Marine Science Chapters

2.2.2

The Effect of El Niño in Galapagos on the Terrestrial Environment

Tagus Cove in a 'normal' year Tagus Cove in an El Niño year
Tagus Cove (on the island of Isabella) is a favorite stop for Galapagos visitors because there is a picturesque crater near the cove as well as graffiti from the 1800s on the seacliffs. Normally there is little vegetation on the crater walls surrounding the standing water (left, Halbach photo) but during an El Niño there is a distinct 'greening' of the vegetation (right).

Terrestrial vegetation may thrive during El Niños because of the increase in rainfall. The normally desert environment can be transformed into a green and lush area where there are plants and/or seeds that can use this water. These plants seem to sprout out of nowhere with new species popping up.


Floreana hillside in a 'normal' year Floreana hillside in an El Niño year
Floreana hillside in a 'normal' year (left, Halbach photo) and in an El Niño year (right).

Undergrowth may flourish during an El Niño. Many plants sprouted during the '82/'83 El Niño that had never before been seen in Galapagos. Apparently the seeds had been there for some time but there had not been enough water for them to germinate.


Dune vegetation on Bartolome Pinnacle Rock on Bartolome
Dune vegetation on the island of Bartolome is generally scarce but during the '82/'83 El Niño it almost seemed to be taking over the beaches (left). Pinnacle Rock on Bartolome is shown on the right.

Sand dune vegetation increased during El Niño on the island of Bartolome. Bartolome has a lot of lava fields but one well-established sand dune environment near the white sandy beach and (often-photographed) monolithic volcanic spire called Pinnacle Rock.


Palo Santos trees in 'normal' year Palo Santos trees in a severe El Niño
Palo Santos trees in a 'normal' year (left, Halbach photo) and in a severe El Niño year (right).

Palo Santos (Bersera sp.) trees make hillside forests in Galapagos. They generally leaf out only during the rainy period (that is usually only during a three month period in normal years) and then drop their leaves for the rest of the year. During the extreme El Niño of '82/'83 the Palo Santos trees on the hillside of the island of Floreana leafed out again and again during the first six months of El Niño and then dropped their leaves and remained dormant until normal conditions returned in another year. It appeared they just ran out of energy to leaf out. The undergrowth in the Floreana forest continued to flourish during this severe El Niño.


Tree cactus in 'normal' year Tree cactus in an El Niño year
Tree cactus in a 'normal' year (left, Halbach photo) and in an El Niño year (right).

Tree cactus (Opuntia spp.) forests are common in Galapagos. These tree cactuses normally stand with little undergrowth and it is easy to walk through these tree cactus forests. During the '82/'83 El Niño the undergrowth increased so much that it was nearly impossible to walk among the tree cactuses.


Tree cactus and children Fallen tree cactus in the '82/'83 El Niño
Many of the older tree cactus plants are quite large especially when viewed with children for a scale (left). Fallen tree cactus plants were common in the severe '82/'83 El Niño year (right). Note the land iguana on the fallen tree cactus.

Many old tree cactus plants fell during the El Niño of '82/'83. These 200 to 300 year old cactus trees got too heavy with stored water. Normally cactus plants have very efficient water absorbing and storage adaptations. Most have shallow, fibrous root systems that soak up even the lightest rainfall and adaptations to hold the water for many months. These adaptations work great in desert areas like Galapagos with the normal six inches of yearly rainfall. But, when the rainfall increases, the tree cactus continues to absorb and store water. In 1982-83 some of the older cactus trees got so heavy that their root systems could no longer hold them and they toppled over.


Land iguana during 'normal' year Land iguana during the severe '82/'83 year
Land iguanas normally live in dry desert-like conditions (left, Halbach photo) but in El Niño years there is a lot of vegetation (right) on land.

Land iguanas (Conolophus spp.) feed on tree cactus pads. These terrestrial lizards often come running at the sound of a cactus pad hitting the ground. The lizards cannot climb the cactus tree so must wait for the occasional pad to fall. There is a lot of competition for these fallen pads in normal years, however in '82/'83 there were plentiful cactus pads on the ground from the fallen cactus trees and the land iguanas had enormous amounts of food.


Land iguana during 'normal' year Land iguana during the severe '82/'83 year
Land iguanas are normally slim and trim (left, Halbach photo) because food is scarce. During the severe '82/'83 El Niño they became quite fat with all the available food (right).

Fat land iguanas were common on Plazas Island in the summer of 1983 toward the end of the '82/'83 El Niño.

Galapagos giant tortoise
The Galapagos land tortoise is giant in the world of tortoises as you can see above.

Galapagos dome-shelled tortoise Galapagos dome-shelled tortoise eating
Dome shelled tortoises are common on many Galapagos islands (left) and are vegetatarians, feeding on plants and plant roots (right).

Galapagos tortoise during 'normal' year Galapagos tortoise during the severe '82/'83 year
Galapagos tortoises are normally relatively easy to see in Galapagos during normal years (left, Halbach photo) but during the severe El Niño of '82/'83 they were extremely hard to find as the vegetation covered them (right).

Galapagos is named for its giant land tortoises (Geochelone elephantopus). Many of the Galapagos Islands have their own type of giant land tortoise. The different types have varied shell shapes. Tortoises from wetter islands have dome-shaped shells and feed close to the ground. Tortoises from the drier islands have a raised front, (called saddleback shells), so that their necks can reach higher for the vegetation that they eat. During El Niño the giant tortoises were nearly impossible to see because of all the undergrowth.


Saddleback Galapagos tortoise
A saddleback Galapagos tortoise has its shell raised behind its neck, allowing it to reach vegetation further off the ground than its dome-shelled relatives.

Tortoises were removed by the thousands when pirates and whalers visited Galapagos during the 1500s - 1800s. These tortoises were packed in the holds of the boats, upside down, and kept there as a source of fresh meat for up to a year during the 1700s and 1800s. Some of the different types of tortoises are extinct now because of this and over-collecting by humans for zoos. Without native peoples in the Galapagos the plants and animals there had been undisturbed until their discovery in the 1500s. In the 1500s to 1800s there were few visits by humans except for occasional stops for food and water by pirates and whalers. The first settlements did not begin until around 1832.


Darwin's finch Darwin's finch Darwin's finch
Darwin's finches show remarkable variations between species.

Seed eating finches exhibited remarkable population increases during the '82/'83 El Niño. Darwin's finches are famous in the Galapagos as being one of the species that got Charles Darwin thinking about his Natural Selection and Evolution ideas in the mid 1800s during his voyage around the world. These are primarily seed eating birds. There are several species of Darwin's finches, generally they are referred to as six species of ground finches (Geospiza spp.), three species of tree finches (Camarhynchus spp.), one species of warbler finch (Certhidea olivacea), a vegetarian tree finch (Platyspiza crassirostris), a woodpecker finch (Cactospiza pallidus) and a mangrove finch (Cactospiza heliobates). The increased rainfall in severe El Niños not only causes the vegetation to grow more but seed plants generally make more seeds. Many of the finches had so much to eat during '82/'83 that they nested several times and produced 2-7 times the normal number of offspring. The population explosion was short-lived when normal conditions returned and many birds starved. But, during the El Niño it was definitely a remarkable event.



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(Revised 18 December 2004)
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