Deep sea benthic bioluminescence at artificial food falls, 1,000-4,800m depth, in the Porcupine Seabight and Abyssal Plain, North East Atlantic Ocean

Natural bioluminescence (that not mechanically stimulated by human intervention) produced by organisms on the seafloor of the northeast Atlantic ocean between 970 and 4,800 m depth was examined using an image intensifying (ISIT) camera mounted on an autonomous lander system. In the absence of bait little or no luminescence was observed but with bait present there was a significant inverse relationship with depth, Log(10) (1 + number of events h(-1)) = 1.7627-0.3235 depth (km) (r(2) = 0.8158, P < 0.001) indicating an average of 2.6 events h(-1) at 4 km and 28 h(-1) at 1 km. But in an area at ca. 1 km depth near carbonate and coral mounds the mean was 133 events h(-1), much higher than predicted. In this bioluminescent hot spot 52-483 events h(-1) were observed including moving luminescent targets and release of patches of luminescent material into the water around the bait so that on occasions the whole area around the bait was illuminated persisting on a time scale of minutes. At abyssal depths, luminescence was much less than reported at similar depths in the tropical NE Atlantic off Cape Verde. The sources of luminescence could not be determined but in the most active areas were associated with presence of eels Synaphobranchus kaupii which although themselves not luminescent may have stimulated luminescence from prey organisms such as ostracods (Vargula norvegica).