AN ENDOGENOUS DIURNAL RHYTHM OF BIOLUMINESCENCE IN A NATURAL POPULATION OF DINOFLAGELLATES

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Abstract
Most dinoflagellate species and individuals taken from Eel Pond during this study were luminescent and these were sufficient in abundance to explain all the luminescence recorded. This is probably the case in many marine environments. Macroscopic organisms capable of luminescence were removed by filtration, and the only microplankton constituents capable of luminescence and present in sufficient numbers were dinoflagellates. Dinoflagellate luminescence is commonly a cause of light production in surface regions of the ocean (Harvey, 1952 ; Hastings, 1963) and more knowledge is needed of the luminescent behavior of individuals and cultures of the various species. The effects of temperature, depth and other environmental conditions are unknown. Spontaneous luminescence without stimulation was observed in the laboratory, but is very variable and its extent in the natural environment is not known. Much work is needed on the ecology of dinoflagellate luminescence. The rate of luminescent flashing of natural populations following stimulation is greatest at night, is controlled by an endogenous diurnal rhythm, and is inhibited by light. The sensitivity to light-inhibition is also controlled by an endogenous rhythm, and is greatest during midday when flashing is least. Thus in the natural environment, light-inhibition and an endogenous rhythm act together in decreasing stimulated daytime luminescence.

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