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The action of light and temperature on the activity of Simocephalus serrulatus (Koch) Alderdice, Donald Francis


Apparatus has been designed and developed for determining the response of the plankton Crustacean Simocephalus serrulatus (Koch) to horizontal gradients of light and temperature. These factors were varied independently or combined under standardized conditions. The temperature preferendum for this organism, cultured in a constant environment, was found to be 19.13°C, for animals previously held at 19°C. for 14 hours. The steepness of a temperature gradient was shown to influence the rate of aggregation at a preferendum temperature. At a constant temperature (temperature preferendum) reactions to light were then studied. Light intensity, gradients of light intensity, light quality, and gradients of light quality were considered. Animals were positively phototactic to the range of visible light intensities considered, but became indifferent to light on the addition of chemical substances to the water medium. An absolute optimum light intensity was demonstrated, at which the response to light is greatest in magnitude. The rate of rise of light intensity was shown to be directly related to the magnitude of the response and indirectly related to the time for the response to reach a peak up to the absolute optimum light intensity. The intensity of illumination was inversely related to the time for adaptation to occur. The magnitude of the light response was inversely related to the intensity of a pre-adaptation light stimulus. Wave lengths in the region of 3000 to 3500 Å, with a mean value of approximately 3300 Å, were shown to reverse the primary sign of the phototactic response. The spectral sensitivity curve for the positive phototactic response to visible light extended from 4000 to 6400 Å. Finally, light factors were applied to the animals in a temperature gradient and quantitative data on the response obtained. The interaction of the two factors produced a response which is the resultant of the factors acting in opposition.

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