Marine Science Chapters


The Effect of El Niño in Galapagos on the Marine Mammals and Reptiles

Most marine species are negatively impacted during El Niño, especially the marine mammals and reptiles. The changes in the marine environment, brought about by El Niño, are usually detrimental to the native species.

Galapagos sea lion in a tidepoolGalapagos sea lion and nursing baby
Galapagos sea lions are often found near the shoreline and in tidepools.
They give birth and nurse their young on the beach. (Halbach images)

Galapagos sea lions are endemic to Galapagos. The Galapagos sea lion is considered a subspecies of the California sea lion, Zalophus californicus, found only in the Galapagos Islands. Its scientific name is Zalophus californicus wollebaeki. These beautiful marine mammals feed on fish and invertebrates near the shorelines. During the '82/'83 El Niño most of the sea life died down to 70 to 100 feet deep. This was primarily because of the increase in water temperature (since most of these species live in cool water, they cannot survive when the water increases over five degrees above the norm). In some cases (mostly the plants), this death was also due to a lack of nutrients produced by the thermocline that developed at 70 to 100 feet.

Galapagos sea lion with pox
During the '82/'83 El Niño many of the Galapagos sea lions became diseased especially with sea lion pox (above). (SA image)

Galapagos sea lion with poxGalapagos sea lion bones
Even young animals were diseased and lethargic (left). A large number of Galapagos sea lions died by the end of 1983, leaving their bones on the beaches (right). (SA images)

El Niño disrupts the marine food chain and has adverse effects for many marine creatures. The loss of the plants and animals in the upper layer of the ocean changed the entire marine environment. Without the plants (seaweeds or phytoplankton), the herbivores starved; and without the herbivores, the carnivores starved. The small fish and invertebrates that were the normal food of the Galapagos sea lion were scarce during the '82/'83 El Niño and the sea lions became thin, weak, and diseased. Sea lion pox spread through the population and many died. Few babies were born that year as the sea lions had little energy except for bare survival.

Marine iguana colonyMarine iguana colony
Marine iguana colonies are usually common along Galapagos shorelines. (Halbach images)

Marine iguana headMarine iguana, brown color pattern
Marine iguanas are easy to approach and photograph. (SA images)

Marine iguana, green color patternMarine iguana, red color pattern
Marine iguanas come in a variety of color patterns. (SA images)

Marine Iguanas (Amblyrhynchus cristatus) are the only truly marine lizards in the world. This species lives in colonies near rocky shorelines where there is a lot of seaweed. They sun during the day to raise the temperature of their cold-blooded bodies, hanging out along the shorelines in large colonies.

Marine iguana in a 'normal' yearMarine iguana in the '82/'83 El Niño year
In normal years the shorelines of Galapagos are covered with marine algae (Halbach image left) but in severe El Niño years (like '82/'83) there is little algae (right). (SA image right)

Marine iguanas eat seaweed. Although they can graze on seaweeds living in the intertidal, there is not enough there for the entire colony. It is especially difficult in those long extreme El Niños where the Kelvin Wave has reached Galapagos and the sea level is up 4-5 feet, thus drowning the normal seaweed shoreline so the shorelines are bare.

Marine iguana eating on shorelineMarine iguana swimming away from shoreline
Marine iguanas may eat seaweed along the shoreline at low tide (left) or may swim away from the shoreline to feed at depth (right). (SA images)

Marine iguana swimming beyond the wavesMarine iguana diving
Marine iguanas swim out beyond the waves (left) then dive to the bottom (right). (SA images)

Most marine iguanas swim out to about 15 or 20 feet of water where they dive down to feed on subtidal seaweed. Their tail is laterally flattened and they use this to swim by waving it back and forth. They can hold their breath for thirty minutes or more. One record is a dive to 60 feet for over an hour.

Marine iguana feeding at depth

Marine iguana feeding at depth

Marine iguana feeding at depth
Marine iguana feeding on seaweed at about thirty feet deep in the ocean. (SA images)

The long toes help grasp the bottom when the marine iguanas are feeding. They can bite off large chunks of bottom seaweeds with their sharp jaws. During the '82/'83 El Niño most of the normal seaweed died, in the upper seventy feet, because of the increased ocean temperature and lack of nutrients. An opportunistic brown, filamentous alga that grew quickly on any available surface replaced it and this is what the marine iguanas were ingesting.

Dead marine iguanaDecomposing marine iguana
Dead marine iguanas were common in the '82/'83 El Niño (left). The shorelines, where marine iguana colonies lived, were littered with decomposing marine iguana bodies (right). (SA images)

This new alga could not be digested by the marine iguanas. It would pass through their digestive tract, giving them little nourishment. Many marine iguanas gave up their normal feeding behavior of diving and just stayed on the shoreline in '82/'83. Those that continued to swim out and dive were in very bad shape because they used a lot of energy to swim, dive, and feed underwater - without gaining any nutrition. During the '82/'83 El Niño between 55 and 70 percent of the marine iguanas died. There was no reproduction in most colonies that year and even the next year most of them were too weak to reproduce.

Healthy marine iguana colony in the '82/'83 El Niño year
Healthy marine iguana colony in the '82/'83 El Niño year surviving by a cold water seep. (GA image)

A few isolated areas were not affected by the temperature and nutrient change. These areas were where deep water would percolate to the surface from cracks in the volcanic islands. This deep water was cool and nutrient rich so the seaweeds in those areas thrived. There were a few such isolated areas in Galapagos in '82/'83 with healthy marine iguanas while the majority of the population was dying.

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(Revised 18 December 2004)
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