UV light in the deep-sea: In situ measurements of downwelling irradiance in relation to the visual threshold sensitivity of UV-sensitive crustaceans

Several species of deep-sea crustaceans possess unusually high spectral sensitivity to UV light, measured elec-trophysiologically. In addition, behavioral experiments indicate that these species are equally sensitive to near-UV and blue-green light. These results raised questions about the functional significance of this short wavelength sensitivity, since it is commonly believed that UV light is virtually absent in the deep-sea. Using submersible based technology, we conducted measurements of downwelling irradiance at two wavelengths - 380 and 480 nm. These measurements indicate that the irradiance of 380 nm light at 500–600 m, the daytime depth range of the crustaceans with a U V sensitivity peak, is high enough to be detected by these species.