Variation in bioluminescence with ambient illumination and diel cycle in acosmopolitan ophiuroid (Echinodermata)

Luminescence intensity and kinetics of the small cosmopolitan ophiuroid Amp hipholis squamata were measured in the laboratory from individuals collecte d in a bright intertidal environment and a dark subtidal environment (15 m depth). Luminescence was also measured during day and night for intertidal individuals only. Luminescence intensity was about 100 times higher for int ertidal individuals than for subtidal individuals, and about 2 times higher during day time than at night for intertidal individuals. It is the first time that luminescence intensity has been shown to vary with depth and betw een day and night in a benthic invertebrate species. Conversely luminescenc e kinetics, were always similar whatever the origin of the sample and time of measurement. Our results support the common belief that differences in l uminescence intensity reflect differences in ambient illumination [obtainin g enough contrast with the least signal] more than being related to any oth er environmental parameter.