Bioluminescence in Dinoflagellates

Let’s examine the argument that bioluminescent dinoflagellates are capable of converting kinetic energy into chemical energy—that they are a special type of autotrophic organism that I call kinetitrophic.

There is a special irony here because there are a number of bioluminescent dinoflagellates that have chlorophyll and are capable of photosynthesis, and there are some that do not have chlorophyll.  Those with chlorophyll are already considered autotrophic.  Those without it are considered heterotrophic (that is, in the literature).

Dinoflagellates that are bioluminescent typically live in habitats that have water in motion.  Many live in the open ocean, usually in zones that are affected by waves.  Some live in sheltered bays, but are still exposed to the motion of waves and currents.

These are environments that contain an abundance of kinetic energy that is somewhat random in its actions.

The light from dinoflagellates is a flash of short duration.  It is initiated by a fairly substantial shear force to the cell.  Turbulent flow will initiate it, but laminar flow typically does not.  Note that this is an argument for the kinetitrophic idea—the flash is only initiated when the organism is exposed to substantial (on the cellular scale) kinetic energy.

Some of the dinoflagellate species are relatively large.  When the cells are large or are present in substantial numbers their light can be easily seen by the naked human eye.  However, some species are quite small or can be widely dispersed in the environment.  In those cases the light can only be seen with special instruments that can pick up the low levels of light.  Typically the light emissions are single, bright flashes, although there is a low level continuous emission as well.  The continuous emission is several orders of magnitude lower than the single flashes, and usually only detected by special instruments.

There is no evidence that bioluminescent dinoflagellates can detect their own light or that of other individuals.

There are two leading theories as to why they emit light.  The first is to startle potential predators, and the second is to light the way for potential predators of their predators—the “burglar alarm hypothesis.”  That theory was explored in the National Geographic link of a previous post.

So if the creatures need energy to make light (which is the prevailing view), why do they readily flash in natural phenomena such as waves?  Isn’t that just wasted energy?  And why flash a really dim light?  Is that enough to startle anything or warn anything?

So they live in an environment with plenty of kinetic energy, they flash when exposed to that energy, whether from waves initiated by a potential predator or waves already present in the environment.  They do not seem to be signaling each other.  They can move, but probably not rapidly enough to avoid or cluster around others.  Some of the light that is emitted is so dim that special instruments are needed to detect it. 

But then we hit a speed bump.  Most of what we have discussed so far has favored the kinetitrophic organism model. 

But then there is the issue of circadian rhythms.  Many of these creatures flash only at night, or flash most brightly at night.  How can we explain that?

We will have to discuss that later.


About the roused bear

Nature photographer from central Iowa.
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