Coupling of life cycles of the copepods Calanus chilensis and Centropages brachiatus to upwelling induced variability in the central-southern region of Chile Pamela Hidalgo * , Ruben Escribano Departamento de Oceanografı ´a, Centro de Investigacio ´ n Oceanogra ´ fica en el Pacı ´fico Sur-Oriental (FONDAP-COPAS), Universidad de Concepcio ´ n, Estacio ´ n de Biologı ´a Marina, Casilla 42, Dichato, Chile Available online 2 September 2007 Abstract A time series of zooplankton sampling carried out at Station 18 off Concepcio ´n (36°S, 73°W) from August 2002 to December 2003 allowed the study of annual life cycles of the copepods Calanus chilensis and Centropages brachiatus in association with environmental variability in the coastal upwelling zone. Changes in the abundance of eggs, nauplii, and copepodids were assessed from samples taken at a mean time interval of ca. 20 days. Upwelling variability in near- surface waters was reflected in seasonal changes in salinity, water column stratification, and oxycline depth, as well as a weak seasonal signal in sea surface temperature (1–2 °C). Both copepods exhibited similar life cycles, characterized by con- tinuous reproduction throughout the year. Estimates of generation times, as a function of temperature, were 25–30 days for C. chilensis and 27–35 days for C. brachiatus, predicting about 12 and 10 generations a year, respectively. These esti- mates were consistent with reproduction pulses observed in the field. It was thus suggested that copepods may grow under non-limiting food conditions in this upwelling area. However, despite continuous reproduction, there were abrupt changes in population sizes along with the disappearance of early naupliar and copepodid stages taking place even during the upwelling season (spring/summer). These changes were attributed to sudden increases in mortality taking place in spring or early summer, after which the populations remained at low levels through the fall and winter. It is thus suggested that, in addition to variability in the physical environment, biological interactions modulating changes in copepod mortality should be considered for understanding copepod life cycles in highly productive upwelling systems. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Copepods; Life cycle; Generation time; Population dynamics; Upwelling Regional Index Terms: Pacific ocean; Humboldt current; Chilean coast 1. Introduction The population dynamics of pelagic copepods in the coastal zone off Chile seem to be strongly coupled to the upwelling process (Peterson et al., 1988; Escribano and Hidalgo, 2000a; Giraldo et al., 2002; Hidalgo et al., 0079-6611/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.pocean.2007.08.028 * Corresponding author. Tel.: +56 41 268 3247; fax: +56 41 268 3902. E-mail address: pahidalg@udec.cl (P. Hidalgo). Available online at www.sciencedirect.com Progress in Oceanography 75 (2007) 501–517 Progress in Oceanography www.elsevier.com/locate/pocean