Growing to approximately 3 ft in length these sea-going Iguanas exist only in the Galapagos Islands. Living on the black lava shore rocks they have developed into efficient swimmers feeding off shore mostly on marine algae and seaweed.
We traveled by taxi to a lava beach where these marine iguanas could be seen in great numbers swimming in the waters and basking on the lava rocks.
The cold waters of the Galapagos provide both the necessary food for the Marine Iguanas and its most deadly threats. The cold temperatures can immobilize an iguana if it remains in the water too long.
The marine iguanas once in water uses their specially adapted tail to dive at least 40 feet below sea level, where they will stay up to 30 minutes eating seaweeds before resurfacing. Before they dive they need to take some sun so they can increase their body temperature up to 97º F.
Once they dive into the ocean they grapple themselves to the bottom with their toes and graze the seaweeds that cover the rocky bottom. Because of the Humboldt's Current that flows to the north along the pacific coast line of South America the sea is amazingly cold.
As a consequence to the cold marine currents the iguanas could lose as much as 54º F of their body temperature in long time dives, so they will need another tanning session when they are back to the surface.
The Galapagos marine iguanas have developed some special glands of excretion of the salt to allow them to get rid of the excess of salt while they fed themselves under the water. These glands are visible when they "sneeze" as a excrete that expel the salt as a spray.
Until the arrival of man, Marine Iguanas only threats were that of larger fish and sharks encountered while swimming.
When Marine Iguanas are not feeding they seek safety and warmth of the land. In the 19th century when Charles Darwin visited the islands he found thousands of Marine Iguanas living along the rocky shore. He picked one up and threw it into the ocean it instantly swam back to the shore. This was repeated several times and the Iguana continued to seek the safety of the shore when it could have easily swum off to escape Darwin.
The black rocks under the equatorial sun provide needed warmth for the iguanas. On a warm day these rocks can heat up to deadly temperatures. Yet, territorial male Marine Iguanas, remain in the sun during the day. Cooled by a circulatory heat shunt carrying heat from the back to their bellies where the sea breezes coming off the cool ocean waters can cool them by convection. At night the iguanas pile by the hundreds in order to provide heat for one another.
Galapagos Land Iguana (Conolophus Subcristatus)
In 1835, when the HMS Beagle brought Charles Darwin to the Galapagos, there were so many land iguanas that the crews found it hard to find an open spot where to start a camping place, this because of the many iguanas that lived around. The introduction of some domestic animals caused a dramatic reduction of their population. The land iguanas in Santa Cruz, for example, were almost completely wiped out in the 1970s by wild dogs.
Land Iguanas grow to a bulky girth and 3 ft in length. Their yellowish-orange belly and brownish red back make them more colorful then their cousins the Marine Iguana. The Land Iguanas live in the arid portion of the islands.
Darwin was not much impressed with the land iguana:
"...they are ugly animals, of a yellowish orange beneath, and of a brownish-red colour above: from their low facial angle they have a singularly stupid appearance."
The mainstay of its diet is the Prickly Pear Cactus. They eat the pads and fruit including the spines. The cactus provides both food and water for the Land Iguanas can go without fresh water for a year. It is not unusual to see them sitting under a cactus, waiting for pieces to fall. They normally use their front feet to scrape the larger thorns from the pads, but they don't seem to mind the smaller thorns. Usually they will gulp down a cactus fruit in just a few swallows. Part of the adaptation to the drier environment includes a conservation of energy by slow movement. This makes the animals seem lazy or stupid. Land Iguanas burrow into the ground creating tunnels which provides a place for nesting, shade during the day and protection at night.
We saw these land Iguanas at the Charles Darwin Center that was on the island of Santa Cruz. We took a 2 hour speedboat/ferry from San Cristobal as a day trip and visited several interesting spots.
Tom
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