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Waging war on an alien invaderMonash researchers are leading the battle against the attack of crazy ants on a unique island ecosystem. STEPHEN LUNTZ and ALLISON HARDING report Remote Christmas Island in the Indian Ocean is world renowned for the spectacular annual migration of the red land crab and its unique native wildlife.
The ant, listed by the World Conservation Union as one of the world’s 100 worst invaders, is spreading through the 100 square kilometres of rainforest on the island, killing land crabs by the tens of millions and threatening other wildlife. It is a brutal death: the ants swarm on the crabs, spray them with formic acid and then devour them. The island forest is littered with crab corpses. Monash researchers from the School of Biological Sciences in the Faculty of Science first arrived on remote and isolated Christmas Island in 1986 to investigate its ecology. The Monash team was keen to study the island’s estimated 100 million crabs and the endangered Abbotts’ Booby, which nests in the rainforest canopy. But the team’s focus shifted rapidly from studying the unique island ecosystem to trying to save it, says Dr Dennis O’Dowd, director of Monash’s Centre for the Analyses and Management of Biological Invasions. “We must wage war on these invaders,” he says. “And if we are to save unique eco-systems, we need a strategic vision – and the resources to support our recommendations. “This ant invasion is serious stuff. The recently released action plan for Australian birds recommends that all of Christmas Island’s unique bird species now be reclassified as critically endangered – all due to the impact of the crazy ants.” The Christmas Island crabs are strictly forest dwellers and regulate almost everything that occurs in the forest, particularly the emergence of seedlings in the forest understorey. At the start of each wet season, millions of crabs hold extraordinary migrations from the rainforest and down steep cliff faces into the ocean to spawn. Months later, the baby crabs scuttle back up to re-inhabit the forests. On the Monash’s team arrival in the mid-1980s, it seemed red crabs formed a formidable barrier to would-be invaders. Dr O’Dowd, along with Dr Peter Green and Professor Sam Lake, documented the way the native crabs repelled invasions from Giant African land snails, a Central American tree and various weed species. The trio discovered crabs killed 97 per cent of snails in the rainforest within 48 hours, restricting the snails to the forest edges. But now crazy ant ‘supercolonies’ occupy more than a quarter of the Christmas Island rainforest, where they forage 24 hours a day on the forest floor and in the forest canopy, causing a chain reaction that completely alters the forest. Seedlings that were previously eaten by red crabs are now growing, converting the forest floor from an open understorey to a dense thicket. It is believed the invading crazy ants were inadvertently introduced to the island in cargo decades earlier. By 1997, the Monash team was recording a biological invasion of massive proportions. Dr O’Dowd believes the ants have so far killed about 30 million crabs. He believes the Monash research on the island over the past five years is developing into one of the world’s most comprehensive studies of a biological invasion – and the team’s work is now having results. Following recommendations from the Monash team, Parks Australia, responsible for managing the island rainforest, began investigating ways to control the crazy ants. Working with a pharmaceutical company, they developed a fishmeal bait with low concentrations of the ant poison Fipronil. The bait has been used during this year’s dry season. Foraging ants collect the bait and carry it to the nest, where it is passed among workers, larvae and, ultimately, to the queens. Initial reports are positive, and the ant control team has rolled back the invasion at three sites. The Monash team has also helped design a survey to investigate the ant population across the entire rainforest. The survey, overseen by Parks Australia, involves teams checking about 1000 points in the rainforest. The survey has already revealed three new infestations. At the same time, the Australian Research Council has funded Monash, in a partnership with Environment Australia, to continue its investigation of the invasion and its consequences. Two members of the Monash team, research fellow Dr Peter Green and postgraduate student Ms Kirsty Abbotts, are living on the island continuing the study. The Monash team has also been involved in outreach programs – giving community talks, assisting in the production of brochures (with text translated into Malay and Chinese for the some of the residents), and presenting information sessions to the 13,000 Christmas Island residents. The lessons learned on the island mean that the Monash team’s knowledge can also be used to battle other biological invaders in unique ecosystems around the world – including northern Queensland, where another crazy ant invasion has been detected this year. In fact, the same bait used on Christmas Island is being used in the war against the Queensland ants. “Whether or not our efforts to stem the tide of crazy ants on Christmas Island or elsewhere are successful, they improve our understanding of biological invasions and their means of prevention and control,” Dr O’Dowd says. “This becomes pivotal as globalisation spurs movement of species around the world and increases the rate of biological invasion.” ACTION: For more information about biological invasions as a global issue, visit www.issg.org or Monash’s Faculty of Science website at www.science.monash.edu.au |
But for the past few years, the island has been under siege. Its
status as a biological wonder of the world is being eaten away by a tiny
but nasty alien invader: the exotic crazy ant Anoplolepis gracilipes.