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Secondary production of copepods is one of the basic parameters that govern the structure and function of the marine pelagic food web, and it is commonly estimated as cumulative biomass increase through consecutive molting based on short-term molting rate (MR) incubation experiments. The accuracy of the method depends on two underlying assumptions: (1) Even stage duration and inter-molt growth; (2) All copepods in situ are alive. We conducted a year-long study in a coastal bay within the Humboldt Current System to assess the errors in copepod secondary production estimation when these assumptions are violated. Abundances of live and dead individuals of the dominant species: Paracalanus cf. indicus, Acartia tonsa and Calanus chilensis were measured monthly. Concurrent molting rate experiments were conducted to derive copepod secondary production. A modified MR formulation was used to correct the secondary production estimates for error in assumption (1), and the live/dead copepod data were used to correct the estimates for error in assumption (2). Violation of the underlying assumptions caused error in secondary production estimation, most severely in P. cf. indicus. The error was not evenly distributed across the months, and in the case of C. chilensis, it switched between over-and underestimation repeatedly. The annual average error was-39.2% in P. cf. indicus, 3.1% in A. tonsa, and 5.2% in C. chilensis. The errors also varied in magnitude and in sign among developmental stages, with some stages yielding nearly 70% over-estimation. For copepod species with short generation times, even small errors could quickly propagate and result in highly skewed secondary production projection. Reliable secondary production measurements therefore require careful assessment of species-specific stage duration and betweenstage growth when applying the MR method, and quantification of stage-specific live and dead individuals in the field.

Morphological changes in the exoskeleton of naupliar stages 2-6 and copepodid stages I-V of Rhincalanus nasutus are described. On the distal segment of nauphar antennule, one lateral seta and two medial setae are added during each molt to nauplius 3-6. A naupliar arthrite is a thick, distinctive structure on the coxa of antenna, and the exopod of this limb is patterned from the large proximal segment of that ramus. The coxal gnathobase of the mandible appears at nauplius 4. Buds of maxillule and maxilla are added during the molt to nauplius 5, and buds of maxilhped and sviiimming legs 1-2 are added during the molt to nauplius 6. The somite bearing maxilla clearly articulates completely with the somite bearing the maxilhped on the last two naupliar stages. This unusual articulation does not appear during copepodid development, and the somite bearing swimming leg 2 is the anterior articulating somite during this later phase. One articulating somite is added during molts to copepodid 11-V. Segmentation of the antennule is completed by copepodid IV. Segmentation of the exopod of antenna does not change during the copepodid phase, but one segment is added to the endopod of maxilla. Segmentation and setation of the maxilhped follow the usual calanoid pattern. Buds of swimming legs 3-5 are ventrolateral on their somite. Their presumptive exopod has two attenuations; their presumptive endopod bears an attenuation and a seta. Segmentation of the rami of swimming legs 1-4 follows the common pattern for copepods except for the exopod and endopod of swimming leg 1 which are only 2-segmented.PAMELA HIDALGO ET AL. RESUMENCambios morfológicos en el exoesqueleto de estadios naupliares 2-6 y estadios copepoditos de Rhincalanus nasutus son descritos. El segmento distal de la anténula naupliar, muestra que una seta lateral y dos setas intermedias son adicionadas durante cada muda desde el naupUus 3 al nauplius 6. El artrito naupliar presenta una gruesa estructura distintiva sobre la coxa de la antena y el exopodito está marcado desde el mayor segmento proximal de esta rama. La gnatobase de la coxa de la mandíbula aparece en el nauplius 4. Inicios de la maxilula y maxilla aparecen durante la muda hacia el nauplius 5, e inicios del maxilipedo y los apéndices natatorios 1 y 2 aparecen durante la muda del nauplius 5 al nauplius 6. El somito presenta la maxila claramente y completamente articulada y el maxilipedo aparece en los dos últimos estadios naupliares. Esta inusual articulación no aparece durante el desarrollo de copepoditos y el somito presenta la pata nadadora 2 en la articulación anterior en esta fase. Articulaciones del somito aparecen durante las mudas de copepodito II a copepodito V. La segmentación de la antenula es completada en el copepodito IV. La segmentación del exopodito de la antena no cambia durante la fase de copepodito, pero un segmento es adicionado en el endopodito de la maxila. La segmentación y setación de los maxilipedos sigue el normal patrón de calanoideos. Los crecimientos de las patas natatorias 3-5 se ...