Phytoplankton in an Oligotrophic Ocean: Observations and Questions

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Abstract
Details of the vertical distribution of oceanic phytoplankton species are investigated by means of four stations occupied during June 1977 and August 1978 near 28°N, 155°W. Two distinct, recurring floral associations, separated by a region of rapid transition near or below 100 m, are identified. The associations are apparently related to the "nutrient limited" and "light limited" physiological regimes described previously. Inverse abundance relationships of congeners within the deeper association are compatible with the hypothesis of disequilibrium competitive interactions and community regulation. Among species of the shallow association congeners are positively associated and predation is postulated to be the important regulating mechanism.