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The Winter-Spring Diatom Flowering in Narragansett Bay

David M. Pratt
Limnology and Oceanography
Vol. 10, No. 2 (Apr., 1965), pp. 173-184
Stable URL: http://www.jstor.org/stable/2833122
Page Count: 12
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The Winter-Spring Diatom Flowering in Narragansett Bay
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Abstract

Weekly observations of phosphate, nitrate, silicate, and phytoplankton over a 4 1/2-year period are analyzed to explain year-to-year variations in the time of inception and magnitude of the winter-spring diatom flowering in Narragansett Bay, Rhode Island. The population during this period (November-June) is dominated by Skeletonema costatum. The start of growth does not appear to be related to stability, temperature, or incident radiation; Martin (1965) has shown that it is triggered by the release of zooplankton grazing pressure. The diatom maximum is independent of temperature and incident radiation, and it is regulated by the concentrations of nitrate and silicate at the beginning of logarithmic growth, which also influences the magnitude of that part of the flowering that follows the winter maximum. In most years, considerable growth takes place after the exhaustion of nitrate, whereas growth was never observed to continue after silicate depletion. The relative importance and interplay of silicate and nitrogen as limiting factors are discussed. Since the flowering is greater the earlier it begins, its success is to some degree predetermined by zooplankton activity in the fall.

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