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What Do Marine Iguana Eat

Are you interested in learning more about the marine iguana?

Although marine iguanas cannot be kept in captivity as a pet, they are fascinating creatures to learn about.

One of their most unique features—their feeding habits—is what we’re exploring today.

So if you’ve been wondering what do marine iguanas eat, you’ve come to the right place! 

Marine iguanas subsist primarily on a diet of marine algae and seaweed found in the ocean. 

what do marine iguana eat

A Brief Intro to Marine Iguanas

Marine iguanas are unique from every other lizard on Earth.


They are the only lizards who spend time in the ocean.

We’ll find out more about why they spend time in the ocean later on, but first, let’s get better acquainted with these amazing reptiles.

The average adult male marine iguana is around 4.25′ feet in length, while females stay somewhere around the 2′ feet. length range.

Far from being the most attractive lizard in the tank, marine iguanas are typically black, have loose, scaly skin, long claws, and a squished looking face.

Different subspecies vary somewhat in size and color, though. 

Charles Darwin encountered and famously commented on marine iguanas during his voyage to the Galapagos Islands, describing the iguanas as “most disgusting, clumsy lizards,” and “hideous-looking.”

He may not have been great with compliments, though, who knows!

Where Do Marine Iguanas Live

Marine iguanas live only on the Galapagos Islands.

Populations of marine iguanas live on each Galapagos island.

Still, they’ve been isolated from each other for so long, and there are now unique subspecies of marine iguanas living on each island.

The various island’s subspecies of marine iguanas all have slightly different sizes, shapes, and colors.

What Threatens Marine Iguana’s Survival

Surprisingly, marine iguanas have no natural predators, so they are typically gentle creatures to encounter, making them popular with tourists.

However, though they have no natural predators, humans have introduced invasive species to the islands like feral dogs and cats, rats, pigs, and germs, which now feed on marine iguana’s eggs and prey on their young. 

Also, the marine iguana’s very specific habitat and their reliance on a single, unique food group further put them at risk of extinction.

So despite their highly adaptive capabilities, marine iguanas are in the endangered species category and have full protection on the Galapagos Islands. 

What Do Marine Iguanas Eat

Marine Iguana’s habitat on the Galapagos Islands plays a significant role in determining what (and how) they eat as a species.

As we stated earlier, marine iguanas live primarily on a diet of ocean algae and seaweed.

The marine algae grow on rocks near the island shores, meaning marine iguanas must swim and dive in the ocean to feed (more on this later). 

Nine different kinds of algae have been identified as marine iguana’s food, although they prefer to eat only 4-5 species of red algae found on the islands.

Only when the “good algae” isn’t available do marine iguanas add less favored species of algae to their diet. 

Although primarily feeding on algae, marine iguanas can eat other foods when necessary.

During times of food shortage, they have been known to feed on grasshoppers, sea lion afterbirth (yikes!), and crustaceans.

In the direst circumstances, they will resort to eating feces.

The droppings of sea lions, crabs, and even other marine iguanas are all fair game for survival. 

How Do Marine Iguanas Feed

We know marine iguanas feed on algae and seaweed growing on rocks in the ocean.

But how do they, a predominantly terrestrial (land-dwelling) reptile species, manage this feat?

The answer is, their bodies have adapted and evolved to accommodate their island life, so while other species of iguanas couldn’t survive if they were forced to feed in the ocean, marine iguanas are well suited for the task. 

For example, marine iguanas (unlike other iguana species) have very blunt snouts allowing them to better feed on rock algae underwater.

Also, their tails are much flatter than other iguana’s tails, helping them swim in a snake-like motion underwater.

Further, marine iguanas’ extra-long claws allow them to grip rocks on the ocean floor so they can hold themselves underwater for long periods during feeding.

Another unique feature supporting marine iguanas’ underwater feeding habits is their nasal salt gland.

When they feed underwater, marine iguanas ingest large amounts of saltwater.

To prevent dehydration, marine iguanas must expel the salt while still keeping the water in their bodies.

They do this by “sneezing” salt out of their special salt glands.

Essentially, the gland works by removing salt from their blood and pushing it out of their bodies through the nasal gland. 

How Do Marine Iguanas Survive During Food Shortages 

As we mentioned above, marine iguanas prefer to live on a diet of underwater algae, but in times of food shortages, they will eat other food sources to survive.

However, branching out to eat feces, sea lion afterbirth, grasshoppers, and crustaceans are not the only way marine iguanas survive food shortages.

They also have the unique ability to shrink in size! 

During climate events like El Nino, marine iguanas have been known to shrink in size by as much as 20%.

Why would they do this?

With little to no food available, the now smaller iguana requires far less food and can survive much longer on smaller amounts of food than they could before.

Remarkably, when the food supply is back to normal, marine iguanas quickly return to their original size. 


Marine iguanas are remarkable, highly adaptive lizards living primarily on a diet of marine algae and seaweed.

There are nine different kinds of ocean algae the marine iguana feeds on, although they prefer eating just 4-5 species of red algae.

Though ocean algae are their predominant source of food, during times of food shortages and climate events, marine iguanas are known to eat grasshoppers, crustaceans, animals after birth, and even feces.

Years of living on the Galapagos Islands have suited marine iguanas (predominantly terrestrial lizards), for underwater feeding.

They possess remarkable features like blunt noses, extra-long claws, flattened tails, and special salt glands to help them survive and thrive in an ocean environment.

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