Cephalopod Predation Facilitated by Dinoflagellate Luminescence

Predation by nocturnal cephalopods on nonluminous prey was examined in the presence of dinoflagellate bioluminescence. Sepia officinalis Linnaeus and Euprymna scolopes Berry were tested for predation efficiency in darkness illuminated by the luminescent dinoflagellate Pyrocystis fusiformis Murry. Prey were mysids, Holmesimysis sculpta (Tattersall); grass shrimp, Palaemonetes pugio Holthuis; and mosquito fish, Gambusia affinis Baird and Girard. Tests were conducted in aquaria containing 0-20 cells ml-1 of P. fusiformis. Predation increased as numbers of luminescent dinoflagellates increased. Controls were predation tests in the presence of P. fusiformis during nonluminescent photophase or in the absence of dinoflagellates. Movements of squid and prey readily stimulated luminescence. Behavior and correlated luminescence in infrared-illuminated aquaria were recorded by image-intensified and infrared video cameras. Sepia strikes on prey were common under luminescent conditions--85% occurred in less than 10 min; but strikes in darkness were rare. E. scolopes attacked more frequently than Sepia, and almost 90% obtained prey under luminescent conditions. This study demonstrates the ability of squid to use dinoflagellate bioluminescence to locate and capture nonluminous prey. The burglar alarm theory of the adaptive significance of dinoflagellate bioluminescence is supported.