Sunday 4 November 2012

Marine Iguana

Image: lgooch via Flickr
Amblyrhynchus cristatus
Just imagine. There you are in warm, equatorial South America, munching on your luscious greens as you rest in the hot, moist air. A storm wanders by. It picks up the very branches on which you sit and casts them into the sea. You drift on your accidental raft for a long time, not knowing if you'll ever see land again.

One day you spy something in the distance, a hazy mound of land, far away. As you get closer it looks like a big, black rock. You get closer still and it looks like a big, black rock, only more craggy. Finally, you come aground. You look around at the post-apocalyptic landscape...

Image: Derek Keats via Flickr
Things aren't looking good for a cold-blooded vegetarian.

Image: Derek Keats via Flickr
You wonder how you can possibly make a life here.

And yet that's exactly what the Marine Iguana did. Plucked from their home in South America by the vagaries of the weather, abandoned on the volcanic Galápagos Islands at the whim of the currents, the Marine Iguana had to adapt to survive. And boy did they do so!

Image: A. Davey via Flickr
The Marine Iguana is the only lizard in the world to make its living in the sea. Most of their relatives are completely tied to land, with some spending time in lakes or rivers. The Marine Iguana is alone in foraging for its food in salt water.

Only the biggest of Marine Iguanas can afford to dive right into the sea and swim around in search of algae and seaweed. The water is cold, so smaller individuals would become lethargic and slow far too quickly to make such ventures worth the risk. They usually stay around the intertidal zone, tearing at the algae covered rocks when the tide is low, aided by their flat snout and sharp teeth. They don't get to chomp on juicy leaves like land iguanas, it's more like picking the last specks of meat from a chicken bone.

Image: putneymark via Flickr
The big fellows can get up to 1.7 metres (5.6 ft) long and usually dive for just a few minutes at a time and prefer to remain at depths of less than 5 metres (16.5 ft). Their tail is flattened to power them through the water, while the long spines on their back act as a kind of dorsal fin.

They take in huge amounts of salt as they feed, which could easily build up to dangerous, toxic levels. To deal with this they have a special nasal gland which filters out the salt from their blood so it can be released through their nostrils. In other words, they sneeze it out. With some force.

So, after foraging in the sea it's time to head to land, warm up and digest their hard earned meal. Loads of them lounge around the rocks in an intimate orgy of relaxation. Long toes and claws secure them against the waves, black scales efficiently absorb heat while their nostrils are periodically aflame with salty bogies that can actually get encrusted on their face, marking them with white patches that denote the extraordinary lengths they've had to go to in this bleak wasteland.

Image: lgooch via Flickr
The Marine Iguana has been remarkably successful, spreading to all the islands of the Galápagos archipelago and dividing into 7 subspecies distinguishable by colour and size. They seem to have a remarkable air of self satisfaction as they bask in the sun, even if their smug facial expression is topped with bumps and spikes even more prehistoric and treacherous than the surrounding landscape.

Image: Seven Bedard via Flickr
And then comes El Niño with all the chaotic, sort-of-predictability of a financial crash. And just like most economic crises, it's great for some, disastrous for others.

El Niño in the Galápagos Islands is marked by more rain and warmer temperatures on land and sea. It's wonderful for terrestrial plants, but it means that cold, nutrient-rich water doesn't rise up from the depths to nourish the shallows. Fish and sea birds have a tough time, and so does our own Marine Iguana as its supply of algae and seaweed falls.

Many Marine Iguanas die at this time, particularly the large ones who require the most food and take the most time to warm up before they can go foraging again. But they have a trick up their scaly sleeve. They can shrink! Marine Iguanas have been seen to lose up to 20% of their body length during these stressful conditions. It's thought their actual bones get shorter! And when conditions improve they can return to their usual length.

Image: Benjamint444
Colourful male in full breeding season garb
Come the breeding season, males acquire a bit of fire in their flanks. Manly Marine Iguanas of the southern islands are the most colourful, going from "volcanic rock black" to "lava flow red". Others are more subtle and some even acquire tinges and splodges of green as if in remembrance of their ancestors.

Image: Wikipedia
Greenish male, snoozing
Females don't get all fashion concious, they have too much work to do. They may travel over 300 m (985 ft) inland to dig a nest in sand or volcanic ash. Here, they lay up to six eggs which they defend for a few days before leaving. The eggs won't hatch for another 3 months.

Image: Dallas Krentzel via Flickr
The hatchlings look a lot like their parents, just a little less craggy and spiky. Then again...

Isn't that always the way?


  1. wow! they are so cool! living dragons.

  2. Yes! It's remarkable how dragony they look!

  3. That guy near the bottom has the right idea. I could go for an iguana-snooze right about now.

  4. Such amazing creatures! When I was in grad school, another lab in the dept was studying stress responses in marine iguanas during those sorts of events (see the Romera lab for more:

  5. @Crunchy: Snoozing is pretty much always a great idea, and Marine Iguanas are masters of the art!

    @Olivia V. Ambrogio: That's fascinating! I hadn't thought of that: if they shrink during an El Nino then would they do something similar in after oil spill?

  6. Handsome and the swim! Any relation to Michael Phelps? Just kidding. Yes, a wonderful story of evolution.Sink or swim so to speak.

  7. Ha! They're certainly very impressive in the water!

  8. One of my favorite bits of trivia about these guys - they gave Charles Darwin the CREEPS! He actually uses the words "imps of darkness" in his earliest written descriptions of them.

  9. I saw that! I think I was meant to mention that somewhere but I must have forgotten. Whoops!

    It's no surprise he found them so creepy. Even their lips look like black teeth on a skull!