Biochemical composition of seston in two upwelling sites within the Humboldt Current System (21°S to 23°S): Summer conditions Enrique Isla a, ⁎, Patricia Homs a , Elisabet Sañé a , Rubén Escribano b , Gabriel Claramunt c , Nuria Teixidó d a Institut de Ciències del Mar-CSIC, Passeig Marítim de la Barceloneta 37-49, 08003, Barcelona, Spain b Center for Oceanographic Research in the Eastern South Pacific (COPAS), Departamento de Oceanografía, Universidad de Concepción, Chile c Universidad Arturo Prat, Departamento de Ciencias del Mar, Iquique, Chile d Centre d'Estudis Avançats de Blanes-CSIC, Accés a la Cala St. Francesc 14, 17003, Blanes, Spain abstract article info Article history: Received 28 July 2009 Received in revised form 17 March 2010 Accepted 20 March 2010 Available online 28 March 2010 Keywords: Seston Biogenic silica Humboldt Current System Upwelling Lipids Proteins The biochemical composition of seston within the Humboldt Current System (HCS) in two bays off northern Chile (21°S–23°S) was assessed to estimate its chemical quality as potential food supply for benthic communities, large zooplankton and fish larvae. As part of the CENSOR project, in the summer of 2006 physical and biochemical variables were analyzed in Chipana and Mejillones Bays during one week at four depths determined by the occurrence of the upper boundary of the oxygen minimum zone and fluorescence peaks. The depth of the oxy- and pycnoclines controlled the distribution of biochemical variables in both bays. There were significant differences in the concentration of protein (PRT), lipid (LPD) and carbohydrates (CHO) among depths in both bays. The differences were also found in the PRT and LPD contribution to the biopolymeric carbon (BPC) among bays and among depths in the case of CHO. However, the concentration of suspended particulate matter and biogenic silica (bSi) were similar in both bays. PRT, LPD and CHO showed the highest concentrations in the upper meters of the water column and small peaks close to the seabed related to sediment resuspension and/or lateral transport. In Chipana Bay, the high nutritive quality of seston occurring near the seabed suggests a rapid sinking of diatom aggregates and a reduced respiration of the particulate organic matter. PRT, LPD and CHO varied between 0.05 and 0.47 mg l -1 , 0.06 and 0.39 mg l -1 and 0.07 and 0.51 mg l -1 , respectively. LPD were the most important contributors to the BPC in both bays. The seston in these bays presented a high PRT and LPD content in comparison to a number of settings of different latitudes and oceanographic characteristics. The high quantity and biochemical quality of the particulate matter in both bays may reflect the high productivity of this zone and partially explain their condition as spawning areas within the HCS. © 2010 Elsevier B.V. All rights reserved. 1. Introduction High primary productivity regions, such as upwelling zones, sustain abundant marine communities feeding on suspended partic- ulate matter or seston that presents high nutritive quality (Copin- Montegut and Copin-Montegut, 1983; Graf, 1992; Gago et al., 2003; Lee et al, 2006). Among these regions, the Humboldt Current System (HCS) extending from approximately 5°S (Peru) to 37°S (Chile) in the Eastern Pacific(Sobarzo and Figueroa, 2001) is considered one of the most productive areas of the ocean, providing almost 15% of the 80 million tones of the estimated global fisheries (Hill et al., 1998). This high production is mostly sustained by the fertilizing effect of wind-driven coastal upwelling, which pumps nutrients into the euphotic zone over the continental shelf (Barber and Smith, 1981). The HCS is subject to strong interannual variability due to the El Niño- Southern Oscillation (ENSO) (Escribano et al., 2004). ENSO changes the “normal” seasonal regime of the spring–summer benthic hypoxia to a higher oxygenation near the bottom. This causes an increase in benthic macrofauna biomass and bioturbation of sediments in association with the disappearance of filamentous bacterial mats (Escribano et al., 2004). In spite of the bio-economical importance of this area, the region located south of 15°S is still poorly investigated (Fonseca, 1989; Shaffer et al., 1995). The need for understanding the factors and mechanisms that determine its high biological productiv- ity and the strong oceanographic and social effects caused by El Niño events in the region (Fuenzalida, 1985; Blanco and Díaz, 1985; Kelly and Blanco, 1986; Fuenzalida, 1992) has motivated the development of new studies such as the international CENSOR project (Climate variability and El Niño Southern Oscillation: implications for natural coastal Resources and management; www.censor.name). Within this frame, the present study aims to assess the characteristics of seston in highly productive, upwelling areas through the analysis of the quantity and quality of the suspended particles as potential food supply for benthic communities, large zooplankton and fish larvae. Journal of Marine Systems 82 (2010) 61–71 ⁎ Corresponding author. E-mail address: isla@icm.csic.es (E. Isla). 0924-7963/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2010.03.004 Contents lists available at ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys