Bioluminescence in the deep sea: Free-fall lander observations in the Atlantic Ocean off Cape Verde

摘要

A novel autonomous free-fall lander vehicle, with a capability down to 6000 m, was deployed off Cape Verde for studies on bioluminescence in the deep sea. The system was equipped with a high-sensitivity Intensified Silicon Intensified Target (ISIT) video camera, a programmable control-recording unit and an acoustic current meter with depth and temperature sensors. The ISIT lander was used in three modes: (1) free falling at 34 m min~(-1), with the camera looking downwards at a mesh screen, recording impacts of luminescent organisms to obtain a vertical profile down to the abyssal sea floor, sampling at > 100 1 s~(-1); (2) rotating, with the lander on the sea floor and the camera orienting to the bottom current using a servo-controlled turntable, impacts of luminescent organisms carried by the bottom current onto a mesh screen mounted 0.5 m in front of the camera were recorded to estimate abundance in the benthic boundary layer; (3) baited, with the camera focused on a bait placed on the sea floor. Profiles recorded abundance of luminescent organisms as 26.7 m~(-3) at 500-999 m depth, decreasing to 1.6 m~(-3) at 2000-2499 m and 0.5 m~(-3) between 2500 m and the sea floor at 4046 m, with no further detectable significant change with depth. Rotator measurements at a 0.5 m height above the sea floor gave a mean abundance of 0.47 m~(-3) in the benthic boundary layer at 4046 m and of 2.04 m~(-3) at 3200 m. Thirty five minutes after the bait was placed on the sea floor at 3200 m, bioluminescent fauna apparently arrived at the bait and produced luminescent displays at a rate of 2 min~(-3). Moving, flashing light sources were observed and luminescent material was released into the bottom current.