Organisms associated with stimulated epipelagic bioluminescence in the Sargasso Sea and the Gulf Stream

On three cruises, vertical profiles of stimulated bioluminescence were measured during the late evening in the upper 200 m of the Sargasso Sea using a submarine photometer. On one cruise, organisms were collected in a 25 μm porosity net after passing through the photometer where the intensity and light content of their bioluminescence were recorded. Correlations of bioluminescence and organisms suggested that the majority of the stimulated bioluminescence produced in the Sargasso Sea was from zooplankton: crustaceans (ostracods, copepods, copepod larvae, euphausid larvae), larvaceans and colonial radiolarians. In addition, the photosynthetic dinoflagellate Pyrocystis noctiluca appeared to produce 5–30% of the measured bioluminescence at some stations. Other dinoflagellates, although numerous, were dim and thus produced less than a few percent of the stimulated bioluminescent light. The subsurface peaks in the Gulf Stream and northern Sargasso Sea were due primarily to ostracods and larvaceans. In the Anegada Passage in October, and in the northern Sargasso Sea and the Gulf Stream in August, there were pronounced subsurface peaks in bioluminescence associated with the thermocline. In Anegada Passage and the Sargasso Sea just north of Puerto Rico in October, and in the Gulf Stream in August, the subsurface bioluminescence peak was in or slightly above the chlorophyll maximum. However, at the Sargasso Sea stations in August, it was 10–40 m above the depth of the chlorophyll maximum.