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Tammy Frank

Keywords: Neurobiology, vision, vertical migration

The light field in the mesopelagic realm (200-1000 m) consists of primarily blue light from two sources: (1) dim light from the surface, which, due to absorption and scattering, is primarily blue light and (2) bioluminescence, which is also primarily blue light. Therefore, one would expect deep-sea organisms to possess visual pigments that absorb more in than blue compared to shallow water organisms. This has proven to be the case for most deep-sea organisms.

(For a review of visual pigments present in shallow water species, see Goldsmith, 1972; Lythgoe, 1972; Cronin, 1986. For information on the photosensitivities of deep-sea crustaceans, see Frank and Case, 1988a,b; Frank and Widder, 1994a,b; Cronin and Frank, 1996. For information on the visual pigments of deep-sea fish, see Crescitelli, 1991; Partridge et al., 1992; Douglas and Partridge, 1997.)

However, there are some interesting exceptions to this rule. Several species of deep-sea fish possess photophores that emit light primarily in the far red wavelengths (so far red that we can just barely see their light if we're completely dark-adapted), and remarkably, they have several visual pigments, one of which can actually see this far red light (see the bioluminescence section for information on the red bioluminescence, and Partridge and Douglas, 1995 for information on the red-absorbing visual pigments). There are also several species of deep-sea shrimp that possess two visual pigments. One pigment absorbs in the blue (approximately 490-500 nm, as expected), and the second pigment, rather than being a far-red pigment like in the fish, absorbs in the near UV -- about 400 nm (Frank and Case, 1988; Cronin and Frank, 1996). The species that possess this unusual short wavelength pigment have also been shown to be behaviorally very sensitive to UV light (Frank and Widder, 1994 a,b).

What are the possible functions of such a short wavelength pigment? The first thing to realize is that there is enough near-UV light down at 600 m (the daytime depth of these species) for these species to see (see calculation in Frank and Widder, 1994a). One hypothesis is that since the species with two visual pigments (one at 400 nm, and one at 490 nm) are vertical migrators, they might be using the change in the color of light at sunset to cue their migrations.

Vertical migration is the largest animal migration on earth, and occurs in all the world's oceans and lakes. It is the movement of organisms up through the water column at sunset to shallower water, and their movement back down through the water column to deeper water at sunrise. This migration happens every night, and in some areas, the schools of migrating organisms are so massive that the layer can be picked up on shipboard sonars - it looks like the bottom is rising up. The major reason that vertical migrations occur is to avoid predators; these species remain in deeper darker water during the day, and come up at night to feed in the food rich surface water and hide from their own predators under the cover of darkness.

Although this is such a huge and widespread phenomenon, very little is known about the light cues that trigger this massive migration. What is known is that it has to be more than just an intensity change; otherwise, organisms might start migrating during the day on a dark and stormy day, and this doesn't happen. Since the spectral distribution of light changes at sunset, and there's a relative increase of short wavelength light with respect to long wavelength light, we hypothesized that the shrimp that possess both the short and long wavelength visual pigments might be able to sense this spectral cue at sunset (Frank and Case, 1988). However, recent measurements made with an in-situ light meter at 150 m depth from a submersible indicate that the shift in the spectral distribution of light that occurs at the surface at sunset is not seen at this depth (Frank and Widder, 1996).

Since the crustaceans with the near-UV visual pigments start their migrations from 500-600 m depths, they clearly cannot be sensing any changes in the spectral distribution of light at sunset, and must be relying on other cues. This does not answer the question of why these particular species possess this dual visual pigment system, and this does not appear to be a universal phenomenon amoung deep-sea shrimp. We have studied 22 other species of shrimp, including those in the euphausiid, pasiphaeid, penaeid, sergestid, and amphipod families, and it appears that only these genera of caridean shrimp in the family Oplophoridae - Systellaspis, Janicella and Oplophorus - posses this near UV visual pigment in addition to the typical blue absorbing pigment. As there is no funding to study interesting but rare phenomena in the ocean, this question will most likely remain unanswered for a while.

Current research in our laboratory involves determining what light cues are responsible for cuing these massive vertical migrations. Results of recent submersible work in the Gulf of Maine indicate that migration patterns are staggered - i.e. the three species quantified during this study - a euphausiid shrimp Meganyctiphanes norvegica, a cydippid ctenophore Euplokamis sp., and two species of caridean shrimp, Dichelopandalus leptocerus and Pasiphaea multidentata, did not all start their migrations at the same time (Frank and Widder, in press). We are currently conducting further studies to

  1. identify the migration patterns of some of the dominant vertical migrators in the Gulf of Maine;
  2. determine whether the initiation of the migration can be cued to some changing characteristic in the downwelling light field at sunset (see our web page for description of light meters being used);
  3. determine whether the differences in migration patterns are related to differences in photosensitivity (via electrophysiological and behavioral studies), and/or differences in their swimming speeds. In addition to electrophysiological measurements of photosensitivity, flicker fusion frequencies (as an indication of temporal resolution) will also be studied and correlated with habitat depth of the various organisms under examination.


  • Crescitelli, F. 1991. Adaptations of visual pigments to the photic environment of the deep sea. J. Expt. Zool Supp. 5: 66-75.
  • Cronin, T.W. 1986. Photoreception in marine invertebrates. Amer. Zool 26: 403-415.
  • Cronin,T.W. and Frank, T.M. 1996. A short-wavelength photoreceptor class in a deep-sea shrimp. Proc. R. Soc. Lond. B 263: 861-865
  • Douglas, R.H. and Partridge, J.C. 1997. On the visual pigments of deep-sea fish. J. Fish Biol. 49
  • Frank, T.M. and Case, J.F. 1988a. Visual spectral sensitivities of bioluminescent deep-sea crustaceans. Biol. Bull. 175: 261-273.
  • Frank, T.M. and Case, J.F. 1988b. Visual spectral sensitivity of the bioluminescent deep-sea mysid, Gnathophausia ingens. Biol. Bull. 175: 274-283.
  • Frank, T.M. and Widder, E.A. 1994a. Comparative study of behavioral-sensitivity thresholds to near-UV and blue-green light in deep-sea crustaceans. Mar. Biol. 121: 229-235.
  • Frank, T.M. and Widder, E.A. 1994b. Evidence for behavioral sensitivity to near-UV light in the deep-sea crustacean Systellaspis debilis. Mar. Biol. 118: 279-284.
  • Frank,T.M. and Widder,E.A. 1996. UL light in the deep-sea: In situ measurements of downwelling irradiance in relation to the visual threshold sensitivity of UV-sensitive crustaceans. Mar. Fresh. Behav. Physiol. 27(2-3): 189-197.
  • Goldsmith, T.H. 1972. The natural history of invertebrate visual pigments. In: Handbook of Sensory Physiology, Vol. VII/l : 727-742.
  • Lythgoe, J.N. 1972. The adaptation of visual pigments to the photic environment. Handbook of Sensory Physiology Vol. VII/I : 566-603.
  • Partridge, J.C., Archer, S.N., and Van Oostrum, J. 1992. Single and multiple visual pigments in deep-sea fishes. J. mar. biol. Ass. U. K. 72 : 113-130.
  • Partridge, J.C. and Douglas, R.H. 1995. Far-red sensitivity of dragon fish. Nature 375: 21-22.

Submitted: 24 Oct 97

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Tammy Frank |
Harbor Branch Oceanogr. Inst. |
5600 U.S. Hwy 1 North | HBOI Bioluminescence Web Page
Ft. Pierce, FL 34946 |
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