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

• Published in: Hydrobiologia 2001-06, Vol.453-454 (1), p.143-151
• Main Authors: Escribano, Ruben, Marin, Victor H, Hidalgo, Pamela
• Format: Article
• Language: English
• Subjects: Biomass; Calanus chilensis; Chile, Antofagasta, Mejillones Peninsula; Coastal zone; Copepoda; Upwelling; Vertical distribution; Zooplankton
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1013120005384

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^sup -3^, compared to ca. 5 ind. m^sup -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 10.4 km d^sup -1^ within the upwelling plume. This yielded a loss of biomass of 9.7 mg dry weight m^sup -2^ . Production, estimated by a temperature-dependent approach, ranged between 44 and 35 mg dry weight m^sup -2^ d^sup -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.[PUBLICATION ABSTRACT]