Species Introductions and Potential for Marine Pest Invasions into Tropical Marine Communities, with Special Reference to the Indo-Pacific

Introductions of marine species by hull fouling or ballast water have occurred extensively in temperate areas, often with substantial deleterious impacts. However, current information suggests that marine introductions potentially able to achieve pest species status have been fewer in tropical regions. A 1997 risk assessment examining introductions to 12 tropical ports in Queensland (Australia) concluded that far fewer marine species appeared to have been introduced, even at major bulk export ports where the number of ship visits and volume of discharged ballast water are more than at most of Australia's cooler water ports. Results from recent surveys looking for introduced species in tropical ports across northern Australia are beginning to support this conclusion, although the lack of historic baseline surveys and the poor taxonomic status of many tropical groups are preventing a precise picture. The 1997 report also concluded that, apart from pathogens and parasites of warm-water species, the potential for marine pest invasions in Queensland tropical ports appeared to be low, and not only because much of the discharged ballast water originates from temperate ports in North Asia. In contrast, recent surveys of harbors in Hawai'i have found over 110 introduced species (including 23 cryptogenic species), the majority in the estuarine embayments of Pearl Harbor and O'ahu's commercial harbors. We suggest that the biogeographically isolated and less diverse marine communities of Hawaiian ports have been more susceptible to introductions than those of tropical Australia for several reasons, including the closeness of Australia to the central Indo-Pacific "triangle" of megadiversity (Indonesia- Philippines-Papua New Guinea) and consequent high biodiversity and low endemicity, hence offering fewer niches for nonindigenous species to become established. The isolated central Pacific position of Hawai'i and its long history of receiving worldwide commercial and naval shipping (including more heavily fouled vessels than contemporary merchant ships) is another key factor, although the estuarine warm-water ports of Townsville, Brisbane, and Darwin also provided anchorages for military units during World War II. Hull fouling remains an important vector, as it is the most likely cause of the recent transfer of the highly invasive Caribbean black-striped mussel (Mytilopsis sallei) to enclosed (lock-gate) marinas in Darwin by international cruising yachts arriving via the Panama Canal. The cost of eliminating this pest (>US$1.6 million) underscores the importance of managing not just commercial shipping but also pleasure craft, fishing boats, and naval ships as vectors of exotic species to ports, harbors, and marinas in coral reef areas.