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Galapagos Islands-258 | by Tristan27
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Galapagos Islands-258

A Marine Iguana "spitting" at a Sally Lightfoot Crab on the rocks on Santa Cruz Island. The "spitting" action is actually just the Marine Iguana's way of excreting the salt from the sea water and is not (despite what it looks like" an attack or defence mechanism - this was just a coincidence!


Marine Iguana

The Marine Iguana (Amblyrhynchus cristatus) is an iguana found only on the Galapagos Islands that has the ability, unique among modern lizards, to live and forage in the sea. 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. 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.” 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 are the most colorful and will acquire reddish 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 approximately 1.3 m long, females 0.6 m, males weigh up to 1.5 kg. On land, the marine iguana is rather a clumsy animal, but in the water it is a graceful swimmer, using its powerful tail to propel itself. As an exothermic 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. 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 scarce 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. Researchers theorize that land and marine iguanas evolved from a common ancestor since arriving on the islands from South America, presumably by driftwood. It is thought that the ancestral species inhabited a part of the volcanic archipelago that is now submerged. A second school of thought holds that the Marine iguana may have evolved from a now extinct family of seagoing reptiles. Its generic name, Amblyrhynchus, is a combination of two Greek words, Ambly- from Amblus meaning "blunt" and rhynchus 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. This species is completely protected under the laws of Ecuador. 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 eat both 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.


Sally Lightfoot Crab

The crab Grapsus grapsus (known variously as "red rock crab", "abuete negro", and, as "Sally Lightfoot") is one of the most common crabs along the western coast of South America. It can also be seen along the entire coast of Central America and Mexico, and nearby islands. It is one of the many charismatic species that inhabits the Galápagos Islands, and is often seen in photos of the archipelago, sometimes sharing the seaside rocks with the marine iguanas. The Sally Lightfoot is a typically-shaped crab, with five pairs of legs, the front two bearing small, blocky, symmetrical chelae. The other legs are broad and flat, with only the tips touching the substrate. The crab's round, flat carapace is just over 8 cm (3 inches) in length. Young Sally Lightfoot’s are black or dark brown in color and camouflage well on the black lava coasts of volcanic islands. Adults are quite variable in color. Some are muted brownish-red, some mottled or spotted brown, pink, or yellow. Sally Lightfoot crabs are thought to have been named for a sultry nightclub dancer from Guayaquil, whose alluring performances in her red and yellow dress, captivated 19th century sailors. This crab lives amongst the rocks at the often turbulent, windy shore, just above the limit of the seaspray. It feeds on algae primarily, sometimes sampling plant matter and dead animals. It is a quick-moving and agile crab, and hard to catch, but not considered very edible by humans. It is used as bait by fishermen.


Santa Cruz

With the largest human population in the Galapagos archipelago, Isla Santa Cruz is the most important of the Galapagos Islands. Meaning Holy Cross in Spanish, this island is also known as Indefatigable, after the HMS Indefatigable landed here long ago. The second largest island terms of land area at 986 sq km, Isla Santa Cruz is home to the key town of Puerto Ayora, the Charles Darwin Research Station and the headquarters of the Galapagos National Park Service. With its own airport on Isla Baltra a few miles away, Isla Santa Cruz is where most visitors who come to the Galapagos Islands usually stay. With a number of bars, hotels, restaurants and shops in Puerto Ayora, most tours of the Archipelago also usually begin from here.


Galapagos Islands

The Galápagos Islands (official name: Archipiélago de Colón; other Spanish names: Islas de Colón or Islas Galápagos) are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, some 900 km west of Ecuador. It is a UNESCO World Heritage site: wildlife is its most notable feature. Because of the only very recent arrival of man the majority of the wildlife has no fear of humans and will allow visitors to walk right up them, often having to step over Iguanas or Sea Lions.The Galápagos islands and its surrounding waters are part of a province, a national park, and a biological marine reserve. The principal language on the islands is Spanish. The islands have a population of around 40,000, which is a 40-fold expansion in 50 years. The islands are geologically young and famed for their vast number of endemic species, which were studied by Charles Darwin during the voyage of the Beagle. His observations and collections contributed to the inception of Darwin's theory of evolution by natural selection.

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Taken on April 19, 2009