I think it’s about time for a species from the Galapagos, that ecological wonder that everyone talks about. The Galapagos islands, if you don’t know, are a group of islands off the coast of Ecuador that are famous for their unique wildlife and because Charles Darwin visited them during his voyage on the Beagle. The islands are supposed to have helped Darwin formulate his theory of natural selection.
In any case, the Galapagos Islands are home to a rich variety of species, many of which are found nowhere else in the world. One of these is the marine iguana, the only lizard in the world that feeds in sea water. I know I said I was going to try and blog about more attractive reptiles, and although I think these guys are kind of cute, some people might not agree with me. For example, when Darwin first saw them, he had this to say:
‘The black Lava rocks on the beach are frequented by large (60–90 cm (2.0–3.0 ft)), disgusting clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. I call them ‘imps of darkness’. They assuredly well become the land they inhabit.’
Not exactly a glowing report, but I maintain that the marine iguana is a little cute. Here’s a picture to show you. Beautiful, right? He’s even got a mud bath going on to keep his skin silky smooth.
Marine iguanas differ in size depending on what island they inhabit; the largest are found on Fernandina and Isabela, where they can be up to 1.7 meters long. Though most of the iguanas are black, some colour differentiation occurs during the breeding season. This dark coloration helps the iguanas absorb as much light from the sun as possible, helping them warm up. This is especially important after the iguanas return from a watery foraging trip, as the cold water makes the animals sluggish.
Although not particularly adept swimmers, iguanas can dive for lengths of half an hour, and to depths of over 15 meters. Only the bigger iguanas actually dive however, the smaller bodied ones feed on less tasty seaweed exposed when the tide goes out. Small iguanas have difficulty in the water not only because they are weaker and so risk getting trapped by currents, but also because their littler bodies lose heat faster, making them unable to keep swimming.
For bigger iguanas, this is not such a big problem. They bask in the sun in the morning and generally go foraging at midday. They swim offshore and dive underwater to get to delicious seaweeds that grow on rocks. While feeding the iguanas use their strong legs and claws to grip rocks, to prevent them from being swept away by ocean currents.
Because they rely solely on seaweed for sustenance, marine iguanas are susceptible to fluctuations in seaweed levels. In particular, when El Niño cycles occur, seaweed levels drop and the iguanas can starve. But it has been found that these iguanas can change size, depending on how much food is available. During one El Niño event, some iguanas decreased their length by 20%. During this process, it’s likely that the iguana’s bones actually shrink, and that a stress hormone is responsible for this change. I think it would be pretty cool to be able to change size on command. Like Hank Pym, aka Ant-Man, that coolest of superheroes.
Marine iguanas have shown a remarkable ability to thrive in an environment most reptiles would have great difficulty living in. Hopefully we continue to preserve ecological treasures like the Galapagos so such unique creatures can continue to fascinate us.
Cover image By Jason Hollinger – Marine iguana, CC BY 2.0