A preliminary ecological risk assessment of the impact of tropical fire ants (Solenopsis geminata) on colonies of seabirds at Ashmore Reef

Department of the Environment and Heritage, 2007

Supervising Scientist Report 190
MG Bellio, P Bayliss, AJ Williams, R van Dam, GJ Fox & JH Moulden
Supervising Scientist
ISSN 1325 1554
ISBN-13: 978 1 921069 00 0
ISBN-10: 1 9210 6900 7

About the report

Ashmore Reef Nature Reserve, located within Australian Commonwealth waters off the coast of northern Western Australia (12°20'S, 123°0'E), is one of only three emergent oceanic reefs present within the north-eastern Indian Ocean (Figure 1). The Reserve, covering an area of approximately 583 square kilometres, was established by the Commonwealth in 1983 for the purpose of protecting its outstanding and representative marine ecosystems and for its overall high biological diversity, ecological and cultural values. Ashmore Reef provides important nesting sites for seabirds and turtles and supports a diverse range of species, including sea snakes, dugongs, and invertebrate fauna. Ecosystems of the Reserve are also recognised under international conventions and agreements, such as the Japan-Australia Migratory Bird Agreement (JAMBA) and the China-Australia Migratory Bird Agreement (CAMBA), and the Reserve has been designated to the List of Wetlands of International Importance under the Ramsar Convention since November 2002.

A recent survey carried out by the Northern Australia Quarantine Strategy (NAQS) (Curran 2003) identified that introduced marine and terrestrial species could pose a potential risk to the natural values and conservation objectives of the Reserve. As a result, the Department of the Environment and Heritage (DEH) commissioned the development of a 'Marine and Terrestrial Introduced Species Prevention and Management Strategy' for the Reserve (Russell et al 2004) and has since expressed its willingness to implement research and or monitoring to predict, assess and potentially minimise the impact of introduced species on the natural ecosystems of Ashmore Reef.

The present research project focused on gaining an initial understanding of the potential ecological risks and impacts of the introduced tropical fire ant (Solenopsis geminata) on the Ashmore Reef Nature Reserve, with particular attention to impacts on colonies of seabirds. The tropical fire ant is an introduced ant to all of the islands of Ashmore Reef, with its presence first recorded in 1992 (Curran 2003). Its presence was recognised by Russell et al (2004) as being a dangerous threat to ground nesting birds, and an assessment of the impacts was recommended as a matter of priority. It is a small aggressive ant, native to North America, which feeds on insects and other animals including vertebrates. Sick, vulnerable animals are particularly susceptible to attack, and as a consequence tropical fire ants may have the potential to hinder and deter nesting birds (in particular ground nesting birds), or even attack and kill hatching young and older surviving hatchlings (Drees 1994, Lockley 1995, Giuliano et al 1996, Pedersen et al 1996). The Ashmore islands are regarded as supporting some of the most important seabird rookeries on the North West Shelf. Large colonies of sooty terns, crested terns, bridled terns and common noddies breed on East and Middle Islands. Smaller breeding colonies of little egrets, eastern reef egrets, black noddies and possibly lesser noddies also occur on the islands (Commonwealth of Australia 2002). The impacts of tropical fire ants might also not be limited to birds; nesting turtles and others communities of native insects also might be affected (Russell et al 2004).

Therefore, the collection/collation of baseline information and the development of an approach/framework to predict or assess the likely extent of impacts of tropical fire ants will aid DEH priority-setting and management planning processes for Ashmore Reef. An initial step in any approach to assess and minimise/manage impacts of any invasive species should be an ecological risk assessment to identify key vulnerable species and key habitats, from which management actions can be guided and ongoing and new monitoring programs refined and developed, respectively.

In this report we present an ecological risk assessment framework and approach to predict the likely extent of impact of tropical fire ants on seabird colonies at Ashmore Reef.