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