Discovery Blog: Pioneering Cacti

While many Galapagos species are headline grabbers thanks to their adaptations and uniqueness, there are plenty of lesser heralded species to be found across the Islands that are just as special.

Step forward the three endemic cacti: the lava cactus, candelabra cactus and prickly pear cactus. For visitors to Galapagos, these three plants are such frequent sights that it can come as quite a surprise to find out that they are endemic and as unique to the Islands as the giant tortoises and flightless cormorants.

Surprisingly, there has been very little research into these cactus species since they were first described by Darwin during his visit in 1835. The great man actually sketched out some prickly pears in one of his many journals, but since then Galapagos’ cacti don’t seem to have grabbed the attention of scientists or visitors as much as some of the animals that rely on the cacti to survive.

As with all species of cactus, they are very well adapted to survive in arid environments. Able to store water in their juicy stems for months at a time, their leaves have evolved into spikes, reducing the amount of water lost through evapotranspiration and serving as a first defence against passing herbivores. They also have individual properties that allow them to thrive in the climate and landscape of Galapagos.

Competition, Lava Cactus ©Martin Whitaker

The lava cactus (Brachycereus nesioticus) plays a crucial role in the environment. All islands in the Galapagos Archipelago began life as lava that erupted from the numerous volcanoes which have formed as a result of the Galapagos hotspot. Once erupted, large lava fields would extend from all sides of a volcanic peak, forming some of the most inhospitable environments imaginable. The lava cactus however is ideally suited to these conditions and is often one of the first species to colonise fresh lava flows. Once these pioneer colonisers have a foothold on the environment, there begins a slow and gradual succession as the conditions are changed sufficiently to allow other plants to survive. Soil is created and larger trees and bushes can then begin to grow and form the green landscape that can be seen on many of Galapagos’ islands. Without the initial cactus pioneers, none of this would be possible and the Islands would be bare, highlighting the importance of these prickly plants.

Wildlife, Opuntia ©Vanessa Green

Prickly pear and candelabra cacti may not pioneer species, but the number of animals which rely on them make them a critical part of the habitat. Not only are they a source of water in the most intense droughts, but their fruits, flowers and even pollen are a major food source for a huge range of animals, from giant tortoises to carpenter bees. Their juicy stems are also able to provide food to those creatures clever enough to find a way past the spiked defence, such as mockingbirds. Even after death, the husky skeletons of both cacti often remain and provide excellent nesting sites for birds and invertebrates.

So while they may not be the most memorable of species for visitors to Galapagos, cacti play an incredible important role within the island ecosystem. Let’s hear it for the little (spiky) guys!

Which is your favourite lesser known species across the Islands? Let us know by emailing info@gct.org

by James Medland