The marine iguana, found exclusively in the Galápagos Islands, is the world’s only sea-going lizard. This unique reptile has adapted to forage for algae in the ocean. Its distinctive appearance includes a thick body, short limbs, and a row of spines along its back, complemented by a flattened tail for efficient swimming. These iguanas, which vary in color and size across different islands, spend significant time on rocky shores, basking to regulate their body temperature after cold ocean dives.
Natural Predators
Within their native Galápagos ecosystem, marine iguanas face predation primarily from specific bird and snake species. The Galápagos Hawk is a natural predator, targeting marine iguanas, especially vulnerable hatchlings and juveniles. These hawks can subdue adult iguanas, including nesting females, sometimes killing individuals weighing as much as or more than the hawk itself.
Galápagos Racer snakes also prey on marine iguana hatchlings and young. These non-venomous constrictors are active and agile hunters, effective at capturing smaller iguanas. While adult marine iguanas generally have fewer natural enemies, other native predators, such as short-eared owls, crabs, and even hawkfish, can pose a risk to smaller or less experienced individuals.
Threats from Introduced Species
Beyond their natural predators, marine iguanas face threats from species introduced to the Galápagos Islands by human activity. Feral cats, dogs, and rats endanger iguana populations. Feral dogs may prey on adult iguanas, while cats and rats typically target eggs and young hatchlings.
These introduced predators disrupt the natural balance of the ecosystem. Marine iguanas, having evolved in an environment with limited mammalian predators, lack effective defenses against these new threats. The presence of these non-native animals contributes to lower survival rates for marine iguana hatchlings on several islands.
Wider Environmental and Human Dangers
Marine iguanas also confront broader environmental and human-induced dangers that are not direct predation. Climate change, particularly intensified El Niño events, significantly impacts their food supply. During these events, warmer ocean temperatures cause preferred red and green algae to decline, replaced by brown algae that iguanas cannot easily digest or that may even be toxic. This food scarcity can lead to widespread starvation, causing marine iguana populations to decrease by as much as 90%.
Pollution represents another significant non-predatory threat. Oil spills have historically caused mortality, as seen during the 2001 MV Jessica spill, which reduced the Santa Fé population by almost two-thirds. Even minor oil exposure can be fatal, potentially by destroying the symbiotic gut bacteria marine iguanas rely on for digestion. Plastic pollution, including microplastics, introduces risks of ingestion and entanglement, while chemical pollutants can affect reproductive health.
Human presence and tourism also contribute to various dangers for marine iguanas. Increased human activity can lead to habitat degradation and elevate stress levels in the iguanas, with studies indicating higher stress-induced corticosterone in populations near tourist sites. The introduction of foreign pathogens by humans poses a significant threat, as the iguanas’ isolated evolutionary history means they lack immunity to many diseases. Accidental harm from human interactions and entanglement in fishing gear further endanger these reptiles.