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Volume 38- Number 1 - 2003
Article


Daily fluctuation of phytoplankton in the upper layer of the ocean during the spring of 1997 in the north of Chile (20º18’S): II. Specific composition and cellular abundance

E. Santander, L. Herrera & C. Merino

 

Universidad Arturo Prat, Departamento de Ciencias del Mar, Casilla 121, Iquique, Chile

 

E-mail: esantan@cec.unap.cl

 

The response of the microphytoplanktonic community to the physical and chemical changes during an upwelling event is analyzed on a daily scale. The study coincided with the “El Niño” 1997-1998 presence, but the results did not show the anomalous condition associated with this event. The Upwelling Index values allowed us to divide the study period in two phases, the first one, from August 26 to September 7, when the events magnitudes were about 1,000 m3s-1, and the second from September 9 through 17, when the values were higher than 2,000 m3s-1. The microphytoplanktonic community structure was strongly coupled with the physical and chemical fluctuations caused by the variability of the upwelling events. During the first phase, Thalassiosira subtilis (Ostenfeld) Gran emend. Hasle was absolutely dominant, contributing 82.8% to the total cellular abundance, resulting in a community with a monospecific character. The decline and disappearance of T. subtilis was related to a change in the oceanographic conditions of the superficial layer, produced by the change in the upwelling intensity. In the second phase, the diversity increased in direct relation to a change in the specific composition of the microphytoplanktonic community, which led to Detonula pumila and Leptocylindrus danicus dominance. Salinity was the variable that significantly affected the observed community structure.


Key words: Daily variability, upwelling, diatoms, Pacific Ocean


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1Laboratorio de Zooplancton, Instituto de Ciencias del Mar y Limnología,Universidad Nacional Autónoma de México. A. P. 70-305, 04510 México, D. F. México
 
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