Biochemical composition of seston in two upwelling sites within the Humboldt Current System (21°S to 23°S): Summer conditions

The biochemical composition of seston within the Humboldt Current System (HCS) in two bays off northern Chile (21 degrees S-23 degrees 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 (-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. (C) 2010 Elsevier B.V. All rights reserved.