In the nutrient-rich offshore areas of the eastern tropical Pacific Ocean, chlorophyll levels were 4-10 times lower than might be expected if all the inorganic nitrogen had been assimilated. Three hypotheses are examined to explain this anomaly: 1) nitrate may be upwelled faster than it is assimilated; 2) the algae may be grazed to lower levels by herbivores; and 3) minor nutrients other than nitrate, phosphate, or silicic acid may be limiting....