JOHNSEN, S.; Duke University: The red and the black: Bioluminescence and the color of animals in the deep sea

Unlike terrestrial and near-shore species, the coloration of deep-sea animals is quite uniform among species, families, and even phyla. The colors of these species are generally assumed to be cryptic, but it is not known how cryptic they are and under what conditions. This study measured the color of approximately 75 deep-sea species, both pelagic and benthic, and compared the results to two sets of predictions: 1) optimal crypsis under environmental light, 2) optimal crypsis when viewed by bioluminescent “searchlights”. The reflectances of the pelagic species at the blue-green wavelengths important for deep-sea vision were far lower than the predicted reflectances for crypsis under environmental light and closer to the predictions for crypsis under searchlights. This suggests that bioluminescence is more important than environmental light for detecting animals at mesopelagic depths. The reflectances of the benthic species were highly variable and a relatively poor match to the substrates on which they were found. However, estimates of the contrast sensitivity of deep-sea visual systems suggest that even a poor match may be sufficient for crypsis. With a few interesting exceptions, body coloration was uniform.