Invasive marine species (IMS) are thought to be one of the most serious anthropogenic threats to global marine biodiversity. There are numerous reports of IMS being introduced into new areas throughout the world, but relatively few are in tropical locations. It has been suggested that this is an artefact of our lack of knowledge species present in the megadiverse tropics and a lack of IMS surveys. The Pilbara in northern Western Australia (WA) is used as a case study to examine these questions. The area is at high risk of IMS because of extensive international shipping. A detailed literature search of marine biodiversity studies developed a database of 5,532 species recorded in the Pilbara. There have been numerous surveys for species on the Australian national and WA IMS lists but only one, the ascidian Didemnum perlucidum Monniot, 1983, has been found.