Consideraciones sobre la hidrografia y el zooplancton del puerto de Castellón : San Feliu Lozano, J., 1962. Inv. Pesq., Barcelona, 21: 3–27.

Abstract

The nearshore region of central Chile is important for spawning of sardine (Sardinops sagax) anchovy (Engraulis ringens) and jack mackerel (Trachurus murphyii) and the importance of fisheries for these species has led to an interest in factors controlling the area's productivity. We studied daily variations in productivity at a nearshore station (25m depth) off Dichato, Chile (36°30′S) during January 1986 to understand how wind-driven variability in the hydrography is translated into pulses of primary and secondary production of the plankton. During the study period, we observed three complete cycles of upwelling favourable/unfavourable winds. Water column destratification, as indicated by the surface-to-bottom gradient of sigma-t, lagged the wind by about one day. During active upwelling, cold water (<11.5°C) of high nitrate and low oxygen concentration (20–25μM and 1–2ml 1−1 respectively) was found near the surface. During subsequent relaxation of upwelling, the water column became stratified as temperature, oxygen and chlorophyll increased.The size and taxonomic composition of the phytoplankton varied from one event to the next. Over the course of the study, from 15–100% of the chlorophyll could pass a 20μm mesh screen. Chain-forming diatoms, microflagellates, and the autotrophic ciliate Mesodinium rubrum dominated the first, second and third events, respectively. In rank order of abundance, Paracalanus parvus, Centropages brachiatus, Oithona spp., Acartia tonsa, Oncaea spp., Calanoides patagoniensis and Calanus chilensis dominated the copepod community. Changes in abundance of most species did not closely follow the upwelling cycle. Possibly, vertical movements or other behavioural responses caused zooplankton distributions to be uncorrelated with movements of the surface Ekman layer. Fecundity of several of the important copepod species was measured using the egg ratio and bottle incubation techniques. Compared to values reported in the literature, egg production was usually suboptimal, despite high nutritional quality of the phytoplankton, as indicated by protein/carbohydrate ratios. Food availability, due to either small phytoplankton size or spatial and temporal uncoupling of phyto- and zooplankton populations, was probably most important in limiting copepod production.Event-scale advection, both zonal and alongshore, can be important in uncoupling primary and secondary production and probably determines the degree to which upwelling-generated pulses of phytoplankton production are utilized by herbivorous plankton in the nearshore zone.