Distribution and Biodiversity ofAustralian Tropical Marine Bioinvasions1

Marine invasions have been identified in virtually all regions of the world, yet relatively few introductions have been detected in the Tropics. This has been attributed at least in part to an increase in intrinsic native community resistance at lower latitudes resulting from strongly interacting food webs in high(er) diversity systems. However, recent evidence from surveys in Australia and elsewhere indicate that tropical systems are also susceptible to invasions, though detection ability may be constrained by taxonomic limitations. Preliminary analyses of data from surveys designed to detect introduced species do not support a pattern of decreased invasion success in higher diversity systems but do indicate a strong latitudinal gradient at the mesoscale of Australia. This cannot be attributed to disparities in search effort (controlled for by consistency in survey effort) or taxonomic knowledge. The original hypothesis of a decreased relative susceptibility of tropical versus temperate biota to invasions may remain viable, but be scale dependent. Additional confounding factors may include differing vector strengths and availability of source bioregions. THE INTENTIONAL AND accidental transport and introduction of marine species to new regions is currently perceived to be one of the primary threats to biological diversity (Hatcher et al. 1989, Lubchenco et al. 1991, Norse 1993, Suchanek 1994). Yet we currently do not have the necessary data to determine if the observed patterns of these introductions are a result of real differences between systems or merely reflect artifacts of sampling effort or identification ability. Marine (and estuarine) biological introductions have been detected in all oceans of the world (Pollard and Hutchings 1990a,b, Carlton 1996b, Ruiz et al. 1997, 2000, Hewitt et al. 1999), yet relatively few marine introductions 1 Paper presented at the Ninth International Coral Reef Symposium, Bali, Indonesia, 27 October 2000. Manuscript accepted 5 September 200I. 2 CSIRO Marine Research, Centre for Research on Introduced Marine Pests, GPO Box 1538, Hobart, Tasmania 7001, Australia (telephone: (+61 3) 6232 5102; fax: (+61 3) 6232 5485; E-mail: chad.hewitt:@marine.