Tag Archives: invasive species

When Restoration Is Eradication: Palmyra Atoll

On the Palmyra Atoll in the central Pacific Ocean, conservation biologists are in the midst of a massive, unprecedented experiment. They are trying to rid this remote island of all but a few coconut palms. The gangly tree is an icon of idyllic tropical islands, but also an aggressive invasive species that crowds out native plants and animals. By removing 99% of Palmyra’s millions of palms, biologists hope to create more room on the atoll’s three dozen islets for indigenous forests and seabirds, including the world’s second largest colony of red-footed boobies…

Red footed booby

Ripping out the palms has long been on the list of restoration projects on Palmyra. First, however, managers decided to attack another invader, black rats, which likely arrived on ships during World War II. With no predators, rats multiplied into the tens of thousands. They ate the seeds and gnawed the saplings of native trees and attacked seabird colonies, including those of sooty terns, which nest on the ground. Rats are the key suspects behind the absence on Palmyra of eight other species of ground or burrow-nesting birds, including shearwaters and petrels, all found on central Pacific islands that have remained rat-free. The first attempt to eradicate the rats in 2002 failed, partly because Palmyra’s abundant land crabs out-competed the rodents for the poisonous bait. The crabs’ physiology allowed them to eat the poison—the anticoagulant brodifacoum—without ill effect.

The second effort was successful only after [researchers] radio-collared rats and discovered that the rodents liked to hang out in the crowns of coconut palms. The crowns became a convenient platform for stashing cotton gauze sacks of poison bait, delivered by workers firing slingshots or dangling from helicopters. Crabs do not reach the palm tops.

Once rats were exterminated in 2011, researchers watched with delight as native tree saplings began to spring from the forest floor. There were also happy surprises. Scientists discovered two additional species of land crabs that had likely gone undetected because voracious rats suppressed their numbers. And researchers realized they were no longer being bitten by Asian tiger mosquitoes, a pest that attacks during the day and can carry dengue and yellow fever. It appears the mosquitoes depended on rats rather than humans or birds for blood meals…

Excerpts from Ridding Paradise of Palms, Science, Aug. 28, 2020, at 1047

Choked by Hyacinths: Lake Victoria

The report, Freshwater biodiversity in the Lake Victoria Basin (2018), assesses the global extinction risk of 651 freshwater species, including fishes, molluscs, dragonflies, crabs, shrimps and aquatic plants native to East Africa’s Lake Victoria Basin, finding that 20% of these are threatened with extinction. Of the freshwater species assessed, 204 are endemic to the Lake Victoria Basin and three-quarters (76%) of these endemics are at risk of extinction.

The African Lungfish (Protopterus aethiopicus), for example, is declining in the Lake Victoria Basin largely due to overfishing, poor fishing practices and environmental degradation as wetlands are converted to agricultural land. The lungfish is considered a delicacy for some local communities and is an important local medicinal product, used to boost the immune system and treat alcoholism. The lungfish is also traded at market, making it important to the local economy.

Lake Victoria is the world’s second largest freshwater lake by surface area. Its catchment area includes parts of Kenya, Tanzania, Uganda, Burundi and Rwanda. Also referred to as ‘Darwin’s Dreampond’, Lake Victoria is known for its high levels of unique biodiversity. The Lake Victoria Basin harbours immense natural resources including fisheries, forests, wetlands and rangelands….

Pollution from industrial and agricultural sources, over-harvesting of resources and land clearance are among the primary threats to biodiversity in this region. Invasive species also present an important threat to native biodiversity in the basin, affecting 31% of all species and 73% of threatened species. The purple flowered Water Hyacinth (Eichhornia crassipes) was accidentally introduced to Lake Victoria from South America in the 1980s, and at its peak covered close to 10% of the lake surface in dense floating mats. These mats reduce the oxygen and nutrient availability in the water column, which negatively affects native biodiversity. Opportunities for harvesting and exploiting the Water Hyacinth, for example by using the species as fuel in bio-digesters for energy production, are under investigation.

Excerpts from Livelihoods at risk as freshwater species in Africa’s largest lake face extinction – IUCN Report, IUCN Report, Apr. 30, 2018