THE OCCURRENCE OF DINOFLAGELLATE LUMINESCENCE AT WOODS HOLE

1. Bioluminescence in the water in Woods Hole was measured once a week from November, 1965, to November, 1966, and was related to the occurrence of armored luminescent dinoflagellates. 2. Thirty-two species of dinoflagellates were identified, 23 of these were tested for luminescence as isolated cells. Sixteen species were found to be luminescent. 3. Population densities of dinoflagellate species were measured by counting individuals screened from water samples. The concentrations of luminescent species varied from nearly 1000 cells per liter in February, 1966, to less than 5 cells per liter during June and July, while total dinoflagellates ranged from more than 4000 cells per liter to 5 cells per liter. 4. Amounts of luminescence radiometrically recorded in air-bubble-stimulated water samples correlated with the numbers of luminescent armored dinoflagellates present. Exceptions to this correlation were found when population densities were too high for the radiometric recording techniques to be accurate and during May and August, 1966, when the luminescent organisms were too small to be collected and counted. 5. Endogenous diurnal rhythms of flashing were found only during August, 1965 (Kelly and Katona, 1966). 6. Light inhibition of flashing was found whenever it was tested (at least once each month), although sensitivity to light inhibition varied greatly-as little as 1 second of exposure to 350 lux illumination reduced flashing by ⅔. 7. The ecology and evolution of luminescent dinoflagellates are discussed. It is suggested that dinoflagellates are responsible for most near-surface luminescence, that luminescent forms are derived from a single common ancestor, that the ability serves an adaptive function, as yet undetermined, and that much more work on a number of areas will be required before a detailed ecological understanding of dinoflagellate luminescence is obtained.