The Marine iguana (Amblyrhynchus cristatus) is a reptile belonging to the Iguanidae family found in the Galapagos Islands. This species is the only representative of the genus Amblyrhynchus and contains approximately twelve endemic subspecies distributed in this set of islands.
The marine iguana is currently classified as vulnerable according to the IUCN, due in large part to the pollution of its habitat and the decrease in its food resources. On the other hand, the El Niño phenomenon causes high mortality rates in this species (around 85%)..
After the effects of this phenomenon, it has been recorded that the body size of the marine iguana decreases by up to 20%, which is attributed to the scarce availability of food. In this way, iguanas show great adaptability to this type of natural event..
Marine iguanas feed almost exclusively on seaweed. Food search strategies depend on the state of ontogenetic development in which they are. In general, iguanas have two ways of feeding: either during low tide in the intertidal zone or in the subtidal zone, where these animals dive.
This species exhibits a competitive behavior for nesting sites, for which the females struggle to conserve territories with sandy substrates, ideal for digging and establishing their nests..
Some females search for empty burrows as a way to avoid competition and digging activities. During the nesting season, the females can move away from the coast about 3 kilometers until they find an ideal place for the nests..
Marine iguanas belonging to all size classes maintain a body temperature of between 35 and 37 ° C during the day. Despite this more or less constant temperature, the thermoregulatory behavior varies according to the age class..
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The body size of these animals tends to vary widely between populations and sexes. They are sexually dimorphic and the males reach sizes that exceed 100 cm, while the females usually measure approximately half of the male..
On the other hand, males have longer heads than females, while females have wider heads. In addition, they have a longer neck and larger spines..
Males, in some locations such as Fernandina Island, can reach up to 5 kg. However, on other islands where this species is found, they can reach a weight of 12 kilograms..
Animals weighing less than 500 grams are estimated to be immature. Adults usually reach a weight between 20 and 100 times greater than they present when hatching from the eggs.
These animals are generally black, although during the reproductive season the males may present a conspicuous grayish-reddish color on the sides and back. The female presents some coloration after copulation, but it is much more subtle than in the males..
These animals usually occupy intertidal, oceanic and neritic zones. The females can move up to a maximum of 2 kilometers from the coast, and the males are more commonly found in marine waters, being able to submerge up to 20 meters deep.
Marine iguanas occupy two types of territories, in resting territories, characterized by being rocky areas; individuals spend the night during periods of high tide and at night. During the day they occupy transitional territories, which are places of passage between feeding areas.
Amblyrhynchus cristatus It is an endemic species of the Galapagos Islands in Ecuador. The different subspecies are distributed in the islands of Fernandina, Isabela, Pinzón, Santa Cruz, Marchena, San Cristóbal, Wolf, Darwin, Roca Redonda, Santiago, Genovesa, Pinta, Santa Fe, Española, Rábida and other satellite islands..
Its current distribution is estimated at around 5000 kmtwo for the area of occurrence and less than 500 kmtwo for the actual occupancy area.
During the reproductive period, males significantly decrease their feeding activities, losing up to 26% of their body mass.
Males show a high degree of polygyny, that is, a male reproduces with a varied number of females during the reproductive season. Some observations indicate that a male copulates up to six times in a day with different females, with breaks of 12 minutes between events..
The females of A. cristatus they place the eggs in a synchronized way. This behavior helps to avoid the destruction of the nests by other females and in addition, the aggregation is a way to protect against some of their predators such as the Buteo galapagoensis.
The females are oviparous and can lay between one and six eggs in nests dug in the sand with a depth of between 30 and 80 centimeters. After laying the eggs, they frequently monitor them for about 10 days, although they do not stop feeding. They are subsequently left unattended, moving to other rest areas.
The incubation period is approximately 95 days. Marine iguanas hatch from eggs weighing between 48 and 65 grams. In the following video you can see how two specimens reproduce:
The iguanas A. cristatus They feed on seaweed, exhibiting a preference for some species of red algae. However, during high tide, when these algae are submerged out of reach of these animals, marine iguanas consume a greater proportion of the green algae. Ulva lobata.
The choice of food by these animals is influenced by morphology and size, as well as the nutritional properties that these foods provide. In addition, the abundance and availability of algae determines their consumption by marine iguanas..
Red algae (like Hypnea spinella) are high in protein and give iguanas greater amounts of energy than other species of algae such as brown algae (of the genus Hincksia) and green (of the genus Ulva).
For this reason, marine iguanas prefer red algae species, although in general they consume those that are more readily available. Feeding activities occur at any time of the day with a variable duration, spending up to 60% of the time on feeding activities.
The large individuals of A. cristatus that feed in the subtidal zone, they swim away from the coast up to 400 meters. In these areas they dive to feed on the algae on the seabed and each dive lasts an average of 175 seconds.
These feeding activities can be carried out daily or every two to three days..
On the other hand, some animals prefer the intertidal zone to feed. In these cases, individuals take advantage of the low tide to explore areas near the colony in search of algae that are exposed on the water. It is also common for them to dive into shallow wells formed in these areas..
Animals in the intertidal zones cool down while feeding, so they return to the resting zones to warm up again. This cycle is repeated until they are satisfied or, at least, the wave activity interferes in the search for algae..
Smaller animals, weighing less than 600 grams, prefer to explore cavities among lava rocks in search of small algae. In the following video you can see how a specimen feeds:
In marine iguanas, as in other reptiles, juvenile individuals require a higher energy intake than adults. Young animals consume four times more food in relation to their body mass than adults.
On the other hand, juvenile marine iguanas accelerate digestive processes by maintaining high body temperatures during the day. Despite having a faster metabolism than adults, they have the ability to obtain the same amount of protein as adults.
Marine iguanas are highly gregarious animals, being able to form colonies of up to 1000 individuals. These aggregations occur mainly due to the low pressure from predation, since on these islands there are no predatory mammals of greater importance for the species..
On the other hand, obtaining food requires a high energy cost, which encourages individuals to congregate near the feeding areas as a way to save energy in the movement between resting areas and foraging areas..
Males are highly territorial. This is observed to a greater extent a few months prior to the reproductive season, since male individuals of A. cristatus establish small territories.
Females show reproductive preferences for those males who establish their territories first. Because of this, it is common for males with central territories in the colony to have greater reproductive success than those who establish themselves in the periphery..
It is common for the latter to fight with the central males as a way to distract them and cause the spatial spread of the females to other territories..
Variations in thermoregulatory behavior reflect ontogenetic changes in feeding strategy, quantity and quality of food consumed, and predation pressures.
The animals sunbathe on the volcanic rocks of the islands, and thanks to their dark coloration they can quickly acquire high temperatures.
Generally, these individuals warm themselves as much as possible before starting a feeding activity, entering feeding zones with body temperatures of up to 43 ° C..
Smaller iguanas tend to lose heat more quickly, so they go out to rest areas more often. In these individuals, the basal temperature does not decrease to the same values as in larger individuals.
This is because smaller iguanas have greater difficulty swimming, so if their temperatures drop to the same levels as larger iguanas, they will have to spend more energy to return to rest areas..
In addition, being smaller and moving more slowly, they become vulnerable to predators..
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