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The Role of Pelagic Crags in the Grazing of Phytoplankton Off Baja California

Alan R. Longhurst, Carl J. Lorenzen and William H. Thomas
Ecology
Vol. 48, No. 2 (Mar., 1967), pp. 190-200
Published by: Wiley
DOI: 10.2307/1933100
Stable URL: http://www.jstor.org/stable/1933100
Page Count: 11
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The Role of Pelagic Crags in the Grazing of Phytoplankton Off Baja California
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Abstract

The galathied crab Pleuronocodes planipes, which occurs in very dense and extensive pelagic concentrations to the west of Baja California, is capable of filter-feeding on natural diatom blooms. Its filtering mechanism is similar to that previously known in Porcellana. It is only in regions of coastal diatom blooms that Pleuroncodes feeds exclusively on Phytoplankton; elsewhere, it feeds on protista and zooplankters. A study of production and grazing in a coastal upwelling situation suggested that the observed zooplankton community would have incapable of sustaining more than about 10% of the apparent grazing rate, and calculations based on estimated grazing rates for Pleuroncodes suggested that the observed standing stock of this species could go far towards supplying the remainder of the apparent grazing pressure. Pelagic crabs may thus, at least in certain situations, play a dominant role in grazing down diatom blooms in the southern part of the California Current.

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