SPONTANEOUS AND STIMULATED BIOLUMINESCENCE OF THE DINOFLAGELLATE CERATOCORYS HORRIDA (PERIDINIALES)

This is the first report of spontaneous bioluminescence in the autotro phic dinoflagellate Ceratocorys horrida von Stein. Bioluminescence was measured, using an automated data acquisition system, in a strain of cultured cells isolated from the Sargasso Sea. Ceratocorys horrida is only the second dinoflagellate species to exhibit rhythmicity in the r ate of spontaneously flashing, flash quantum flux (intensity), and lev el of spontaneous glowing. The rate of spontaneous flashing was maxima l during hours 2-4 of the dark phase [i.e, circadian time (CT) 16-18 f or a 14:10 h LD cycle (LD14:10)] with approximately 2% of the populati on flashing(.)min(-1), a rate approximately one order of magnitude gre ater than that of the dinoflagellate Gonyaulax polyedra. Flash quantum flux was also maximal during this period. Spontaneous flashes were 13 4 ms in duration with a maximum flux (intensity) of 3.1 x 10(9) quanta (.)s(-1). Light emission presumably originated from blue fluorescent m icrosources distributed in the cell periphery and not from the spines. Values of both spontaneous flash rate and maximum flux were independe nt of cell concentration. Isolated cells also produced spontaneous fla shes. Spontaneous glowing was dim except for a peak of 6.4 x 10(4) qua nta(.)s(-1.)cell(-1), which occurred at CT22.9 for LD14:10 and at CT22 .8 for LD12:12. The total integrated emission of spontaneous flashing and glowing during the dark phase was 4 x 10(9) quanta cell(-1), equiv alent to the total stimulable luminescence, The rhythms for C. horrida flash and glow behavior were similar to those of Gonyaulax polyedra, although flash rate and quantum flux were greater. Spontaneous biolumi nescence in C. horrida may be a circadian rhythm because if persisted for at least three cycles in constant dark conditions. This is also th e first detailed study of the stimulated bioluminescence of C. horrida , which also displayed a diurnal rhythm. Cultures exhibited > 200 time s more mechanically stimulated bioluminescence during the dark phase t han during the light phase. Mechanical stimulation during the dark pha se resulted in 6.7 flashes(.)cell(-1); flashes were brighter and longe r in duration than spontaneous flashes. Cruise-collected cells exhibit ed variability in quantum flux with few differences in flash kinetics. The role of dinoflagellate spontaneous bioluminescence in the dynamic s of near-surface oceanic communities is unknown, but it may be an imp ortant source of natural in situ bioluminescence.