Grazing of Pseudocalanus Minutus on Naturally Occurring Particulate Matter

The quantity and size of particulate matter consumed by Pseudocalanus minutus were studied in seawater samples collected from different depths and from closely spaced stations. The heterogeneity in particle distribution resulted from quantitative and qualitative fluctuations in the particle spectrum, although at times the total concentration was about the same. Pseudocalanus minutus consumed particles between 4 and 100 µ. An electivity index value was more often positive for 25.4–57.0‐µ particles. On the average, particles <39 µ were more readily eaten than larger particles. The consumption by copepods at different locations was related not only to particle concentration but also to the pattern of the particle size spectrum. Pseudocalanus was able to shift its grazing pressure from small to large particles to compensate for a reduction in density of small particles.