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The amount of food eaten by copepods of three genera (estimated from chlorophyll and pheophytin in the guts of the animals) was measured to determine the depth and also the time of day of the maximum and minimum intensity of feeding. Copepods were taken with a large volume (800 liters .min-') pumping system at five depths (O-85 m) and twelve sampling intervals (every 4 h) at three stations in the Peruvian upwelling system. Results indicate that Euculnnus could withstand periods of 12 h in anoxic layers, but Cnlanus and Centropages tended to be found in waters having more than 0.8 and 0.2 ml O,.liter-', that in situ filtration rates could be derived which were in accord with filtration rates obtained from laboratory studies, that individuals of the three genera migrated in and out of the 5-m surface layer when food was abundant but did not show a coherent diurnal vertical migration when food was scarce, and that the three genera maintained different feeding strategies which were amplified when food was scarce. The results are consistent with the concepts of resource allocation and separation of niches by species.

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Continuous estimates were obtained of zooplankton abundance, chlorophyll fluorescence, and water temperature along 10-to 100-kilometer transects of the North Sea. Spectral analysis methods were applied to the data. The "patchiness" of the plankton was distributed over all the length scales resolved with no indication of a characteristic patch size. The relative intensity of the zooplankton patchiness was greater than that of the phytoplankton at all spatial scales, with this difference becoming progressively greater for finer-scale features. In the North Sea data, the concentrations of phytoplankton and zooplankton consistently showed negative spatial correlations.

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