The diel characteristics of nitrate and ammonium uptake in a Gonyaulax polyedra bloom were observed during a field program along the west coast of Baja California. The simultaneous presence of light and inorganic nitrogen (especially nitrate) appeared necessary to generate uptake rates sufficiently high to allow growth of these dinoflagellate populations to bloom proportions. Field data from this and other areas revealed no significant differences in the light requirements of diatoms and dinoflagellates.
The seasonal onset of coastal upwelling off Baja California was studied during March 1972. Time series of stations were taken for 2 weeks at 27"N off Punta San Hipolito; data on physical, chemical, and biological variables are used to estimate the source of upwelled water, the rate of nutrient input to the euphotic zone, and the rate of subsequent biological utilization.Red tide dinoflagellates were observed to be a precursor of the presumably more typical diatom community of this upwelling ecosystem. This Gonyaulux polyedra dominated system suggests that these organisms lead to a longer food chain than that found later in the upwelling season. Pleuroncodes planipes, a facultative herbivore, was observed in large numbers but did not appear to be phytophagous during the transition from an oceanic to an upwelling food chain.Early expeditions to upwelling regions of the eastern boundary currents (Gunther 1936; Defant 1936 Defant , 1937 Sverdrup 1938) provided static intraseasonal descriptions of these systems. More recent studies have stressed the interseasonal repeatability of their structure (Jones 1972; Maeda and Kishimoto 197@), although the variability and the less predictable intensity of these phenomena are still not well known. Hypotheses have been advanced, for example, to implicate yearly changes in upwelling intensity as one of the factors involving species replacement within these ecosystems. A combination of heavy fishing pressure on sardines and increased upwelling of
Nitrate reduetase (NR) activity was assayed by measuring the ~qADtt-dependent formation of nitrite in phytoplankton extracts. NI~ specific activity increased with the nitrate concentration of the water in upwelling areas of the Peru Current. The temperature optimum for NI~ for natural phytoplankton was 15 ~ to 20 ~ NR activity showed diel periodicity, with maximum activity about noon and minimum activity near midnight local time. Rate of nitrate reduction in the extracts averaged only about i5 % of the rate of nitrate assimilation in the whole cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.