shelf transect off the South Brazilian Bight (SBB;261460S) to follow the seasonal development the South Atlantic Central Water(SACW) intrusion over the shelf and its influence on the assemblage of planktonic cnidarians. An on shore wind-driven bottom intrusion not the SACW was clearly perceptible, reaching the coast in January. From March onward, the SACW influence was gradually displaced seaward duet owind and tidal mixing. By late June the SACW influence was offshore and theinshore was dominated by low-salinity waters (o34.5). The abundance, distribution, and general taxonomic composition of both medusae and Siphonophores were strongly influenced by the onshore intrusion of the SACW. An inshore–offshore gradient was clear. The Canonical Correspondence Analysis suggested that coastal species – dominated by Liriope tetraphylla, actinul a larvae and Muggiaea kochi – were mostly related to food availability and a vertically mixed environment inshore ,and their abundance and extent were reduced during periods. In contrast , species with offshore affinities tended to increase their abundance and distribution during intrusion periods, and were mostly related to the presence of thermal stratification and a deep chlorophyllmaximumlayer.Mostoftheseoffshorespecies,suchas Aglaura hemistoma, Rhopalonema velatum and manycalycophorans, areassociated with the war mupper layer. However, high concentration soff large (420 mm indiameter) Solmaris corona were observed exclusively in cold waters, suggesting this medusa is a SACW indicator