![]() ![]() Large males defend territories for a short period, but smaller males have other breeding strategies. They mainly live in colonies on rocky shores where they bask after visiting the relatively cold water or intertidal zone, but can also be seen in marshes, mangrove swamps and beaches. Large males are able to dive to find this food source, while females and smaller males feed during low tide in the intertidal zone. Marine iguanas are the only extant lizard that spends time in a marine environment. Unique among modern lizards, it is a marine reptile that has the ability to forage in the sea for algae, which makes up almost all of its diet. The marine iguana ( Amblyrhynchus cristatus), also known as the sea iguana, saltwater iguana, or Galápagos marine iguana, is a species of iguana found only on the Galápagos Islands ( Ecuador). Fortunately, iguanas can increase their reproduction rate when population densities are low (such as after El Nino events), and thus can potentially recover from disasters to some extent (9). Scientists believe the oil may have killed the bacteria that the iguanas need to help digest algae, making it impossible for them to absorb nutrients (10). In the following year, around 15,000 iguanas on the Island of Santa Fe alone died over 60 percent of the entire island population. ![]() ![]() A recent oil spill from an Ecuadorian tanker in January 2001 spilled millions of litres of oil and fuel into the waters of the Galapagos Islands. Oil spills and marine pollution are also very serious threats as they destroy food reserves and the nesting beaches. The environmental fluctuations and the following invasion of an alga ( Giffordia mitchelliae) excluded the normal food species of the Galapagos marine iguana, causing the death of 50 percent of the population (8). On average, El Nino occurs every 12.3 years, although the 1982 to 1983 event was the most severe for around 100 years (2). This natural phenomenon is caused by a failing of the trade winds resulting in an increase in sea temperature of about 4.3 degrees Celsius along with an increase in sea levels and precipitation (2). This species is also sensitive to environmental fluctuations caused by El Nino (5). These feral animals eat iguanas and their eggs and have decimated hatchling populations in many colonies (1) (2). Galapagos marine iguanas have evolved anti-predator behaviours towards the native Galapagos Hawk ( Buteo galapagoensis) but are also threatened by introduced cats, dogs and rats. When the young hatch they look like and act like miniature adults, and have no parental care (7) ![]() Females often guard the burrows for several days then leave the eggs to finish incubation, which takes approximately 95 days. Females lay between one and six eggs up to 300 meters inland, in sand or volcanic ash burrows that are 30 to 80 centimetres deep. The nesting months are January through to April depending on the island (5). Careful not to waste energy, they rely on less energetically expensive bluffs or bites to protect their territory. Individuals breed normally just once every two years (9). This species breeds every year over a three month period, during which the males defend mating territories (4). Activity slows between noon and late evening, and before sunset the iguana retreats into crevices or beneath boulders for the night (2). They therefore excrete concentrated salt crystals from a nasal gland by sneezing (4). While feeding they also consume a great deal of salt solution which, in excess, can be toxic. They graze seaweeds in the shallow water around two to five metres in depth but can dive up to 25 metres down to rocks where there is an abundance of algae, and no competition from other iguanas (5). Larger individuals, however, do not lose as much heat and so they can be active for longer. Small individuals, which lose heat quickly, forage on rocks at low tide, scraping algae off the surface, and rarely dive into the sea. In fact, an iguana's size and the way it retains or loses heat determines its method of feeding. This forces them to return to the rocks and warm up in the sun again. The waters are extremely cold, and cause the iguana to lose heat rapidly when feeding. Only the largest five percent of individuals dive into the water for food, mostly during the hot midday hours (9). The vast majority of individuals in each colony feed almost exclusively on marine algae in the intertidal zones during low tide. Galapagos marine iguanas are active during the day and spend the first few hours after sunrise basking in the sun in preparation for activity. ![]()
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