Iguanas are reptiles and air-breathing vertebrates that must surface to take in oxygen. While they cannot breathe underwater, these lizards have developed remarkable adaptations allowing them to spend significant time submerged. Their ability to hold their breath for extended periods results from specialized physiological mechanisms that manage oxygen use. This strategy varies across species, from terrestrial iguanas using water for evasion to the single species that has fully embraced a marine lifestyle.
Breath-Holding Physiology
When an iguana dives, its body initiates physiological changes designed to conserve its limited oxygen supply. This process, known as the diving reflex, is common among many aquatic and semi-aquatic reptiles.
One important adaptation is bradycardia, a dramatic reduction in heart rate. A diving iguana’s heart rate can drop from around 40 beats per minute to as low as 10 beats per minute, significantly slowing oxygen consumption.
The circulatory system also selectively restricts blood flow to less critical organs, a process called peripheral vasoconstriction. This shunting action ensures that the brain and heart receive the majority of the available oxygenated blood. As the dive continues, muscles rely on anaerobic respiration, a temporary process generating energy without oxygen. This metabolic slowdown allows the iguana to remain underwater.
The Marine Iguana’s Extreme Adaptations
The Galapagos Marine Iguana (Amblyrhynchus cristatus) is the only lizard species globally that forages in the sea. Their dives are for feeding, as they graze exclusively on marine algae attached to submerged rocks. This behavior requires dives up to 30 feet, typically lasting five to ten minutes, though they can remain submerged for 30 minutes or more.
Their bodies exhibit specific physical traits for this marine existence, including a laterally flattened tail that acts as a powerful rudder for swimming. Because they are cold-blooded, iguanas lose body heat rapidly in the cold ocean water, limiting their dive duration.
Upon surfacing, they must immediately bask on black volcanic rocks to restore their body temperature before they can move or digest their meal. A further adaptation involves specialized nasal glands that filter excess salt ingested with the seawater and algae. The iguanas expel this concentrated saline solution through a distinctive “sneezing” action, often leaving a white, salt-encrusted residue on their heads.
Water Habits of Terrestrial Species
In contrast to their marine relative, terrestrial species like the Green Iguana (Iguana iguana) use water primarily as a refuge. These lizards are excellent swimmers, propelling themselves efficiently with powerful, undulating tail movements while keeping their limbs tucked against their sides. They frequently inhabit trees that overhang water, using this position to quickly escape predators.
When threatened, a Green Iguana will drop into the water, relying on its breath-holding capacity for concealment. While they can remain submerged for impressive durations, sometimes up to 30 minutes for survival, these dives are typically short and shallow.
Terrestrial species do not feed underwater; their diet consists of leaves, flowers, and fruit found in the forest canopy. They also use water for regular hydration and soaking, but their primary life activities remain anchored to the land and trees.