Studies on the occurrence, physiology, and ecology of bioluminescence in dinoflagellates

Graduation date: 1973To provide further information on the occurrence and geographical\ud variations of bioluminescent capabilities of marine dinoflagellates,\ud forty species, representing twelve genera, of dinoflagellates\ud from Yaquina Bay, Oregon, were examined for bioluminescence as\ud single cell isolates. Seventeen species from the genera Ceratium\ud (1 sp.), Gonyaulax (3 sp.), and Peridinium (13 sp.) were found to be\ud bioluminescent. Ceratium fusus was the only member of the genus\ud found to emit light; G. triacantha was found to be non-bioluminescent.\ud The total photon emission of each luminescent species is reported.\ud Values ranged from 1.05 x 10¹⁰ photons per P. depressum\ud to 2.1 x 1O⁷ photons per G. digitale. As a taxon, the genus\ud Peridinium emitted more light by an order of magnitude than did\ud Ceratium or Gonyaulax. Comparisons with previous reports are\ud made.\ud Photoinhibition of the mechanical receptor mechanism is\ud largely responsible for orders of magnitude diel variations of stimulable\ud bioluminescence in the auxotrophic dinoflagellates. The\ud mechanically stimulable bioluminescence of members of the\ud Gonyaulax catenella group can be photoinhibited completely by exposure\ud to as little as 10¹³ quanta/cm² delivered as a pulse of width\ud between 0.1 and 10 seconds. There is an initial time lag of one\ud minute, followed by a first order decay to approximately one percent\ud of the bioluminescence of unexposed controls. The half time of this\ud decay is only 50 seconds.\ud Action spectra for photoinhibition in Gonyaulax catenella, G.\ud acatenlla, and G. tamarensis revealed a single absorption band with\ud a maximum at 562 nm. Photoinhibition appears to raise the threshold\ud of sensitivity of the shear receptor mechanism. Chemically stimulable\ud bioluminescence is unaffected by these brief exposures to light.\ud Grazing experiments were conducted with three calanoid copepods\ud and three species of bioluminescent dinoflagellates, using\ud procedures which yielded samples of cultures with high and low\ud capacities for mechanically stimulable bioluminescence. In all cases\ud the ingestion rates were lower for the high bioluminescent capacity\ud samples than for the samples having a reduced bioluminescent\ud capacity. These results indicate that dinoflagellate bioluminescence\ud has survival value as a defense against copepod grazing. Of several possible mechanisms, we propose that the flash is a visual, protean\ud display which startles or confuses the copepod sufficiently to allow\ud the dinoflagellate to escape. The net evolutionary value is that predation\ud would be reduced on a dinoflagellate population as a whole