Biological Oceanography of the 



Eastern Tropical Pacific: Summary 



of Existing Information 



By 



MAURICE BLACKBURN, Research Biologist 



Institute of Marine Resources, Scripps Institution of Oceanography 



University of California, San Diego 



La Jolla, California 92037 



ABSTRACT 



Investigations of the biological oceanography of the eastern tropical Pacific 

 are reviewed. Published papers, papers in press, and completed manuscripts, 

 are briefly summarized. On most of the 29 biological-oceanographic expeditions 

 made since 1 952, similar properties were measured by similar methods. Numbers of 

 available comparable measurements are: standing crop of surface chlorophyll a_, 

 1,153; surface primary productivity, 603; standing crop of small zooplankton in the 

 upper 300 m., 875; standing crops of chlorophyll a and micronekton in the upper 

 100 m., about 100 each; other types of measurements, small numbers. 



The measurements of surface chlorophyll a, surface productivity, and zoo- 

 plankton are analyzed by 14 areas which are distinguished on the basis of the 

 physical structure of the upper 200 m. and by half-yearly periods irrespective of 

 year. The analysis by areas shows that all three measurements are highest in up- 

 welling areas (coastal and equatorial) and areas with thin mixed layers, lowest in 

 areas with thick mixed layers (in the subtropical anticyclonic current gyrals), and 

 intermediate elsewhere. The analysis by periods is partly inconclusive because of 

 the uneven distribution of observations through the year. The most interesting result 

 is the unexpected lack of statistically significant differences between property means 

 for the 2 half-years in some of the areas which are believed (on physical-ocea- 

 nographic grounds) to be seasonally eutrophic. 



The paper also summarizes findings reported elsewhere on changes in bio- 

 logical properties with depth and time of day and on successive days. Past studies 

 on statistical relationships between different properties measured at the same times 

 and places and on the ecology of special groups of organisms (especially chaetog- 

 naths, considered as possible "indicators" of water masses or property-distribu- 

 tions) are also summarized briefly. Numerous deficiencies of knowledge are evi- 

 dent; increased research could contribute fundamentally to the much neglected study 

 of biological oceanography in the tropical oceans of the world. 



INTRODUCTION where. The purpose is to state the principal 



biological-oceanographic results obtained 



This paper is a summary of biological from the region in ways that may suggest 



oceanography of the eastern tropical Pacific needs for further work and the forms it should 



Ocean. It is mainly a review of published take. The emphasis is placed on modern meas - 



papers and completed manuscripts , most of urements of properties of the kind that are 



which were written by others, but it includes of general interest and may be made anywhere 



some material which has not appeared else- in the ocean and on ways in which the data 



