Underwater Light Regime Research Articles

Bioluminescence and luminescent fish in the Strait of Messina from the mesoscaph ?Forel?

Light irradiance was measured at 430, 470 and 500 nm aboard the mesoscaph “Forel” in the Strait of Messina from the surface to 550 m depth in May 1979. The underwater light regime is partly due to the downwelling residual sunlight and partly to bioluminescence. An intense bioluminescence is localized at about 450 m at midday and moves upwards in the evening to reach an area extending from 100 m depth to the surface late in the evening. Two types of luminescence were observed: one associated with luminescent organisms and another diffuse, probably due to bacteria. Three types of luminescent fish were recognized, namely Argyropelecus hemigymnus, myctophids and Cyclothone braueri, and their time and space distribution were studied. While myctophids were encountered from the surface (21:00 hrs) to 550 m depth (16:00 hrs), A. hemigymnus were only observed between 180 m (19:45 hrs) and 500 m (12:15 hrs), and C. braueri between 330 m (16:00 hrs) and 500 m (19:00 hrs). The results do not show a significant relation between the absolute ambient light intensity and the time or the depth where the fish were observed.