HCNSO Student Theses and Dissertations

Defense Date


Document Type


Degree Name

M.S. Marine Biology

First Advisor

Tamara Frank, Ph.D.

Second Advisor

Patricia Blackwelder, Ph.D.

Third Advisor

Heather Bracken-Grissom, Ph.D.


Counterillumination, the mechanism by which pelagic species produce bioluminescence to replace the light blocked by their bodies to hide their silhouettes, has been known for over 100 years. However, little is known about how these animals are able to so precisely replicate the intensity of downwelling light. The recent discovery of opsins in photophores (Bracken-Grissom et al. 2020) suggests that these autogenic organs (i.e. non-bacterial) may be sensitive to light, in addition to their function of emitting visible light. The study presented here is 1) the first ultrastructural assessment of photophores in species Systellaspis debilis, Janicella spinicauda, Parasergestes armatus, and Allosergestes sargassi and 2) the first study to examine ultrastructural changes in photophore organelles in response to light. The results of this study, demonstrate that photophore organelles exhibit changes in response to light similar to that seen in crustacean photoreceptors, and provides strong support for the hypothesis that the photophores themselves are sensitive to light.


NSF Grant DEB-1556059