Deep-Sea Research, Vol. 26A, pp. 731 to 741 0011-7471/79/0701-0731 $02.00,/0 ,~ Pergamon Press Lid 1979. Printed in Great Britain Phytoplankton response to low level nutrient enrichment through upwelling in the Columbian Caribbean Basin JORGE E. CORREDOR* (Received 22 March 1978 ~ in revised form 11 December 1978; accepted 5 January 1979) Abstract -Inorganic nutrient enrichment through upwelling in the eastern Colombian Caribbean Basin stimulates phytoplankton growth. Growth rates, however,are significantly lower than those observed in the upwellingecosystems in the major eastern boundary currents becauseof the relatively impoverished nature of the source waters for the Guajira upwelling: the Subtropical Underwater. Initial organic growth factor limitation appears to cause uncoupling of nitrate uptake and phytoplankton biomass increase. Nitrate levels in recently upwelled waters are rapidly reduced to concentrations close to half-saturation constants previouslyreported for marine phytoplankton. INTRODUCTION PHYTOPLANKTON growth rates in marine ecosystems are closely regulated by inorganic nutrient availability. The work of THOMAS (1969, 1970a, b), DUGDALE (1967), and DUGDALE and GOERING (1967) indicates that, in stratified tropical marine waters, nitrogen is perhaps the single most important element limiting phytoplankton growth. WALSH (1977) has postulated that inorganic nutrient enrichment by vertical transport of subsurface waters is such that the concentrations of these elements are not significantly limiting for phytoplankton growth in upwelling areas within the major eastern boundary currents. BARBER, DUGDALE, MACISAAC and SMrTH (1971) presented evidence that other factors such as initial limitation due to lack of organic growth factors may be of greater importance in the dynamics of phytoplankton growth in these areas. Upwelling has been reported in the southern Caribbean Sea along the coast of Venezuela by numerous authors. MARGALEE (1971) reviewed the literature on biological aspects of this ecosystem. The upwelling along the Guajira Peninsula in the Colombian Caribbean Basin, (Fig. 1) has received little attention. GORDON (1967), PERLOTH (1971) and FAJARDO (1975) documented selected physical aspects of the upwelling. CORREDOR (1977) discussed some features of the phytoplankton populations in the area. The objective of this paper is to provide a comprehensive view of the rote of inorganic nutrient and organic growth factor limitation in the dynamics of phytoplankton growth in this ecosystem. The results of a 33-h drogue experiment are discussed in the light of current understanding of phytoplankton response to nutrient enrichment. Observations from this experiment are supplemented with historical data on nutrient distribution in the area. METHODS During cruise GS7504 of the University of Miami R/V James M. Gillis, a parachute drogue was released in a region of. active upwelling and followed for a total of 33 h. The * Rosenstiel School of Marine and Atmospheric Science,University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, U.S.A. Present address: Department of Marine Sciences, Universityof Puerto Rico, Mayaguez 00708, Puerto Rico. 73l