Bioluminescence of the poecilostomatoid copepod Oncaea conifera

Abstract

The small poecilostomatoid copepod Oncaea conifera Giesbrecht bears a large number of epidermal luminous glands, distributed primarily over the dorsal cephalosome and urosome. Bioluminescence is produced in the form of short (80 to 200 ms duration) flashes from withrn each gland and there IS no visible secretory component. Nevertheless each gland opens to the exterior by a simple valved pore. Intact copepods can produce several hundred flashes before the luminescent system is exhausted. Individual flashes had a maximum measured flux of 7.5 X 10" quanta s ', and the flash rate follows the stimulus frequency up to 30 S" Video observations show that ind~vidual glands flash repeatedly and the flash propagates along their length. The gland gross morphology is highly variable although each gland appears to be unicellular. The cytoplasm contains a n extensive endoplasmic reticulum. 0. conifera swims a t Reynolds numbers of 10 to 50, and is normally associated with surfaces (e.g. marine snow). We suggest that the unique anatomical and physiological characteristics of the luminescent system arc related to the specialised ecological niche occupied by this species. Flashing is interpreted as a defensive response to potential predators.