Seasonal patterns of cephalopod paralarvae distribution in relation to oceanographic features off South Brazil Bight (SBB)

Abstract

Event Abstract Back to Event Seasonal patterns of cephalopod paralarvae distribution in relation to oceanographic features off South Brazil Bight (SBB) Carolina C. Araújo1* and Maria D. Gasalla1 1 Instituto Oceanográfico, Brazil Cephalopods play an important role in marine food webs worldwide, supporting industrial and artisanal fisheries. However, the knowledge about early life stages of cephalopods and their mechanisms responsible for distribution, recruitment and variability in the South Brazil Bight (SBB) is still poorly understood. In SBB occurs waters from the mixing between Tropical Water (TW), warm and saline (T> 20 ° C and S> 36.40) transported in the surface layer of the Brazil Current (BC), the South Atlantic Central Water (SACW), relatively cold (T <20 ° C and S <36.4), transported CB in the lower layer, and the Coastal Water (CW), resulting from mixing continental freshwater discharge to the continental shelf, and the lower salinity (S <34) waters of the SBB. This area is influenced by local and remote winds, tides, baroclinic pressure gradients due to buoyancy advections and variability mesoscale of the BC. The BC produces a flow on the platform southward and away from the coast during the summer and a flow toward the north and the coast during the winter. Seasonal variability of BC causes a different behavior of water bodies, due to formation of vortices and eddies induced by changes in wind patterns. In summer, the Ekman transport generated by the dominance of northeast winds and training vortices in BC, moving surface water, promoting the intrusion and resurgence of SACW, which is rich in nutrients and responsible for the increase primary productivity. The penetration SACW during the summer stratification causes the formation of a strong thermocline, on the other hand, the water column becomes homogeneous during winter due to its retreat toward the slope. At Cabo Frio region where the continental shelf is narrowest the coastline direction changes from NE-SW to approximately E-W that favoring the upwelling phenomenon. Plankton samples obtained during the Project “Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul” (DEPROAS) from two surveys using bongo and multi plankton sample (MPS) nets, both with 333 µm mesh were examined in order to identify cephalopod paralarvae composition, distribution and abundance on fourteen transects perpendiculars from the coastline during summer (bongo: n=49; MPS: n=58) and winter (bongo: n=47; MPS: n=47) off SBB between Cabo de São Tomé and São Sebastião Island (22°-24°S) up to 200 m in relation to oceanographic features, such as water masses and mesoscale features. The samples were collected oblique (from near bottom to surface) and stratified (10 to 20 meters intervals) hauls at ~ 2 knots during 10 minutes. The mean water temperature for all the study area, from surface to 200 m depth, was significantly higher in the summer (~20.3°C) than in the winter (~20.3°C). During the summer the water column was strongly stratified, while during the winter the water column was relatively homogeneous. The T-S diagrams show the presence of three water masses in the area: Tropical Water (TW), South Atlantic Central Water (SACW) and Coastal Water (CW). The Tropical water mass occupied the layer between the surface and 100 m depth, mainly in the oceanic region. In the deep layer (> 100m depth) values below 18°C and salinity between 35 and 36 were registered, suggesting the presence of the SACW mass. The SACW was also found at the surface in the coastal region, Cabo Frio and indicating a coastal upwelling event. In the southern coastal area the temperature was about 20°C and salinity 34 during both summer and winter, indicating the presence of a CW mass. Overall 337 cephalopod paralarvae were identified representing seven families: Ancistrocheiridae (Ancistrocheirus sp), Argonautidae (Argonauta sp), Enoploteuthidae (Abralia sp and Abraliopsis sp), Loliginidae (Doryteuthis spp), Octopodidae (Octopus spp), Ommastrephidae (Illex sp, Stenoteuthis sp and Ommastrephes sp) and Sepiolidae (Heteroteuthis sp). A total of 199 (summer) and 68 (winter) of cephalopod paralarvae were collected with bongo net. During summer Argonautidae (Argonauta) was most frequent (44%) followed by Enoploteuthidae (18%), associated to stratified water columns formed with CW in the surface layers and SACW in deeper layers. During winter Octopodidae (Octopus) was most frequent (35,3%) followed by Enoploteuthidae (16,2%), associated to TW in the surface and SACW in deeper layers. Loliginidae paralarvae was found nearshore (until 100m isobath) associated to stratified water column formed by CW in surface layers and SACW in the deeper layers. Enoploteuthidae, Argonautidae and Ommastrephidae occurred mainly in the middle shelf (upper 100m isobath) related to waters masses (TW and SACW) transported by BC. A total of 50 (summer) and 20 (winter) of cephalopod paralarvae were collected by MPS net. Cephalopod paralarvae were most frequent until 40 m depth associated to thermocline. Enoploteuthidae was most frequent upper 20 m, indicating relation to warmer waters (TW) transported by BC. Overall, the density of cephalopod paralarvae correlates with oceanographic processes during summer when productivity is locally enhanced. The present study provides new information on cephalopods early life stage patterns in the area that will be useful to investigate recruitment patterns and fisheries assessment of cephalopods populations. Acknowledgements The authors are grateful to the responsible for the Biological Collection “Prof. E. F. Nonato” (Institute of Oceanography, University of São Paulo) for plankton samples. Keywords: cephalopods, paralarvae, Brazil Current, thermocline, distribution patterns Conference: XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016. Presentation Type: Oral Presentation Topic: 3. OCEANOGRAPHY, MODELLING AND ECOSYSTEM DYNAMICS Citation: Araújo CC and Gasalla MD (2016). Seasonal patterns of cephalopod paralarvae distribution in relation to oceanographic features off South Brazil Bight (SBB). Front. Mar. Sci. Conference Abstract: XIX Iberian Symposium on Marine Biology Studies. doi: 10.3389/conf.FMARS.2016.05.00088 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 May 2016; Published Online: 02 Sep 2016. * Correspondence: Ms. Carolina C Araújo, Instituto Oceanográfico, São Paulo, São Paulo, 05508-090, Brazil, carolcosta27@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. 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