Amblyrhynchus cristatusMarine Iguana

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Geographic Range

The marine iguana inhabits the Galapagos Islands which form an archipelago off the coast of South America. The volcanic Galapagos has never been attached to another land mass so it is believed that iguanas rafted over water from South America (Cogger and Zweifel 1998). Some researchers believe that the land iguanas and the marine iguana diverged from a common ancestor at least 10 MY on the former islands of the archipelago which are now below sea level (Rassmann et. al. 1997).

Habitat

The marine iguana is found on the volcanic islands of the Galapagos. Many of the islands have steep rock cliffs, low rock ledges and intertidal flats. A. cristatus needs access to the ocean and a sandy area to lay eggs. They evolved in a habitat that is limited in predators. On Santa Fe an island in the Galapagos the predator are hawks, short-eared owls, snakes, hawk-fish, and crabs. With so few natural predators the marine iguana is very vulnerable to feral predators such as rats, dogs and cats. The feral animals can affect egg survival and adult mortality. Females are especially at risk of predation when going to the open nesting areas.

Physical Description

Amblyhynchus cristatus is a grey to black iguana with pyramid-shaped dorsal scales. They have shorter more blunt snouts than land iguanas, and they have a slightly laterally compressed tail. The young have a lighter color dorsal stripe (Rassmann et. al. 1997).

Reproduction

Males defend mating territories during the three-month annual breeding season. Females lay one to six eggs in burrows dug 30 to 80 cm deep. The eggs are laid in sand or volcanic ash up to 300m or more inland. Females guard the burrow for several days then leave the eggs to finish incubation, which is approximately 95 days. Nesting months are January through April depending on the island.

Lifespan/Longevity

Behavior

Amblyrhynchus cristatus faces a thermoregulation dilemma. The ocean waters that it relies on for food are very cold and since reptiles do not have the ability to regulate their body temperatures physiologically, they must bask in the sunlight to warm up. At low temperatures the ability of these animals to move effectively is reduced and they are vulnerable to predation. The marine iguana behaviorially compensates for its inability to move effectively. At low temperatures lizards are often highly aggressive, relying on less energetically expensive bluffs or bites than escape. The dark color of the marine iguana aids in heat reabsorbtion and males can change to full breeding dress for rapid re-warming (Cogger and Zweifel 1998). Hybridization between the Galapagos land and marine iguanas have been documented on Plaza Sur. DNA evidence suggests that hybridization is not common but possible (Rassmann et. al. 1997).

Food Habits

The marine iguana feed almost exclusively on marine algae (Cogger and Zweifel 1998). Larger members of the species feed more often by diving at high tide while smaller animals are restricted to intertidal feeding at low tide (Laurie and Brown II 1990). A major change in the marine algal flora occurred between November 1982 and July 1983. This coincided with abnormally high rainfall, sea level, and sea surface temperatures associated with El Nino-Southern Oscillation Event (ENSO). ENSO events are described as a mass of low-salinity nutrient-poor surface water moving south in the eastern tropical pacific. This causes a decrease in biological productivity and decreases survival and reproduction of animals dependant on the effected ecosystem. This was followed by unusually high mortality of maine iguanas (Laurie and Brown II 1990).

Economic Importance for Humans: Positive

The marine iguana does not affect humans because humans do not inhabit most of the islands they live on. The main food for the marine iguana is algae and that is not resource we compete for either.

Conservation Status

It is important to conserve the biodiversity of the marine iguana because it is a unique and interesting animal. It is necessary to protect their island refuges from feral pests and human exploitation because they are long lived animals that can not sustain added mortality.

Other Comments

The marine iguana has filled an interesting niche that no other living lizard does. It depends on the marine environment. To rid itself of the salt consumed while eating, A. cristatus excretes concentrated salt crystals from a nasal gland. The marine iguana regulates its body temperature by alternating from cold ocean water to basking on rocks near shore.

Contributors

Kristi Roy (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

References

Cogger, H., R. Zweifel. 1998. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press.

Indiviglio, F. 1997. Newts and Salamanders. Hauppauge, NY: Barron's Educational Series.

Laurie, W. 1990. Population Biology of Marine Iguanas I. Changes in Fecundity Related to a Population Crash. Journal of Animal Ecology, 59: 515-528.

Laurie, W., D. Brown. 1990. Phopulation Biology of Marine Iguanas III. Factors Affecting Survival. Journal of Animal Ecology, 59: 545-568.

Laurie, W., D. Brown. 1990. Population Biology of Marine Iguanas II. Changes in Annual Survival Rates and the Effects of Size, Sex, Age, and Fecundity in a Population Crash. Journal of Animal Ecology, 59: 529-544.

Rassmann, K., F. Trillmich, D. Tautz. 1997. Hybridization between the Galapagos land and marine iguana on Plaza Sur. Journal of Zoology London, 242: 729-739.