One of Galapagos' most damaging invasive species, goats once ran rampant on Isabela Island. (Photo by Galapagos National Park Service)
Controlling invasive species was among the most pressing challenges identified by the World Heritage Committee when it recommended that Galapagos be placed on the list of World Heritage in Danger.
Scientists and conservationists agree that introduced plants and animals represent the single greatest threat to the terrestrial ecosystems of Galapagos. Since the discovery of Galapagos in 1535, humans have brought many alien species to the islands—some intentionally, including goats, pigs, cats, and both ornamental and food plants (vegetables and fruits), to name a few—while others, including rodents, insects, and weedy plants, have been carried to the islands accidentally.
The good news is that 95% of the archipelago’s native species remain intact today, due in large part to the islands’ remoteness and relatively recent discovery and settlement by humans. However, it is the islands’ isolation that makes the native plants and animals so vulnerable to new arrivals. Separated from many of the species on the continent, the native plant and animals species of Galapagos evolved and thrived in a world with little predation or competition.
While introduced species have been known to cause devastation to native flora and fauna throughout the world, and certainly in Galapagos, the threat from exotics in the marine environment is a more recent phenomenon and remains unstudied in Galapagos. The continuing increase in oceanic traffic, including increases in inter-island traffic related to Galapagos tourism, the number of cargo and other ships moving back and forth from the continent, the number of trans-oceanic and regional vessels using the waters around Galapagos, and the number of private vessels traveling through the islands, greatly increases the threat of hull and anchor transport of potentially invasive marine species. The successful establishment of introduced marine species elsewhere in the world has resulted in the complete restructuring of marine communities.
The number of introduced species in Galapagos continues to increase, with many of them impacting the native ecosystems.
A total of 36 vertebrate species have been introduced to Galapagos, with 30 of them becoming established, including 1 freshwater fish, 2 amphibians (frogs), 4 reptiles (all geckos), 10 birds, and 13 mammals. Most of the more invasive and devastating species are mammals, primarily goats, rats, cats, pigs, and dogs. The birds include domestic chickens and ducks, the semi-domestic Rock Pigeon, and wild species such as Smooth-billed Anis and Cattle Egrets.
Some 750 introduced plant species have been registered in Galapagos, with nearly 90% of them brought deliberately by humans for agricultural and ornamental purposes. The recent jump in the total number of introduced plants is more a result of increased interest in the problem coupled with more thorough surveys than of any exponential increase in the introduction rate. The majority of introduced plants are not overly invasive. The most invasive species are primarily found only on the inhabited islands and Santiago.
Approximately 543 alien insect species, more than 1/4 of the total insect fauna, have been registered in Galapagos. Most arrive in Galapagos on lumber, fruits and vegetables, and other organic material. The most serious threats to the Galapagos biota include two fire ant species (impact native invertebrates, reptiles, and birds), two wasp species (prey on native invertebrates and compete for food with finches), a scale insect (threatens many native plants), and an ectoparasitic fly (feeds on and harms nestlings of many bird species). Some of these also cause havoc for the human population.
While not yet a problem, the threat from the potential arrival and establishment of aggressive marine species, such as the north Pacific sea star Asterias amurensi and the barnacle Chthamalus proteus, among others, is cause for concern.
Efforts to combat invasive species
Since the establishment of the Galapagos National Park and the Charles Darwin Foundation (CDF) in 1959, efforts to control and eradicate invasive introduced species have been on-going. Initial efforts were primarily aimed at goat populations on the smaller islands and control of plants in the highlands of Santa Cruz. However, by the 1980s, the increase in tourism and the resident population made stopping any new introductions of equal importance.
The 1990s saw a major shift in invasive species work. The CDF played a lead role in establishing the Galapagos Inspection and Quarantine System (SICGAL), responsible for inspection of cargo from ships and planes, as well as the bags and luggage of tourists. Advances in eradication techniques worldwide provided the foundation for new and more expanded programs. Community education programs were implemented on the inhabited islands to increase both awareness of the threat from introduced species and participation by residents in the battle against invasives.
Biological control—the use of natural enemies to reduce the damage caused by pest populations—was first used in Galapagos beginning in 2002, to control the cottony cushion scale, which was threatening more than 60 native and endemic plant species. After six years of intensive research to determine probability of success and any potential impacts, the Australian ladybug, Rodolia cardinalis, was released. This was the first intentional introduction of an insect to Galapagos and it has proven effective at reducing the scale population to manageable levels.
The most dramatic success related to invasive species was achieved in March 2006, when Project Isabela—an unprecedented island restoration program in terms of size and scope—was completed, with the successful eradication of feral goats and donkeys from northern Isabela; goats, donkeys, and pigs from Santiago, and goats from Pinta.
Additional successes include the eradication of fire ants from Marchena, rock pigeons from Galapagos (were only established on Isabela, Santa Cruz, and San Cristóbal), cats from Baltra, and one species of blackberry from much of Santa Cruz, among others.
While the more aggressive invasive species continue to have major impacts on the ecosystems of Galapagos, as the level of human activity continues to increase, so does the threat of new introductions of potentially dangerous species. Current initiatives of the CDF, the GNPS, and other organizations in Galapagos to combat the problems of invasive species include:
Prevention and Awareness
Strengthen the inspection capabilities of the Galapagos Inspection and Quarantine System through improved training and equipment
Expand Community Monitoring Projects (CMPs) to achieve greater participation of the local population in identifying and responding to new invasive species
Strengthen education programs in schools and Environmental Education Centers
Complete goat eradications on the few remaining goat-inhabited islands based on the methodologies developed in Project Isabela: ultimate goal is a goat-free archipelago
Continue monitoring Judas goats on Santiago, Isabela, and other islands to detect any re-introductions
Complete eradication of feral goats, burros, pigs, and cattle already initiated on Floreana
Complete eradication of the freshwater fish Tilapia from El Junco Lake on San Cristóbal
Execute rodent eradications based on the results of an international workshop held in Galapagos in March 2007 – beginning with Seymour Norte, Rábida, and Pinzón
Continue humane sterilization programs for cats and dogs on inhabited islands
Complete inventory of introduced invertebrates present in urban and agricultural areas and their prioritization for management action
Complete feasibility studies for biological control options for introduced ants, wasps, and the mosquito that potentially carries West Nile Virus
Develop short- and long-term methodologies for control of parasitic flies and protection of their endangered host birds
Continue eradication attempts of fire ants on priority small islands and in smaller infestations on larger islands
Complete analysis of inventory of introduced plants in urban and agricultural zones on San Cristóbal (last island to be surveyed)
Initiate plant eradication projects based on the Weed Risk Assessment system
Eliminate select small populations of invasive plants
Develop a comprehensive management plan for the highly invasive Quinine tree with its large-scale eradication as the ultimate goal
Conduct feasibility studies of biological control options for the Lantana shrub, Mysore Raspberry, Quinine tree, and Guava shrub
Threat from Marine Invasives
Conduct diver surveys of hull epifauna and epiflora and of marine species associated with the Guayaquil port (most important port in terms of maritime transport to Galapagos)
Conduct a risk analysis of transport pathways from national and international ports
Develop risk assessment tools based on itineraries