Iguanas are large, sun-loving lizards inhabiting tropical and subtropical regions, often seen basking on rocks or climbing trees. While most species, such as the Green Iguana, are primarily terrestrial, they possess a remarkable ability to navigate and survive in aquatic environments. This capability involves a physiological transformation that allows them to become temporary masters of the underwater world. The length of time an iguana can remain submerged showcases a complex survival mechanism that maximizes oxygen conservation.
Maximum Dive Duration and Species Variation
The maximum time an iguana can stay submerged varies significantly between species, correlating with their reliance on aquatic habits. The Galapagos Marine Iguana, the world’s only sea-going lizard, holds the record for the longest duration, capable of remaining underwater for up to 30 to 45 minutes. Typical foraging dives for this species, however, usually last between 5 and 10 minutes.
This endurance is necessary for the Marine Iguana, which must dive into cold Pacific waters to graze on marine algae. Terrestrial species, such as the Green Iguana, also exhibit substantial aquatic ability, though their dives are shorter and primarily defensive. A Green Iguana can hold its breath for up to 30 minutes when escaping a predator.
Physiological Mechanisms for Extended Dives
The ability of iguanas to sustain life without breathing for lengthy periods is rooted in physiological adjustments known as the dive reflex. This process begins with a dramatic reduction in heart rate, called bradycardia. For example, a Marine Iguana’s heart rate can slow from a resting rate of around 40 beats per minute (bpm) down to as low as 10 bpm during a deep dive.
This slowing of the heart suppresses the overall metabolic rate, significantly decreasing the body’s demand for oxygen. The lizard also employs peripheral vasoconstriction, or blood shunting, restricting blood flow to the limbs and non-vital organs. This ensures the limited oxygen supply is prioritized for sensitive organs, specifically the brain and the heart.
As an ectotherm, the iguana’s body temperature is regulated by its external environment, and cold water aids its dive capacity. The cooler temperature naturally slows metabolic processes, reducing the rate at which oxygen is consumed. Once the dive exceeds oxygen reserves, the muscles switch to anaerobic respiration, allowing for a final push of activity before the iguana must surface.
Why Iguanas Dive: Behavior and Ecology
Iguanas primarily enter the water for two ecological reasons: to forage and to evade threats. For the Marine Iguana, diving is a necessary behavior for survival, as it is the only lizard that feeds exclusively on marine algae found in the intertidal and subtidal zones. Large males often dive deeper and longer to access abundant algal beds not exposed during low tide.
For both marine and terrestrial iguanas, water serves as an immediate escape route from predators. When faced with a threat, a terrestrial iguana will launch itself into a nearby river or pond. This allows the reptile to quickly disappear and remain motionless underwater until the danger has passed. These defensive dives are typically shorter than foraging dives, focusing on rapid concealment and stillness.