AN ENCOUNTER MODEL TO PREDICT NATURAL PLANKTONIC BIOLUMINESCENCE

Natural bioluminescence results from the emissions of bioluminescent organisms in the absence of man-made disturbance. Most epipelagic and mesopelagic bioluminescence is caused by plank-tonic organisms. Limited attempts to measure natural bioluminescence in situ with surface deployed and moored instruments have recorded much higher levels of natural bioluminescence than have been observed from submersibles. We present a model predicting the frequency of interactions among planktonic organisms leading to natural bioluminescent emissions. The results suggest that natural bioluminescent flashes caused by interactions between zooplankters may be rare events in the Sargasso Sea, with our model predicting a maximum of nearly 600 flashes h-1 m-3 at night in surface waters of the northern Sargasso Sea where there was an unusually high concentration of euphausiids and small bioluminescent dinoflagellates, but < 1 flash h-1 m-3 in the southern Sargasso Sea. In both locations most of the natural bioluminescence was predicted to be caused by euphausiids and copepods of the genus Pleuromamma and natural bioluminescence generally decreased with depth. The more intense displays of natural bioluminescence are probably the result of the bioluminescence of numerous smaller dinoflagellates common in coastal waters and may also be the result of disturbances caused by interactions of larger organisms with bioluminescent plankters.