The Marine Iguana – what makes it so unique?


Similarly to thousands of others across the UK on a Sunday night, I was encapsulated by David Attenborough’s new TV programme, Planet Earth II. It was an hour which spiked my curiosity about one reptile in particular, the Marine Iguana, endemic to the Galapagos Islands. It caused me to take a look at what makes these so special, and so different from land iguanas.

These animals are not the prettiest, scaled and ancient in their appearance, however they do have some amazing ecological adaptations, making them truly unique. Surprisingly, despite their scary appearance they are herbivores, feeding as the only sea going lizard in the world [2]. Living on land but feeding in the oceans, Marine Iguanas feed on seaweed and algae, diving up to 30m and holding their breath for around 45 minutes [4]. As this is a habit unique to Marine Iguanas, it provides them with an abundant food source, allowing them to thrive on the Galapagos Islands [2]. Interestingly, it tends to be the male iguanas who feed under the surface, with female and young iguanas feeding on the algae from rocks on shore [3] – something I find somewhat chivalrous.

The temperature of the waters around the Galapagos islands mean that Marine Iguanas can never spend too long in the ocean, returning back to the warm of land as they are ectothermic, meaning they cannot regulate their body temperature, unlike mammals and birds [3]. This makes them much more reliant on the temperatures of their environment, warming in the sun and cooling in the shade – when it is cold, they move slowly until they have warmed up enough to feed, and when it is hot they actually physically cover each other for shade. At night, when the temperatures of the Galapagos Islands drop considerably, they gather in vast numbers to conserve body heat [3]. The temperature endurance of an iguana is truly remarkable, when feeding then can lose up to 10˚C of their body temperature [3] – a change which, in humans, can be fatal. For these exceptional animals, they merely bask in the sun to warm up.

So what is it that makes Marine Iguanas so exclusive and adapted to their environment? It’s their long and muscular tail, which moves in a sinuous motion to act a propeller, pushing them through the ocean similarly to crocodiles [3] and razor sharp teeth to scrape algae off rocks. They also have tremendously sharp claws to help them cling to rocks on shore and underwater, withstanding heavy currents – another adaptation to help them feed. However the adaptations don’t stop there, due to the salty nature of the seas, they even have salt glands connected to their nostrils which clean their blood of extra salt accidentally ingested whilst feeding underwater [1].

Almost every shoreline of the Galapagos Islands is scattered with Marine Iguanas, but these mysterious creatures differ from island to island. Marine Iguanas show their exceptional colours as they mature, with coal black young maturing into red, black, green and grey iguanas [2]. The most colourful of these is the Española Marine Iguana, who have earned the nickname ‘ Christmas Iguanas’ due to their festive colours. Breeding season, which varies again from island to island also has an impact on the colourings of these reptiles, predominantly the males. During this time, the males develop red patches, on ‘Hood Island’ the male will turn completely red, in order to attract a mate and appear the most superior [3].

These entirely unique creatures, found in such a small part of our world have some amazing feeding adaptations and as the only sea going lizard in the world, every effort should be made to preserve their species and environment. I think their behaviour is truly remarkable.


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