The Glaucus atlanticus, commonly known as the blue dragon sea slug, is a small, striking marine gastropod. Typically around 3 centimeters (1.2 inches) long, it exhibits a blue and silver coloration, with its blue side facing upwards to blend with the ocean’s surface and its silvery-grey underside facing downwards to camouflage against the bright water below. Blue dragons spend their lives floating upside-down in the open ocean, carried by winds and currents, utilizing an air bubble in their stomach for buoyancy. This unique pelagic lifestyle is complemented by a diet central to its survival and defense in the marine environment.
The Blue Dragon’s Main Meal
The blue dragon sea slug is a carnivore that primarily preys on other venomous pelagic organisms. Its primary food source is the Portuguese Man O’ War (Physalia physalis), a siphonophore known for its powerful stinging tentacles. Blue dragons can consume prey much larger than themselves, including substantial portions of the Man O’ War. Beyond the Portuguese Man O’ War, the blue dragon also feeds on other stinging creatures that float on the ocean’s surface, such as the by-the-wind sailor (Velella velella) and the blue button (Porpita porpita). The blue dragon’s ability to consume these venomous organisms is attributed to its immunity to their stinging cells.
Ingesting Dangerous Prey
The Glaucus atlanticus possesses specialized adaptations to consume venomous prey without sustaining harm. Its mouth is equipped with a strong jaw and a radula, a ribbon-like structure covered in serrated teeth. This unique dental structure allows the sea slug to grasp and tear apart the tissues and tentacles of its prey. It consumes chunks of the venomous organism. The sea slug has physiological mechanisms that render it immune to the toxins produced by the stinging cells of its prey. This immunity allows the blue dragon to ingest these dangerous components without triggering a harmful reaction within its body, contributing to its unique defensive strategy.
Turning Venom Into Defense
After ingesting its venomous prey, the blue dragon sea slug employs a process known as kleptocnidae, isolating undischarged stinging cells (nematocysts) instead of digesting them. These potent nematocysts are then transported through the slug’s digestive system to specialized sacs, known as cnidosacs, located at the tips of its appendages called cerata. The blue dragon concentrates the most powerful nematocysts it acquires, turning the venom into its own defense mechanism. When threatened by a predator, the blue dragon can release these stored stinging cells, delivering a sting that can be even more potent than that of its original prey. This adaptation provides a formidable deterrent to potential attackers, and human contact can result in a painful and potentially dangerous sting.