Ruben Escribano

Evolution and biological effects of the 1997–98 El Niño in the upwelling ecosystem off northern Chile

During the1997-98 El Ni~no event, the tempera- ture and oxygen contents of the coastal waters o northern Chile were noticeably higher than during non-El Ni~no con- ditions, butphytoplanktonandzooplanktonbiomasses were not dramatically altered. In contrast, the herbivorous cope- pod Calanus chilensis, which showed a limited tolerance to low-oxygenconditions,exhibitedgreaterabundances,higher growth rates, and a signicant reduction in adult body size. These results indicate a positive eect of the changes in oceanographic conditions due to El Ni~no on zooplankton growth and production, and provide evidence for lack of food limitation on secondary production in the coastal re- gion during this period.

Spatial distribution of copepods in the north of the Humboldt Current region off Chile during coastal upwelling

During the austral spring (December 1996), numerical abundance of copepod species (Crustacea: Copepoda) was estimated from 53 sampling stations scattered over the coastal waters off Mejillones Peninsula, northern Chile. Samples were obtained from two depth strata; 0-50 m and 50-200 m depth. Oceanographic data over the three-day cruise indicated that coastal upwelling was actively occurring during the survey. A total of 19 species was identified, of which four of them, Paracalanus parvus, Oncaea conifera, Oithona similis and Calanus chilensis, accounted for more than 80% of the whole copepod assemblage in terms of numerical abundance. Using the K-means exploratory analysis the 53 locations were grouped into two clusters: an upwelling type and a non-upwelling type. The former characterized by locations nearshore, with low temperature ( 13.4 mg m -3 ), while the latter had warmer waters (>18°C) and low chlorophyll-a (< 4.8 mg m -3 ). Chlorophyll-a (chl-a), distance to shoreline and temperature at 10m depth (T10) were all significant variables (P<0.05) for clustering analysis. There was a strong negative correlation between T10 and chl-a (P<0.01). The same clustering technique, based on species abundance, suggested the presence of a unique cluster, whose composition was dominated by P. parvus, O. similis, Acartia tonsa and Centropages brachiatus. Stepwise multiple regression showed that these species were also strongly correlated to chl-a and T10. Altogether these analyses suggest that water mass circulation during upwelling is the driving force for structuring spatial patterns of copepod distribution. In addition, a vertical distribution parameter suggested that copepods, independently of time of the day, tended to remain in a large proportion in near surface waters, possibly constrained by a shallow oxygen minimum layer. This implies that advection during active upwelling may cause large fractions of populations being transported offshore, allowing zooplankton export to more oceanic waters. Rapid turnover rates of copepods growing continuously year-round, may act as a mechanism to compensate population losses during persistent coastal upwelling.

Selective incorporation of bacteria by Argopecten purpuratus larvae: implications for the use of probiotics in culturing systems of the Chilean scallop.

Abstract Experiments on ingestion rates, colonization and impact of inhibitory producer substances bacteria (IPB) on larvae of Argopecten purpuratus , were carried out to evaluate potential use of bacteria as probiotics in cultures of this Chilean scallop. Three selected strains, named as 11, C33 and 77, obtained from larval cultures of A. purpuratus were tested at different concentrations and incubation times. After 6 h of incubation at a concentration of 10 6 cells ml −1 , A. purpuratus larvae ingested cells of strains 11 and 77, but not those of C33. When comparing bacterial incorporation among these strains, the 77 became the dominant bacteria of the larval microflora, causing no differences in larval survival at different bacterial concentrations. Our results suggest that strain 77 appears as a potential probiotic for scallop larvae and hence, as a promising method to control and prevent infections in hatcheries systems.

Recording of ocean-climate changes during the last 2,000 years in a hypoxic marine environment off northern Chile (23°S)

Atmosphere-ocean interactions are particularly strong along the Chile-Peru coast and largely account for the extreme aridity of the Atacama Desert. Near the center of the driest part of this coastal desert, we found that the embayment Bahia Mejillones constitutes an unusually favorable setting for the formation and subsequent preservation of a sedimentary record of the successive oceanographic conditions of the last few thousand years. This work deals with relative abundance of various bio-indicators, including fish scales, foraminifers and phytoplankton, with a centimetre-scale resolution, in several gravity cores taken from 80 to 120 m depth, in a low-oxygen environment. We use this information to document oceanclimate changes at decadal to centennial time scales in the region. Radiocarbon dating on the bulk organic-rich sediment provides the chronological framework for the observed paleoceanographic changes. We interpret that an episode of relatively warmer water, with a stratified water column and enhanced anoxic ( 0.3 ml l -1

Temperature-dependent development and growth of Calanus chilensis Brodsky from Northern Chile

Abstract Development and growth of Calanus chilensis Brodsky were studied under laboratory conditions to establish the temperature-dependent rate function of embryonic development, to analyze potential maternal effects on development rates, and to study development and growth from egg to adult. As in previous studies, embryonic duration estimated at 9, 12, 15, 18 and 20°C, was described by the Bělehradek model of development and the fitted equation was D =947.7 ( T +11.0) −2.05 , where D is embryonic duration (days) and T is temperature (°C). The parameter values, a =947.7 and t 0 =11.0, were comparable to those published for C. marshallae . At a constant temperature of 15°C the embryonic duration depended on females, indicating a significant maternal effect and increasing variance within temperatures. When reared with excess of food at 15°C, individual copepodites grew exponentially, with a generation time of 38 days. The weight-specific growth rate was 0.114 day −1 , and changes in body length were linear through time. Our results show that temperature-dependent predictions of generation time, number of generations per year, and female body size are not consistent with field data, suggesting that food shortage during the annual cycle may retard development and affect adult body size. An untested alternative hypothesis involves the potential vertical migration and permanency of individuals in deep waters. Development under low temperatures would give rise to larger animals and to fewer generations a year, consistent with the temperature-dependent prediction.

Circulación inducida por el viento en Bahía de Antofagasta, norte de Chile (23° S)

Se estudio la circulacion de la bahia de Antofagasta (23° S) sobre las base de mediciones de series de tiempo de corrientes en verano e invierno de 1999, de un crucero oceanografico realizado en agosto de 1999 y una serie de 9 meses de perfiles de corrientes a intervalos de 15 dias. La informacion de corrientes sumada a datos de temperatura, salinidad y oxigeno, e informacion de vientos, permitio analizar la variabilidad temporal y espacial de la circulacion en la bahia. La bahia de Antofagasta esta sujeta a una intensa variacion de los vientos, a la cual las corrientes se manifiestan muy asociadas y en desfases de tiempo de 1 hasta 5 dias. El ciclo que presenta mayor contribucion a la varianza total de la corriente es en la escala diaria. La bahia presenta circulacion en una capa, con velocidades medias de 30 cm s-1. El campo de corrientes sugiere que la bahia se llena a traves del sector norte y su vaciamiento ocurre en el extremo sur. La presencia de un foco de surgencia en el sector sur externo a la bahia ejerce una fuerte influencia en la circulacion, a traves del influjo de aguas de surgencia desde el sur y dando origen a una zona frontal que modula el llenado y vaciado de la bahia. El estudio presenta un modelo conceptual de circulacion sujeta a la variabilidad en la intensidad de surgencia. El modelo predice que bajo condiciones de relajacion de surgencia y el establecimiento de zona frontal en la boca sur la circulacion seria dominada por un giro ciclonico al interior de la bahia, y frente a pulsos de intensificacion de la surgencia se produciria el llenado. Se discuten las implicancias de los resultados en el contexto de la capacidad de retencion y renovacion de aguas de la bahia.

The influence of coastal upwelling on the distribution of Calanus chilensis in the Mejillones Peninsula (northern Chile): implications for its population dynamics

A field experiment was carried out in October 1998 during active upwelling in a coastal area off the Mejillones Peninsula (23°S). Zooplankton was sampled at day and night, during two subsequent days at 4 stations inside and outside of the upwelling plume. Three depth strata were sampled: 0–20 m, 20–80 m and 80–200 m. Oceanographic data were obtained in a grid of 23 stations using a CTDO, a fluorometer and a Doppler current meter. Calanus chilensis was mostly represented by late stages, i.e. copepodid C5 and adult males and females. There were no day/night effects on vertical distribution, and abundance was significantly higher inside the upwelling plume in the upper 20-m layer at nearly 14 ind. m−3, compared to ca. 5 ind. m−3 outside the upwelling plume. Temperature at 10 m depth and biomass, estimated from stage numbers and their mean dry weights, were used to estimate growth and daily production of Calanus at temperature-dependent rates. The potential loss of biomass from the upwelling center because of advection in the upwelling plume was estimated from current data in the Ekman layer and biomass density. The mean cross-shelf component of the current was estimated at 10.4km d−1 within the upwelling plume. This yielded a loss of biomass of 9.7 mg dry weight m−2. Production, estimated by a temperature-dependent approach, ranged between 44 and 35 mg dry weight m−2 d−1, at mean temperatures of 14.6°C and 15.8°C inside and outside of the upwelling plume respectively. Within the plume, as much as 22% of daily production may be advected offshore. However, a higher concentration of biomass in the upwelling plume allowed a greater production compared to surrounding areas. A mass balance approach suggests that advective losses may not have a major impact on the C. chilensis population, because of very high daily production at temperature-dependent rates.

Succession of pelagic copepod species in coastal waters off northern Chile: the influence of the 1997–98 El Niño

A 2-year time series (∼ 17-d interval) of zooplankton, sampled from June 1996 through January 1998, along with oceanographic data, allowed the study of species abundances and diversity during non-El Nino and El Nino conditions at Mejillones (23° S) northern Chile. A total of 28 species was identified, of which the most abundant were the calanoids Paracalanus parvus, Calanus chilensis, Acartia tonsa, and Centropages brachiatus, the cyclopoid Oithona similis, and the poecilostomatoids Oncaea conifera and Corycaeus typicus. El Nino Southern Oscillation (El Nino) was first detected in the area in May 1997 and persisted until March 1998. We divided the time series into two parts: non-El Nino conditions. The number of species significantly increased during Eland El Nino conditions, but total abundance of copepods was greater during non-El Nino conditions. Although some expatriate species appeared during El Nino, such as the harpacticoid Microsetella norvegica and Eucalanus subtenuis, the diversity index of Hulburt was not significantly different between the two periods. Despite the dramatic alteration of oceanographic conditions during the El Nino period, we concluded that the community of pelagic copepods was not subject to drastic changes either in total abundance or in structure.

Distribución de eufáusidos en el sistema de surgencia frente a la península de Mejillones (23°S) asociada a condiciones previas y durante El Niño 1997-98

Euphausiids are abundant, although little studied components of the zooplancton in the Humboldt Current ecosystem. For instance, the effect that large scale ocean variability may exert on their population dynamics, abundance and distribution is unknown. In this work, based on 2-year time series data and two spatial surveys on December 1996 and July 1997, the distribution of euphausiids in coastal zone off Mejillones Peninsula was assessed. 10 species were identified, of which the most abundant were Euphausia mucronata, E. distinguenda and a non-identified species of the genus Euphausia. In July 1997 (El Nino conditions) fewer species were observed as compared to December 1996 (prior to the El Nino). In both situations (prior and during the El Nino) the abundance of various species was associated with surface dissolved oxygen and water density. There was no correlation between euphausiids abundance and phytoplankton biomass. Previous to the El Nino 1997-98 a Diel Vertical Migration (DVM) pattern was observed for most species, with greater abundance in the upper 0-50 m layer at night. Under the El Nino conditions DVM was apparently altered by intrusion of the warm water mass. E. mucronata, E. distinguenda, Euphausia sp. and Nematoscelis megalops, were found during the time series study. The abundance of adults of these species was significantly reduced during the warm conditions of the El Nino. By contrast, juveniles and larvae (furcilia and calyptopis), not identified to the species level, were significantly more abundant during the El Nino phase, suggesting that reproduction was continuous throughout the study and even incremented during the El Nino. During the warm conditions of the El Nino we also observed a decrease in body length of adults, juveniles and larvae. When comparing equal months in both periods (El Nino and non-El Nino), the body lengths of juveniles, larvae and at least for one species in adults, were significantly smaller during the El Nino period.

Life cycle of Calanus chilensis Brodsky in Bay of San Jorge, Antofagasta, Chile

The copepod Calanus chilensis is an endemic component of the zooplankton community in northern Chile. Size distributions of adult females, relative frequency of copepodid stages and relative numbers of adult males and nauplii, suggest the presence of at least 6 generations during the year, although the species seems to continuously reproduce through all seasons. Temperature profiles from 0 to 175 m indicated the presence of the ‘El Nino’ current during March and April. Surface temperature ranged between 21.1 and 13.1 °C. Warm waters during the ‘El Nino’ event seemed to affect the body size of adult females and the normal course of cohort development, although the population tended to recover rapidly through the subsequent months. We discuss the role of oceanographic conditions in controlling the life cycle of this species, as well as its continuous growth through the year compared to other Calanus species.