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Some of Earth's weirdest creatures arise when a species goes where none of its relatives have gone before. When new islands form, the plants and animals that arrive on it have a unique opportunity to compete for niches that they would otherwise never have a chance at filling. In a place with moles or rodents, for example, a bat could never compete as a ground forager. New Zealand's lack of mammals, however, allowed bats to explore the forest floor, resulting in the incredible pekapeka. Volcanic islands make especially good homes for pioneering species like this, as they rise from the ocean with no connection to any mainland. This creates a sort of clean slate, and whatever animals or plants happen to show up will eventually adapt to develop a stable ecosystem. In the words of Aristotle, "nature abhors a vacuum" (this is also why nature is always covered in dirt).
Off the western coast of Ecuador in South America resides one of Earth's strangest and newest ecosystems, the Galapagos islands. This collection of 20 islands rose from the sea about five million years ago due to volcanic activity in the Pacific, and the creatures that colonized it quickly radiated to fill the brand new niches. One such species, a lizard, took a path that no other lizard had since the time of the dinosaurs. While its brethren colonized the land or debased themselves to become car insurance mascots, this lizard dove snout-first into the sea. Yet, it has begun to struggle due to the ways in which humans have modified the oceans, and this awesome lizard species is now at risk of extinction. Consider: the marine iguana, Amblyrhynchus cristatus.
Marine iguanas are, as the name suggests, iguanas, lizards of the taxonomic family Iguanidae (real creative, taxonomists). The species is divided into 11 subspecies, each of which inhabits their own island among the archipelago. They vary in length from the jumbo Amblyrhynchus cristatus hassi at 1063 mm (42 inches) to the fun-sized Amblyrhynchus cristatus jeffreysi at only 523 mm (21 inches) (poor Jeffrey). Besides their overall body size, marine iguana subspecies all look relatively the same, with short, blunted snouts, thick tails, and dark body coloration.
I love these iguanas, with their fancy dorsal frill, plump bodies, and strikingly-emotive faces (for lizards). Charles Darwin, however, did not like marine iguanas at all. During his time in the Galapagos, a place which played a crucial role in the formulation of his revolutionary Theory of Evolution, Darwin studied these iguanas and noted that they were on no uncertain terms the absolute butt-ugliest motherfuckers he had ever seen. In The Voyage of the Beagle, he wrote “It is a hideous-looking creature, of a dirty black colour, stupid, and sluggish in its movements.” In his personal journals from his time on the Beagle, he called them “most disgusting, clumsy lizards” and, most colorfully, “imps of darkness.”
Marine iguanas are Earth’s only ocean-dwelling lizards. They split their time between foraging at sea and soaking up rays on rocky beaches and cliffs, where they congregate in colonies numbering in the hundreds. Marine iguanas are herbivorous, consuming a mixture of red and green algaes that grow in the intertidal zones around their island homes. The pedantic among you might point out that algaes aren't actually plants and so you can't technically call marine iguanas "herbivores", but only the most fastidious of Reddit grammar Puritans would recognize the world “algivore”, so we will pretend that algaes are plants for now. Many animals can't digest algae due to its tough cell walls, but marine iguana guts contain symbiotic bacteria that aids in their digestion. These microbes cannot digest brown algaes, however (which incidentally are not even remotely related to green algaes, despite the similar name). Their adorable snubby snouts aid the iguanas in cropping algae clinging to rocky surfaces, while their powerful tails propel them through the water with surprising grace.
Other modern lizard species haven't adapted to a marine lifestyle for good reason: survival at sea presents a lot of challenges. For example, the ocean is much colder than land.As ectothermic (cold-blooded) animals, marine iguanas can't regulate their own body temperatures, so spending a lot of time in cold water puts them at risk of hypothermia (and also shrinkage, you'll see). To prevent this, the iguanas spend much of their time sunbathing and congregate in large groups to conserve body heat. Their dark coloration provides them an advantage here as well, as it helps them absorb extra heat from the sun. Despite these adaptations, marine iguanas can only withstand ocean temperatures for about ten minutes—any longer than that, and they won’t have the energy to make it back to shore. Upon returning from foraging, the normally laid-back marine iguanas often behave aggressively, hoping to intimidate potential predators into leaving them alone while they are cold and weak.
Salt, too, poses problems for marine iguanas. Most living things can only function with a specific range of salt concentrations in their bodies. Too much salt, and living tissues will dehydrate; too little salt, and cells will swell and burst from osmotic pressure.This is why drinking salt water can make you sick, and why saltwater fish generally can’t enter freshwater (except for bull sharks, which are far too angry to die). Marine iguanas’ food is saltier than the bottom corner of a bag of Tostitos, so they need to prevent themselves from getting salt-cured. Their solution? Sneeze it away. Marine iguanas have specialized glands in their nostrils which filter excess salt from their blood. Once enough concentrated salt has collected in these glands, they sneeze and blast it out. Some of this salt spray accumulates on the iguanas’ faces, giving them their distinctive white facial-markings (and here I thought they were just Juggalos).
Like all vertebrate animals, land or sea, marine iguanas must undertake the most arduous challenge of all—getting laid. Mating season begins around December and lasts throughout the winter. During this time, the largest male iguanas establish territories and compete with one another for female attention. Males attract this attention in two ways. Firstly, they perform vigorous head-bobs, which establish their fitness to females and the boundaries of their territory to rival males. While it may seem like the iguanas are just head banging to their favorite rock album (perhaps Limp Bizkit’s Chocolate Starfish and the Hotdog-Flavored Water), walking around doing your best impression of a bobblehead in an earthquake for three months actually costs a lot of energy. Like the ridiculously extravagant tail of a well-fed peacock, or a human male finally starting therapy, this strenuous behavior signals to females that a male would make a good mate. An additional perk of the bobbing behavior is that it ensures that the same iguanas don’t dominate the local mating scene every year, as it is so exhausting that the same male rarely succeeds at mating for consecutive breeding seasons.
Secondly, they turn colors. While normally black, male marine iguanas will become splotched with patches of vibrant reds and greens during the mating season. The iguanas don’t create these colors themselves, but instead obtain them via their diets, as algaes containing colored pigments tend to bloom in the months preceding the mating season. Since different Galapagos islands have different makeups of algal species, male breeding coloration varies between island populations and subspecies. Like the head-bobbing, these colors draw attention to particularly-large and desirable males, granting them larger territories and more females to mate with.
The normally-dark skin of male marine iguanas flush with brilliant reds and greens during the mating season. Different subspecies of marine iguanas take on different hues and patterns of coloration. Displayed here are A. cristatus wikelskii, A cristatus Venustissimus (often called “Christmas Iguanas”, presumably because they only come once a year), and A cristatus mertensi.
Quick note: the next image here contains a small amount of blood, so those who are sensitive to that may want to skip that one.
So if you’re a horny male iguana who doesn’t have a territory, how do you get your rocks off? There are several methods. Firstly, you can try to challenge a dominant male for his territory. Male marine iguanas fight each other via headbutting matches that can last up to five hours (sometimes with breaks so the combatants can take a lil nap). The iguanas have particularly thick skulls which allow them to partake in this headbutting without splitting their heads open (usually). But say you’re kind of a twink, without the impressive physique to take on a hunkier iguana and win. You can instead try sneaking. So-called “sneaker” males are small and weak, but manage to get access to a dominant male’s territory by pretending to be female. Once inside, they mate with some of the females and flee before the dominant male discovers the ruse. It's kind of like Mrs. Doubtfire, but with a lot more sex and a lot less family bonding. Not only is this a great trick for you lonely hearts out there, but it helps to increase genetic diversity in the marine iguana population, something vital to its success.
Lots of factors make life hard for marine iguanas, from cold ocean temperatures to the whole smashing each others’ brains into pulp, but another great challenge to their survival comes in the form of the capricious weather patterns of the Pacific Ocean. Readers in the Western Hemisphere have probably heard of El Niño and La Niña before in the context of weather, likely in the form of some arcane confluence of pressure systems and jet streams that serves as an excuse for why your local weather forecast ruined your weekend plans. These two weather patterns are perturbations in the trade winds that blow back and forth across the Pacific, and they have a ton of influence on the weather in the Americas. Both patterns can last from nine to twelve months, and they occur randomly every two to seven years. In addition to changing the weather, these patterns also control the distribution of warm and cold water across the Pacific, and as such they massively alter the conditions in marine iguana foraging grounds.
La Niña brings bounty to marine iguanas. This pattern pushes warm water westward towards Asia, allowing colder and more nutrient-rich waters to rise from deep in the ocean. This corresponds to a boom in algae and larger marine iguana populations. El Niño, however, brings doom. During El Niño, trans-Pacific trade winds weaken, causing warm water to flow East towards the Americas. This prevents nutrients from deep in the ocean from rising to the surface, causing a dieoff of the green and red algaes that marine iguanas eat, as well as a bloom of the brown algae that they can’t eat.
The truly catastrophic effects of El Niño on marine iguanas cannot be overstated. During this time, marine iguana populations drop drastically as the animals starve to death. One particularly-severe El Niño beginning in 1982 killed off 60 to 70% of marine iguanas on Santa Fe Island in six months, including 84% of juveniles. Despite how apocalyptic that sounds, marine iguanas have adapted to survive these times of extreme starvation. In response to El Niño, the iguanas shrink in length by up to 20% as they break down and metabolize their bones (I told you there would be shrinkage). While breeding practically ceases during El Niño, juveniles born in the wake of the event have been observed to achieve sexual maturity more quickly, allowing populations to recover.
That is where the story of marine iguana survival should end, but it doesn’t, because the greatest challenge to marine iguanas comes not in the form of seasonal weather patterns or horny headbutting, but in the ways humans have altered the planet. Marine iguanas are currently listed by the International Union for the Conservation of Nature (IUCN) as Vulnerable, but some subspecies such as the A cristatus Venustissimus (the Christmas iguanas) are listed as Endangered. A lot of human-centric factors have contributed to the decline in marine iguana populations. Invasive species such as rats, cats, dogs, and pigs often attack the iguanas and prey on juveniles. Under normal conditions 53% of juvenile marine iguanas survive long enough to reproduce, but colonies predated by feral cats can have a juvenile survival rate as low as 1%.
Pollution, too, has played a role in the decline of marine iguana populations. Large plastic objects such as fishing nets can entangle the iguanas, causing them to starve, suffocate, or drown. Algae can grow on plastic trash as well as rock or soil (as any owner of a fish tank can tell you), so marine iguanas may unintentionally ingest pieces of plastic as they forage. One recent study identified microplastics, tiny fibers or other debris that have broken off of larger plastic objects, in the feces of 98 out of 101 surveyed marine iguanas (what a thankless job, sorting iguana shit to find pieces of nylon). While too small to ensnare or suffocate, microplastics can cause a variety of health conditions in animals, such as diabetes, cancer, and hormonal disorders.
Most saliently, though, humans have made life worse for marine iguanas by changing the climate. As the burning of fossil fuels has warmed the planet, weather patterns worldwide have become more chaotic and often more serious. The World Meteorology Organization has predicted that the human-caused changes to our climate will cause El Niño to become more frequent and severe as the planet warms. While marine iguanas can recover from even severe El Niño events, researchers fear that more frequent El Niño conditions will be too much for the species to bear, leading to a population collapse.
I doubt I need to impress upon my readers the importance of actions taken to stop climate change: if you’re a climate change denier, Charles Koch’s blog is down the hall and to the right. But it bears mentioning that the effects of climate change are far-reaching and not always intuitive. If you asked the average person to tell you about the effects of climate change, they would probably cite hurricanes, wildfires, and droughts, not mass iguana starvation. But yet, the same process that has caused the cataclysmic wildfires of California and droughts in East Africa also has the potential to drive one of the most-unique species on the planet to extinction, as well as a host of other species with whom it shares its ecosystem. These animals, among thousands of others, are on the hook, suffering the consequences of our actions as a species.
So what can we do to help the marine iguana? On a large scale, we can work to create a more ecologically-responsible society. We can oppose the continued use of fossil fuels, change our diets and behaviors to support more sustainable industries, and work to develop new technologies such as renewable energy and carbon capture. We can also use the power we have as citizens to elect leaders who will hold corporations accountable for the damage they’ve done to our planet and support green legislation. Just by informing yourself on the true extent of the climate crisis, you are improving your ability to influence the world for the benefit of all species.
On an individual level, several conservation groups currently work to protect Galapagos species, the marine iguana chief among them. The International Iguana Foundation funds and conducts research to assess threats to marine iguana survival (they did the study with the microplastics in the lizard shit). The Galapagos Conservation Trust has developed several incredible projects to help protect marine iguanas and better understand the ecosystem of the Galapagos as a whole. Much of the Galapagos Conservation Trust’s work is done by citizen scientists, who the Trust trains to help further develop the scientific community in the Galapagos.
One project I’d like to specifically point out is Iguanas From Above, a citizen science program that you at home can directly contribute to. This project uses drones to capture footage of remote areas of the Galapagos where marine iguanas live but people do not. Citizen scientists like you and me are then tasked with going through the footage and counting the iguanas (much cooler than counting sheep). This data is used to establish more-accurate population records for the species and helps to inform scientists on how human activity in specific areas affects local marine iguana populations.
Marine iguanas are some of the weirdest animals on Earth. They are the only lizards on Earth who have taken to the sea, and they have developed some seriously unique adaptations to live that island beach bum life (rest in peace, Jimmy Buffett). But life is not all margaritas and cheeseburgers in paradise for these incredible lizards, and the consequences of human industrialism have threatened to destroy them. If the beauty and uniqueness of the marine iguana isn’t sufficient to convince you that it’s worth saving, consider that they have evolved to withstand and conquer many existential threats before. If we don’t act to save marine iguanas, their next evolutionary form might be less forgiving…
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Sources and More Information:
Charles Darwin University. "The Life of Charles Darwin." Charles Darwin University Australia.
Jones, Jen et al. "2019 Galápagos Marine Iguana Report." International Iguana Foundation, 2019.
MacLeod, A. et al. "Amblyrhynchus cristatus (errata version published in 2020)." The IUCN Red List of Threatened Species, 2020.
Mandujano, Carlos. "El Nino Spells Trouble for Vulnerable Galapagos Iguana." Phys.org, 5 July 2023.
Miralles, Aurelien, et al. "Shedding light on the Imps of Darkness: an integrative taxonomic revision of the Galápagos marine iguanas (genus Amblyrhynchus)." Zoological Journal of the Linnean Society, Volume 181, Issue 3, November 2017.
Rothman, Robert. "Galapagos Marine Iguanas." Rochester Institute of Technology
Roy, Kristi. "Amblyrhynchus cristatus." Animal Diversity Web, 2000.
Vasco, K., et al. "Characterization of the gut microbiome and resistome of Galapagos marine iguanas (Amblyrhynchus cristatus) from uninhabited islands." Anim Microbiome Volume 4, Issue 65 (2022).
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Consider Nature is written and published by Stephen Goralski. Editors for this article included Benjamin Gamble, Jesse Cristoforo, and Oli Platt. Our web designer is Oli Platt. Olmungandr, the Consider Nature logo, was made by Maxwell Schumacher.
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