Marine Iguana: where and when to see them

The marine iguana is an endemic Galápagos reptile whose feeding ecology is uniquely tied to marine algae. Ashore, its dark body, blunt face and spiny crest blend with volcanic rock. Size and breeding coloration vary among islands and populations. Although often conspicuous at accessible coastal sites, these iguanas face pressures from introduced predators, disease risks and ocean changes that can sharply reduce their food supply.

Size

60–120 cm total length

Weight

0.5–5 kg

Lifespan

Not reliably established

Status

Vulnerable

On land, marine iguanas bask to recover body heat, often forming dense resting groups on lava. They adjust posture and orientation to manage warming and cooling, and expel excess salt through nasal glands. Territorial males display with head movements and may fight during breeding. Females dig nests in suitable coastal soil, while smaller animals commonly feed on algae exposed along the intertidal shore at low tide. On land, marine iguanas bask to recover body heat, often forming dense resting groups on lava. They adjust posture and orientation to manage warming and cooling, and expel excess salt through nasal glands. Territorial males display with head movements and may fight during breeding. Females dig nests in suitable coastal soil, while smaller animals commonly feed on algae exposed along the intertidal shore at low tide. They are the only lizard in the world that forages in the sea, holding their breath for extended periods to graze underwater. After a cold foraging trip, they bask extensively to raise their body temperature back to optimal levels for digestion.

• It is the only living lizard specialized for feeding on marine algae.
• Nasal salt glands produce the conspicuous salty sneezes seen ashore.
• Some populations can temporarily shrink in body length during severe food shortages.
• Breeding males on certain islands develop vivid red and green coloration.

Shore observation is possible throughout the year at authorized Galápagos visitor sites. Warmer months can bring conspicuous breeding colors in some populations, but timing varies among islands. Tide, weather and the permitted itinerary often matter more for viewing than month alone. Shore observation is possible throughout the year at authorized Galápagos visitor sites. Warmer months can bring conspicuous breeding colors in some populations, but timing varies among islands. Tide, weather and the permitted itinerary often matter more for viewing than month alone. The breeding season typically runs from December to March, making these months ideal for observing courtship and territorial displays. Hatchlings usually emerge from their nests between April and June, offering a chance to see young iguanas.

Rocky volcanic shores with nearby algal feeding grounds are central habitat. Sandy or friable coastal patches provide nesting ground, and cracks offer shelter. Populations occur across much of the archipelago, but abundance, body size and local access differ greatly among islands. Rocky volcanic shores with nearby algal feeding grounds are central habitat. Sandy or friable coastal patches provide nesting ground, and cracks offer shelter. Populations occur across much of the archipelago, but abundance, body size and local access differ greatly among islands. The eastern islands of Española and Floreana, along with Santa Fe, host distinct subspecies, some of the smallest in the archipelago. Isabela and Fernandina support the largest populations and generally the largest individuals, favoring shores with extensive intertidal zones.

Marine algae dominate the diet, scraped from rock with specialized teeth and jaws. Red and green algae are especially important, with food composition varying locally. Warm-water events can replace nutritious algae with less suitable growth, causing severe food shortages and mortality. Marine algae dominate the diet, scraped from rock with specialized teeth and jaws. Red and green algae are especially important, with food composition varying locally. Warm-water events can replace nutritious algae with less suitable growth, causing severe food shortages and mortality. Juveniles and smaller individuals may consume detached algal fragments in tide pools or graze during low tide to avoid deeper water. Some individuals on smaller islands, where preferred algae are scarce, have been observed occasionally eating insect larvae or even land plants.

Common name

Marine Iguana

Scientific name

Amblyrhynchus cristatus

Animal group

Reptiles

Size

60–120 cm total length

Weight

0.5–5 kg

Lifespan

Not reliably established

Status

Vulnerable

Identification

Its blunt snout, flattened swimming tail and usually dark coloration distinguish it from the more yellowish Galápagos land iguanas with rounder tails. Its blunt snout, flattened swimming tail and usually dark coloration distinguish it from the more yellowish Galápagos land iguanas with rounder tails. Though typically dark, their coloration can vary from charcoal gray to reddish, green, or patchy shades, especially during breeding season. The presence of spiny dorsal crests, particularly prominent in adult males, also helps differentiate them.