Marine Iguana

Marine Iguana
Conservation status
Vulnerable (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Squamata
Suborder:	Iguania
Family:	Iguanidae
Genus:	Amblyrhynchus
Species:	A. cristatus
Binomial name
Amblyrhynchus cristatus (Bell, 1825)

The Marine Iguana (Amblyrhynchus cristatus) is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The Iguana can dive over 30 ft (10 m) into the water. It has spread to all the islands in the archipelago, and is sometimes called the Galapagos Marine Iguana. It mainly lives on the rocky Galapagos shore, but can also be spotted in marshes and mangrove beaches.

Anatomy

Marine iguana swimming

On his visit to the islands, Charles Darwin was revolted by the animals' appearance, writing:

The black Lava rocks on the beach are frequented by large (2-3 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.^[2]

In fact, Amblyrhynchus cristatus is not always black; the young have a lighter coloured dorsal stripe, and some adult specimens are grey. The reason for the sombre tones is that the species must rapidly absorb heat to minimize the period of lethargy after emerging from the water. They feed almost exclusively on marine algae, expelling the excess salt from nasal glands while basking in the sun, and the coating of salt can make their faces appear white. In adult males, coloration varies with the season. Breeding-season adult males on the southern islands (Española, Floreana and nearby islets) are the most colorful and will acquire red and teal-green colors, while on Santa Cruz they are brick red and black, and on Fernandina they are brick red and dull greenish.

Another difference between the iguanas is size, which is different depending on the island the individual iguana inhabits. The iguanas living on the islands of Fernandina and Isabela (named for the famous rulers of Spain) are the largest found anywhere in the Galápagos. On the other end of the spectrum, the smallest iguanas are found on the island on Genovesa.

Adult males are up to 1.7 metres (5.6 ft) long, females 0.6–1 metre (2.0–3.3 ft), males weigh up to 1.5 kilograms (3.3 lb).

On land, the marine iguana is rather a clumsy animal, but in the water it is a graceful swimmer.

This is due to the traits it has that allow it to swim and make it different from other species of iguana; its laterally flattened tail and spiky dorsal fins allow it to swim further and faster, while its long, sharp claws allow it to hold onto rocks and other materials around it when there are strong currents so that it doesn't drown or get lost/too far away from land.

Its diet consists of seaweed and algae. To make it easier for it to get these, the marine iguana has a flat snout so that it can get closer to rocks that algae is growing on, as well as sharp teeth so that it can scrape off more of the algae. It has a special gland in its snout that filters its blood for excess salt that it may ingest while eating. It sneezes out the excess salt, which often leaves a salty crust around its nostrils, one of the aspects that made it unattractive to Charles Darwin.

Behavioural ecology

Highly colored individual of the Amblyrhynchus cristatus venustissimus subspecies found on Española Island

As an ectothermic animal, the marine iguana can spend only a limited time in the cold sea, where it dives for algae. However, by swimming only in the shallow waters around the island they are able to survive single dives of up to half an hour at depths of more than 15 m.^[3] After these dives, they return to their territory to bask in the sun and warm up again. When cold, the iguana is unable to move effectively, making them vulnerable to predation, so they become highly aggressive before heating up (since they are unable to run away they try to bite attackers in this state). During the breeding season, males become highly territorial. The males assemble large groups of females to mate with, and guard them against other male iguanas. However, at other times the species is only aggressive when cold.

Marine iguanas have also been found to change their size to adapt to varying food conditions. During El Niño conditions when the algae that the iguanas feed on was decreased for a period of two years, some were found to decrease their length by as much as 20%. When food conditions returned to normal, the iguanas returned to their pre-famine size. It is speculated that the bones of the iguanas actually shorten as a shrinkage of connective tissue could only account for a 10% length change.^[4] Current research accounts for the change in body size by arguing that marine iguanas can secrete a particular stress hormone that correlates with decreased skeletal size. ^[5]

El Niño events have also been noted to increase mortality rates and lower survival chances among larger-bodied iguanas. This is primarily because it takes the larger iguanas longer to warm up to make foraging trips and then reheat to digest the algae after emerging from the water. Consequently, smaller-bodied iguanas are at an advantages because it takes their body less time to warm up, allowing them to make multiple foraging trips and digest more efficiently. ^[6]

Evolutionary history

Researchers theorize that land and marine iguanas evolved from a common ancestor since arriving on the islands from South America, presumably by rafting.^[7][8] It is thought that the ancestral species inhabited a part of the volcanic archipelago that is now submerged.

Taxonomy and etymology

Its generic name, Amblyrhynchus, is a combination of two Greek words, Ambly- from Amblus (ἀμβλυ) meaning "blunt" and rhynchus (ρυγχος) meaning "snout". Its specific name is the Latin word cristatus meaning "crested," and refers to the low crest of spines along the animal's back.

Amblyrhynchus is a monotypic genus in that Amblyrhynchus cristatus is the only species which belongs to it at this point in time.

Conservation

This species is completely protected under the laws of Ecuador, and is listed under CITES Appendix II. El Niño effects cause periodic declines in population, with high mortality, and the marine iguana is threatened by predation by exotic species. The total population size is unknown, but is, according to IUCN, at least 50,000, and estimates from the Charles Darwin Research Station are in the hundreds of thousands.

The marine iguanas have not evolved to combat newer predators. Therefore, cats and dogs both eat the young iguanas and dogs will kill adults due to the iguanas' slow reflex times and tameness. Dogs are especially common around human settlements and can cause tremendous predation. Cats are also common in towns, but they also occur in numbers in remote areas where they take a toll on iguanas.

Gallery

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  A colourful adult male iguana.

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  Marine Iguanas, Galapagos Islands

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  Marine Iguanas, Galapagos Islands

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  Marine Iguanas, Fernandina, Galapagos Islands

See also

• Hybrid Iguana
• Zilla

Bibliography

• Rothman, Robert, Marine Iguana Galapagos Pages. Rochester Institute of Technology. Retrieved 19 April 2009.

References

1. ^ Nelson et al. (2004). Amblyrhynchus cristatus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006. Database entry includes justification for why this species is vulnerable
2. ^ Darwin, Charles (2001). Charles Darwin's Beagle Diary. London: Cambridge University Press. pp. 494. ISBN 0521003172 
3. ^ GalapagosPages says typical dives last only a few minutes at depths of less than five metres, but Darwin reported a member of the crew submerging an iguana for an hour, and pulling it out with a rope, still alive. IUCN says that adult males can be found in marine waters, down to depths of twenty metres.
4. ^ M, Wikelski; Thom, C. (Jan 6 2000). "Marine iguanas shrink to survive El Niño". Nature 403 (6765): 37–8. doi:10.1038/47396. PMID 10638740. 
5. ^ Wikelski, M. (2005). Evolution of body size in Galapagos marine iguanas. Proceedings: Biological Sciences, 272(1576), 1985-1993
6. ^ Wikelski, M. (2005). Evolution of body size in Galapagos marine iguanas. Proceedings: Biological Sciences, 272(1576), 1985-1993
7. ^ Rassman K, Tautz D, Trillmich F, Gliddon C (1997), The micro - evolution of the Galápagos marine iguana Amblyrhynchus cristatus assessed by nuclear and mitochondrial genetic analysis.: Molecular Ecology 6:437–452
8. ^ Marine Iguana: marinebio.org. Retrieved 16 August 2006.

External links

• Marine Iguana Podcast - Smithsonian Ocean Portal
• Images of Marine and Land Iguanas
• Iguanas of the Galapagos www.galapagosonline.com
• ARKive videos and slide show