The marine iguana, a reptile found exclusively within the Galápagos Islands, is a unique evolutionary example. It is the only lizard globally that has adapted to a marine lifestyle, foraging in the ocean. These iconic creatures possess distinctive adaptations, such as specialized salt glands that allow them to expel excess salt ingested from their diet, often appearing as a “sneeze” of saline spray. Their flattened tails aid in swimming, while their dark scales help them absorb warmth from the sun after cold dives. Understanding marine iguana populations is important for Galápagos biodiversity.
Current Population Figures
Current estimates indicate the total population of marine iguanas across the Galápagos Islands is below 210,000 individuals. This species is classified as Vulnerable on the IUCN Red List, with an overall decreasing population trend. Population numbers are not uniform across the archipelago; they vary significantly by island and among the eleven recognized subspecies. For instance, Marchena Island is estimated to host between 4,000 and 10,000 marine iguanas, while Santa Fé Island supports a larger population of 15,000 to 30,000.
Obtaining precise population counts for these reptiles presents considerable challenges. Many marine iguana colonies inhabit remote, rugged, and often inaccessible coastal areas, making traditional ground-based surveys time-consuming and sometimes hazardous. To overcome these difficulties, researchers have increasingly adopted innovative methods, including drone technology for aerial imaging. The “Iguanas from Above” citizen science project further aids this effort, allowing volunteers to analyze drone footage and contribute to population assessments.
Marine iguana populations are also subject to significant natural fluctuations, notably influenced by periodic El Niño climatic events. During severe El Niño occurrences, warmer ocean temperatures lead to a drastic reduction in their primary algal food sources, causing mortality rates to reach as high as 90% on some islands. In response to such food shortages, marine iguanas exhibit a unique physiological adaptation, shrinking their body length by up to 20% to conserve energy. However, populations have shown a capacity to rebound quickly during subsequent La Niña periods when food becomes abundant again. Recent monitoring efforts at specific sites, such as Playa de los Perros on Santa Cruz Island, indicate stable and healthy populations, with more comprehensive estimates from ongoing drone surveys anticipated for publication in early 2026.
Pressures on Marine Iguanas
Marine iguanas face pressures from natural phenomena and human activities. El Niño events are a significant natural threat, causing ocean temperatures to rise and disrupting cold, nutrient-rich upwellings that support their primary algal food source. This leads to the disappearance of their preferred diet, often replaced by indigestible brown algae, resulting in widespread starvation. While a natural cycle, climate change is predicted to increase the frequency and intensity of these warming events.
Introduced non-native species also pose a severe threat to these ecologically naive reptiles. Feral cats, dogs, rats, and pigs prey on marine iguanas, especially vulnerable eggs and juveniles. Dogs can target adult iguanas, while rats and cats decimate hatchling survival rates on several islands, including Santa Cruz and San Cristóbal, hindering population recovery and long-term viability.
Pollution is another pressing concern for marine iguanas. Oil spills, even in trace amounts, have proven devastating; for example, the 2001 MV Jessica spill led to a 62% mortality rate in a Santa Fe colony, likely due to the oil killing essential gut bacteria needed for digestion. Additionally, plastic pollution, including microplastics and discarded fishing gear, risks ingestion and entanglement, with much of this debris arriving in Galápagos via ocean currents. Human presence, including tourism, can also induce chronic stress in iguanas and contribute to habitat degradation, particularly the loss of vital nesting areas due to infrastructure development.
Protecting Their Future
Conservation efforts safeguard marine iguanas and their unique Galápagos habitat. The Galápagos National Park and Marine Reserve play a central role, implementing strict regulations to protect these reptiles and their environment. This includes managing visitor access to sensitive areas and expanding marine protected zones, such as the 50% expansion announced in 2022, which aims to protect a significant portion of the region’s marine biodiversity.
Research and monitoring programs are also important for understanding and managing marine iguana populations. Projects like “Iguanas from Above” utilize drone technology and citizen science for comprehensive population counts and colony health assessment. Such initiatives also help identify areas most vulnerable to threats like plastic pollution, providing data to inform targeted conservation actions.
Controlling introduced species remains a high priority, with ongoing eradication programs targeting feral animals like goats and rats on various islands. Strict biosecurity measures and quarantine protocols prevent new invasive species introductions. These efforts are often collaborative, involving the Galápagos National Park Directorate, local communities, and international conservation organizations.
Public awareness campaigns educate residents and tourists about marine iguanas and their threats, promoting responsible behavior. Sustainable tourism practices encourage minimal wildlife disturbance and adherence to park guidelines. Broader climate change mitigation strategies for the Galápagos also enhance ecosystem resilience against increasing extreme weather events, indirectly benefiting marine iguana populations.