The study reveals that nearly one in two wild plants on the island is not native to the territory
View of Isla del Coco in the eastern Pacific. (Beñat Orbea)
Located more than 500 kilometres off the coast of Costa Rica, Isla del Coco is a small island in the eastern Pacific Ocean known for its remarkable biodiversity and the high number of endemic species it hosts. Its uniqueness led to its designation as a UNESCO World Heritage Site in 1997, but it also makes the island particularly vulnerable: as in many oceanic islands, the introduction of non-native species represents one of the main threats to its ecosystems.
In this context, an international team led by researchers from the Botanical Institute of Barcelona (IBB, CSIC-CMCNB) Beñat Orbea and Jordi López-Pujol, with the participation of Neus Nualart (IBB), has recently published in the journal NeoBiota the first comprehensive catalogue of non-native plants on Isla del Coco.
Nearly half of the island’s wild flora is non-native
The study reveals that almost one in two wild plant species on Isla del Coco is not native to the island. Specifically, the researchers identified 89 alien species (45%), meaning species that arrived from elsewhere and are not native to the territory; 78 native species (39%); and 30 cryptogenic species (15%), whose origin cannot be determined with certainty.
According to the researchers, these figures —higher than previously thought— indicate that the island remains particularly vulnerable to new biological invasions.
“Our findings show a more concerning situation than previously assumed. However, we believe the island is still in an early stage of biological invasion, which makes it especially important to implement management measures in the short term. The positive side of this situation is that there is still room to act: if no action is taken, we could reach scenarios with many more alien species that would threaten the ecological stability of the island,” explains Orbea.
Urena lobata is one of the invasive plants on the island. It spreads quickly as its spiny seeds easily attach to animals. (Beñat Orbea)
An innovative method to classify plant species
To distinguish which plants are native and which have arrived from elsewhere, the researchers developed an expert decision tree. This method makes it possible to classify each species as native, alien or of uncertain origin in a transparent and replicable way, which is particularly important in a place where historical records are incomplete.
There is no permanent population on Isla del Coco, and information about its original flora is limited. Over the centuries, explorers, scientists and several attempts at cultivation have introduced different plant species, and today park rangers and researchers manage some areas with cultivated plants.
Nevertheless, the arrival of new plants from the mainland continues to pose a constant risk.
“The issue is not so much that some species are cultivated. For park rangers, having a small level of food security is important in case of emergencies, as the island is located very far from the mainland. The main problem is that the island lacks a biosecurity control system, which facilitates the introduction of new species. In this context, establishing white lists of authorised species could be a good management tool,” adds Orbea.
The importance of island biodiversity
Although islands cover only a small portion of the Earth’s surface, they host nearly one third of all known plant species, many of which are unique and found nowhere else in the world.
This concentration of unique species makes islands key hotspots for biodiversity and conservation. However, precisely because of their isolation and limited size, island ecosystems are particularly fragile: the arrival of plants from other regions can easily disrupt their natural balance.
For this reason, understanding which species are native and which have been introduced is essential for protecting remote islands such as Isla del Coco and preserving their biological richness.
Access to the study
The study, Cataloguing the alien spermatophyte flora of a remote tropical island: Methods and insights from Isla del Coco, Costa Rica, published in NeoBiota, is available here.