Marine iguanas, found exclusively in the Galápagos Islands, are the world’s only seagoing lizards, thriving where land meets ocean. Their lifestyle involves diving into cold Pacific waters for food, raising questions about their survival without gills.
Respiratory System of Marine Iguanas
Marine iguanas do not possess gills; they breathe air using lungs. Their ability to spend significant time underwater comes from a capacity to hold their breath for 30 to 40 minutes, sometimes up to an hour. This breath-holding is crucial for their marine existence, allowing them to forage for algae on the seabed.
Several physiological adjustments enable these extended dives. When submerged, a marine iguana’s heart rate can slow, a phenomenon known as bradycardia, decreasing from 40 to as low as 10 beats per minute underwater. This reduction in heart rate helps to conserve oxygen by lowering their metabolic rate. Blood flow is also strategically redistributed, or shunted, to ensure that oxygen-sensitive organs like the brain and heart receive adequate supply, while less essential tissues receive reduced circulation. Marine iguanas also possess a higher concentration of red blood cells, enhancing their blood’s capacity to store oxygen for longer underwater excursions; however, most foraging dives are much shallower and last between 5 to 10 minutes, despite their ability to dive to 98 feet (30 meters).
Specialized Marine Adaptations
Beyond their respiratory adaptations, marine iguanas exhibit other specialized traits for survival in the challenging Galápagos marine environment. One such adaptation involves their salt glands, located near their nostrils. These glands filter excess salt ingested from seawater and algae, which is then expelled through a “sneeze-like” action. The expelled salt often leaves a noticeable white crust on their heads.
As cold-blooded reptiles, marine iguanas rely on external heat sources to regulate their body temperature. Their dark skin pigmentation is effective at absorbing solar radiation, allowing them to rapidly warm up after a cold dive. They engage in basking behavior on the dark volcanic rocks, aiming to raise their body temperature to an optimal 35 to 39 degrees Celsius. During cooler periods, they may huddle together in groups, demonstrating communal thermoregulation to minimize heat loss.
Marine iguanas are herbivores, feeding primarily on marine algae, primarily red and green varieties. Their blunt snouts and sharp, tricuspid teeth are adapted for scraping algae off submerged rocks. Larger males undertake deeper, offshore dives for food, while females and smaller individuals forage in the intertidal zones during low tide. Their laterally flattened tail functions as a powerful paddle for efficient, serpentine swimming. Strong, long claws enable them to grip slippery rocks both underwater, resisting strong currents, and on land.