Deep-sea bioluminescence of the porcupine seabight and porcupine abyssal plain, NE Atlantic Ocean
To examine deep-sea bioluminescence in situ, observations were made using an intensified (ISIT) camera mounted on an autonomous lander, at the Porcupine Seabight and Abyssal Plain regions of the north-east Atlantic ocean. The vertical distribution of bioluminescence (down to 4800m depth) showed an exponential disease in the number of organisms that could be mechanically simulated to emit light. Autumn profiles showed a deep luminescent layer (40 events/m -3) between 1200 and 1600m, which was not present in spring deployments (10 events/m-3). Above this a layer of warm, high salinity Mediterranean-derived water was identified and it is suggested that bioluminescent organisms were trapped below this layer due to its physical properties. Static benthic studies examined the distribution of organisms that emitted bioluminescence, without extrinsic stimulation, in the presence of bait. Of the eleven deployment locations, one site (ca. 51°10'N, 11°40'W) recorded an average of 3.52 bioluminescent events per minute, compared to 0.37 events at other locations (at depths from 970m-4000m). At this bioluminescent hotspot, organisms attracted into the field of view did not include known luminous species. This suggested the involvement of small epibenthic or infaunal organisms that produced light as a defensive reaction to the activity of organisms at bait. The difficulty in maintaining deep-sea organisms in a laboratory has limited the study of the ecological function of bioluminescent emissions. To investigate the use of bioluminescent emissions as intraspecific signals, studies were performed in the laboratory with shallow water bioluminescent ophiuroids (Amphiura filiformis ). The emissions were initiated by chemical stimulation and were associated with limb autonomy, typical of a defensive response. No evidence was found for the use of bioluminescence as an intraspecific signal.