Bioluminescence in the ocean: origins of biological, chemical, and ecological diversity.

From bacteria to fish, a remarkable variety of marine life depends on bioluminescence (the chemical generation of light) for finding food, attracting mates, and evading predators. Disparate biochemical systems and diverse phylogenetic distribution patterns of light-emitting organisms highlight the ecological benefits of bioluminescence, with biochemical and genetic analyses providing new insights into the mechanisms of its evolution. The origins and functions of some bioluminescent systems, however, remain obscure. Here, I review recent advances in understanding bioluminescence in the ocean and highlight future research efforts that will unite molecular details with ecological and evolutionary relationships.

Bioluminescence in the Deep-Sea Cirrate Octopod Stauroteuthis syrtensis Verrill (Mollusca: Cephalopoda).

The emission of blue-green bioluminescence ({lambda}max = 470 nm) was observed from sucker-like structures arranged along the length of the arms of the cirrate octopod Stauroteuthis syrtensis. Individual photophores either glowed dimly and continuously or flashed on and off more brightly with a period of 1-2 seconds. Examination of the anatomy and ultrastructure of the photophores confirmed that they are modified suckers. During handling, the photophores were unable to attach to surfaces, suggesting that, unlike typical octopod suckers, they have no adhesive function. The oral position of the photophores and the wavelength of peak emission, coupled with the animals' primary postures, suggests that bioluminescence in S. syrtensis may function as a light lure to attract prey.

Transparency and Visibility of Gelatinous Zooplankton from the Northwestern Atlantic and Gulf of Mexico.

Transparency measurements (at 400 to 700 nm) were made on living specimens of 29 common species of gelatinous zooplankton from the Northwestern Atlantic Ocean and Gulf of Mexico. Percent transparency ranged from 91% for the hydromedusa Sibogota typa to 0.51% for the pteropod Clione limacina. Percent transparency was linearly and positively correlated with wavelength, with slopes of the regression lines (normalized to the percent transparency at 480 nm) ranging from 0.027%/nm for Sibogota typa to 0.51%/nm for the ctenophore Mnemiopsis macrydi (average 0.17 +/- 0.019%/nm). There was no significant correlation between the percent transparency of an animal and its daytime depth distribution. The relationship between percent transparency and sighting distance when viewed from below was modeled and showed that, due to the increase of the minimum contrast threshold for object detection at lower light levels, the usefulness of transparency as camouflage increases dramatically with depth. A preliminary account of these results was presented by the authors at the fourteenth meeting of the Ocean Optics Society in November 1998.

Shewanella woodyi sp. nov., an exclusively respiratory luminous bacterium isolated from the Alboran Sea.

Thirty-four strains of nonfermentative, respiratory, luminous bacteria were isolated from samples of squid ink and seawater from depths of 200 to 300 m in the Alboran Sea. Although these strains had a few properties similar to properties of Shewanella (Alteromonas) hanedai, they did not cluster phenotypically with any previously described bacterium. The nucleotide sequence of a 740-bp segment of luxA was not homologous with other known luxA sequences but clustered with the luxA sequences of Shewanella hanedai, Vibrio logei, Vibrio fischeri, and Photobacterium species. The 16S RNA gene from two strains was sequenced and was found to be most closely related to the S. hanedai 16S RNA gene. Based on the differences observed, we describe the new isolates as members of new species, Shewanella woodyi sp. nov. Strain ATCC 51908 (= MS32) is the type strain of this new species.

Patterns of Stimulated Bioluminescence in Two Pyrosomes (Tunicata: Pyrosomatidae).

Pyrosomes are colonial tunicates that, in contrast with typical luminescent plankton, generate brilliant, sustained bioluminescence. They are unusual in numbering among the few marine organisms reported to luminesce in response to light. Each zooid within a colony detects light and emits bioluminescence in response. To investigate the luminescence responsivity of Pyrosoma atlanticum and Pyrosomella verticillata, photic, electrical, and mechanical stimuli were used. Photic stimulation of 1.5 x 109 photons{middot}s-1{middot}cm-2, at wavelengths between 350 and 600 nm, induced bioluminescence, with the maximum response induced at 475 nm. The photic-excitation half-response constant was 1.1 x 107 photons{middot}s-1{middot}cm-2 at 475 nm for P. atlanticum; P. verticillata had a significantly higher half-response constant of 9.3 x 107 photons{middot}s-1{middot}cm-2. Individual zooids within a colony, however, appeared to have different half-response constants. Stimulus strength influenced recruitment of zooids and, in turn, luminescent duration and quantum emission. Image intensification revealed saltatory propagation of luminescence across the colony, owing to photic triggering among zooids. Repetitive, regular mechanical or electrical stimulation elicited rhythmic flashing characterized by alternating periods of high and low light intensities.

The visual pigments of four deep-sea crustacean species.

The visual pigments of four mesopelagic crustacean species were studied at sea by means of microspectrophotometry. The absorbance maxima obtained for the visual pigments and their metarhodopsins, respectively, were: 493 nm and 481 nm (Systellaspis debilis), 485 nm and 480 nm (Acanthephyra curtirostris), 491 nm and 482 nm (A. smithi), and 495 nm and 487 nm (Sergestes tenuiremis). The spectral characteristics of the rhodopsins and metarhodopsins permit high photosensitivity and facilitate photoregeneration in a nearly monochromatic environment. Photic regeneration of rhodopsins from the deep-sea environment was demonstrated, and data were obtained which are consistent with the occurrence of dark regeneration. Specific optical density of the observed visual pigments was calculated for two species.

A multichannel microspectrophotometer for visual pigment investigations.

The microspectrophotometer described replaces the photomultiplier of conventional scanning systems with a multichannel detector. By eliminating scanning-related artifacts, particularly those associated with mechanical vibrations, this system makes possible ship-based microspectrophotometric studies of visual pigments of marine organisms too fragile for live transport to shore-based laboratories. The performance of the multichannel microspectrophotometer is compared with that of conventional scanning systems and absorbance spectra taken at sea on isolated rhabdoms from Euphausia pacifica are presented. Difference spectra gave a lambda max for rhodopsin of 483 nm and a lambda max for metarhodopsin of 489 nm.

Far red bioluminescence from two deep-sea fishes.

Spectral measurements of red bioluminescence were obtained from the deep-sea stomiatoid fishes Aristostomias scintillans (Gilbert) and Malacosteus niger (Ayres). Red luminescence from suborbital light organs extends to the near infrared, with peak emission at approximately 705 nanometers in the far red. These fishes also have postorbital light organs that emit blue luminescence with maxima between 470 and 480 nanometers. The red bioluminescence may be due to an energy transfer system and wavelength-selective filtering.