GCT Ambassador, Henry Nicholls, takes a deep dive into the impacts of El Niño on the wildlife of Galapagos and the current work being done to monitor these impacts.
Henry Nicholls is a GCT Ambassador and editor of 'Galapagos Matters' magazine. He works as a secondary school teacher but has also spent many years as a freelance science journalist specialising in evolutionary biology, the environment, conservation and history of science. He has written two books about Galapagos, 'Lonesome George: The Life and Loves of a Conservation Icon' and 'The Galapagos: A Natural History'.
Imagine a globe. You place your hand on it and a deft left-to-right swipe sends it spinning on its vertical axis. With your eyes in line with the Equator, you watch as the familiar triangular shape of Latin America appears on the western horizon The vast Pacific Ocean comes into view and, with a smile, you recognise the cluster of enchanted islands we call Galapagos.
This Archipelago – as part of the Earth’s crust – completes an entire revolution (over 40,000 km at the Equator) in just 24 hours, so is travelling at a speed of around 460 metres per second. The waters that surround the Islands do their best to keep up, but as they are not tied to a tectonic plate, they get left behind. For the more rarefied air above the Islands, the challenge is harder still and it can’t even keep pace with the ocean.
These planetary truths account for the existence of the South Equatorial Current and the even more powerful Pacific trade winds, both of which are persistent in their East-to-West direction of travel. Appreciating these oceanographic and meteorological forces is crucial for understanding the unique ecosystem found in Galapagos and also the related phenomena of El Niño and La Niña
As warm surface water is whipped from the Eastern to the Western Pacific on the South Equatorial Current, it leaves something of a void in its wake. This pulls up water from the southern hemisphere on the powerful Humboldt Current. As much of this has been drawn from the cold depths, it carries with it the molecular remnants of long-perished organisms. These nutrients are the engine that
drives the marine ecosystem in Galapagos.
From the hot and humid environment of the tropics to below-zero conditions at the poles, climate patterns significantly impact us and our ecosystems. One such pattern is El Niño which occurs in the Pacific Ocean every two to seven years.
The marine producers like plankton, algae and seaweeds thrive, making food and habitats for larger communities of invertebrates, then fish, all the way up to the apex predators. The stability of this complex web of life depends entirely on the persistence and strength of the South Equatorial Current and the pull that this has on the cold, nutrient-rich Humboldt. In most years, this oceanic conveyor belt is pretty reliable, but every three to seven years – and for reasons that are many, complex and still poorly understood – the currents slow, stall completely or occasionally go into reverse.
In the 1600s, the Latin American fishermen who first noticed this phenomenon referred to it as El Niño de Navidad because it is particularly strong around Christmas time. Now we just call it El Niño for short
El Niño spells disaster for the marine ecosystem in Galapagos. Without the cold upwelling in the Eastern Pacific, the surface water in Galapagos warms from its normally cool 18°C to around 30°C, runs out of nutrients and much of the life that depends on it will die. Take the infamous 1982-83 El Niño, for example, one of the strongest and most devastating on record. Researchers documented massive levels of death throughout the marine ecosystem. Corals were bleached close to extinction, red and green algae vanished, resulting in the loss of 67% of marine iguanas in some colonies.
The Galapagos damselfish is thought to have gone forever, the penguin population crashed by 77%, all territorial male fur seals died, one-third of blue-footed boobies and two-thirds of Nazca boobies were lost, and so on, all in a matter of months.
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The intense pressure that El Niño places on those species that depend on the sea has resulted in some extraordinary adaptations. In the case of the marine iguanas, for instance, it appears that adults increase their chances of surviving an El Niño event by shrinking themselves, shortening the length of their skeleton by as much as 5cm. When the East-to-West currents pick up again, the waters cool and their favoured red and green algae return, and the iguanas grow back to their pre-El Niño length.
For the terrestrial ecosystem, the consequences of El Niño are dramatic too. In a normal year, when the warm surface water is carried off towards Asia, all the evaporation, the clouds and the rainfall occur in the Western Pacific. In an El Niño year, when the ocean currents have stalled, the clouds build in the Eastern Pacific and Galapagos typically experiences around ten times the rainfall. There is an explosion of vegetation, with knock-on positive effects all the way up the food chain.
In between successive El Niño events, the opposite phenomenon of La Niña may occur. Here, the trade winds and the South Equatorial Current quicken pace, resulting in more upwelling but less rainfall than normal. The upshot is an increase in marine productivity and a decrease in terrestrial productivity. So in reality, the Galapagos climate is in eternal oscillation, flip-flopping from El Niño at one extreme to La Niña at the other, with periods of relative stability in between.
On a planet experiencing rapid climate change, models predict the El Niño – Southern Oscillation is likely to increase in both frequency and severity. Life in Galapagos is tough enough as it is. For some species, more frequent and stronger El Niños and La Niñas may prove to be too much to survive.
The amazing diversity of wildlife in Galapagos is what makes the Archipelago so special.
In April, the Captain Darwin expedition arrived in the Galapagos Archipelago to document how the environment has changed since Darwin and to offer logistical support to local researchers. Andrea Varela and Denisse Dalgo, two Ecuadorians pursuing a doctoral degree by studying the emblematic Galapagos marine iguana – its population status and foraging ecology, respectively – joined the two-month expedition.
The timing could not be better to collect new data since there were signs that the Islands were in the midst of an El Niño event, with warmer waters reducing the algae coverage that makes up the marine iguana’s diet, posing a significant challenge to their survival and reproduction. Compared to El Niño events in the past, where some colonies of marine iguanas experienced up to 90% mortality, this year’s event seems to have been relatively mild. Based on preliminary analysis, small colonies suffered little or no mortality, whilst larger colonies may have lost more iguanas. In due course, we will be able to give more details on whether the iguanas changed their foraging pattern in response to the reduced availability of algae.
These data will be incorporated into the records that the Galapagos National Park Directorate is collecting to assess El Niño’s impact on the Galapagos ecosystem.
Discover more about the work being done to monitor marine iguana populations in Galapagos
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