Cacti, iguanas and El Niño: How erratic weather is disturbing a fragile ecosystem on the Galápagos

Picture the Galápagos Islands and their charismatic wildlife bursts to mind: giant tortoises, sea lions, sharks and ‘Darwin’s finches’ – which first sparked the naturalist’s work on natural selection. 

But these animals aren’t just roaming around a barren outcrop of volcanic rocks. The Galápagos are home to an astonishing diversity of plants which underpin the wider ecosystem and are fascinating species in their own right.    

Like the finches, plants have adapted to different niches in the archipelago. Cacti, for example, have various spiky defences depending on their local predators.

The islands 1,000 kilometres off the coast of Ecuador have seven endemic genera, including lava cactus (Brachycereus) and Jasminocereus, a tree-like cactus, as well as a number of species of prickly pear cactus (Opuntia).

But these unique plants are under growing pressure from climate change and other manmade threats. 

“Plant restoration in the Galápagos is very important because plants are the base for food and habitat in ecosystems, and all living organisms on the island depend on plants for survival,” says Patricia Jaramillo, a senior researcher at the Charles Darwin Foundation. 

How is climate change impacting plant life in the Galápagos?

The ‘pioneer’ plants which first colonised the lava fields of the Galápagos are well-suited to arid conditions. But, by making rainfall more erratic, climate change is testing even their ability to cling on and regenerate.

In Baltra Island, for example, some plants have struggled to regenerate at their usual rate, despite the removal of invasive goats –  their nemesis for two centuries. 

“That would mean that today there are probably conditions we experience that are even more drastic than a few decades before,” says Nicolas Velasco, a researcher at the Charles Darwin Foundation (CDF). 

The Chilean scientist has spent two years in the Galápagos – one “super warm” and the latest surprisingly cold. Conversations with locals point to a recent trend of “hectic” weather.

Nicolas is involved in a scientific study into the phenology of plants – a discipline which looks at how the climate impacts plants’ natural cycles such as when they flower and fruit. Already, “it is very obvious that the phenology of endemic plants is changing,” he says.

Another phenological study focuses on the impact of El Niño. The natural weather phenomenon can bring heavy rains, which soften the soil and weaken the roots of plants like mature Opuntia echios, causing them to fall over.

On South Plaza island for example, an original population of 2,000 plants in the 1960s dwindled to around 400 individuals by 2014. Some scientists believe that climate change is making El Niño events stronger.

The delicate dance between cacti and iguanas

Walking along the strictly marked paths of South Plaza, amid a brilliant patchwork of foliage, yellow land iguanas basking in the sun are a common sight. 

Their population is finely attuned to reverberations in the ecosystem. The disappearance of the Galápagos Hawk here – a key natural predator – helped their numbers rise. But with the decline in Opuntia, competition for food has subsequently become fierce.

As part of CDF’s Galápagos Verde 2050 programme on ecological restoration, researchers have been planting cacti seedlings in one stretch of the island where their numbers collapsed.

“You have to be really quick with fencing, because within a couple of minutes iguanas arrive there and start to eat [the seedlings],” says Nicolas. “So that’s a way to see that they are really, really hungry.”

When I visit in July, our park guide is taken aback to see an iguana on the path with what appears to be blood around its mouth. The lizards are primarily herbivorous, but can also be opportunistic herbivores – eating carrion and ‘gaviotín’ (tern) chicks.

“Originally there was a good interconnection between the two species [land iguanas and cacti],” says Nicolas. “Iguanas usually eat the fruit of the cacti, so propagate the seeds.”

But in more turbulent climactic times, plants are coming under greater attack.

On Española island, for example, “super dry” conditions have led giant tortoises to eat prickly pear cacti for water, before the plant has time to produce seeds.

Under the water, land iguanas’ oceanic counterparts face a similarly variable situation. Marine iguanas suffer during strong El Niño events, as higher sea temperatures deplete seagrasses and other food sources.     

Water and other solutions on the Galápagos

With water scarcity a major threat to plant life on the remote Galápagos Islands, researchers have been trialling a range of tools under the CDF’s arid zone restoration project. 

One of these is called the Groasis Waterboxx. Developed by a Dutch flower exporter, the design acts like a kind of water battery around the plant, collecting rainwater and stopping it from immediately evaporating. The Sur Plaza seedlings have been fitted with these inside their cages.

Elsewhere, experts are laying down biochar or hydrogel in the soil. A form of charcoal, the former is mixed with the soil to improve it, enabling plants to access more nutrients. Hydrogel is a kind of white polymer which helps the soil retain more moisture. 

Plants can’t be helped with tech alone, of course. Restoration efforts are also deeply embedded in the social ecosystem of the islands. 

During its 2022 planting season on South Plaza, for example, each of the 220 plants required 20 litres of water, amounting to four cubic metres. 

Given the high costs of transporting water, CDF coordinates with tourist boats to bring water during their visits, relying on the support of the Galapagos National Park Directorate.

Thanks to these restoration efforts, South Plaza’s population of Opuntia has now rebounded to around 1,200 cacti, and natural regeneration by seed is picking up.

Tourists and locals will always have an impact on wildlife; directly trampling plants, unleashing invasive species like mice and rats, and altering habitats through construction.

So, crucially, organisations like the CDF are working with people to mitigate their impact. Santa Cruz residents, for example, are encouraged to grow endemic rather than ornamental plants in their gardens. 

Under the Galápagos Verde 2050 programme, the Charles Darwin Research Station holds an open house and works with school students to create ‘ecological gardens’, educating them about their home’s biodiverse heritage.

And for the international community who deva about giant tortoises and other Galápagos gems from afar, they stress that rewilding only works when plants are in the picture too.