The marine iguana, Amblyrhynchus cristatus, is a unique reptile found exclusively in the Galápagos Islands. It is the world’s only sea-going lizard, demonstrating an extraordinary adaptation to a marine existence.
Their Unique Algae-Based Diet
Marine iguanas primarily eat marine algae, or seaweed. They graze this vegetation directly from submerged rocks or during low tide when it becomes exposed. These iguanas show a preference for red and green algae, with at least 10 genera regularly consumed. In some populations, green algae such as Ulva might dominate their diet.
The specific types of algae consumed can vary based on factors like abundance, individual preference, foraging behavior, and the season. This specialized diet is notable for a reptile, as most other iguana species are terrestrial herbivores. While very rarely they may consume other items, their digestive system is specifically adapted for processing algae.
Anatomy for Aquatic Grazing
Marine iguanas have distinct physical features for consuming their marine diet. Their snouts are short and blunt, allowing them to press close against rocky surfaces. This flattened facial structure helps them to effectively scrape algae.
Their sharp, tricuspid teeth (each with three points) are suited for tearing and scraping the tough algal growth from rocks. These iguanas also exhibit a higher rate of tooth replacement compared to other iguana species. Strong, long claws provide a firm grip on slippery, wave-swept rocks, essential for stability while feeding in turbulent zones.
Foraging Strategies and Habitat
Marine iguanas use varied foraging strategies based on size and tidal conditions. Larger males typically dive into the ocean to graze on algae in deeper, cooler waters, sometimes reaching depths of up to 30 meters (98 feet) and remaining submerged for up to an hour. Females and smaller males, however, primarily forage in the intertidal zone, consuming algae exposed during low tide.
After foraging in cold ocean waters, marine iguanas bask on dark volcanic rocks to raise their body temperature. This thermoregulation is important for their metabolism and digestion. Their dark coloration helps them absorb solar radiation efficiently, allowing them to recover warmth before their next foraging trip.
Managing Salt Intake
Living in a saltwater environment, marine iguanas ingest significant salt. To manage this high salt intake, they have developed specialized cranial exocrine glands located above their eyes. These salt glands filter excess sodium chloride from their bloodstream.
The filtered, concentrated saline solution is expelled through their nostrils, a process often described as “sneezing.” This expulsion of salt helps maintain their osmotic balance, preventing dehydration and ensuring their survival in a marine habitat where freshwater is scarce. The expelled salt often dries on their heads, creating a white, encrusted appearance.