Morphological variation among populations of an invasive jellyfish

The Australian spotted jellyfish Phyllorhiza punctata appeared in the Northern Gulf of Mexico in spectacular numbers during the summer of 2000. P. punctata was first described from Eastern Australia, although its native habitat probably extends across Northern Australia and into SE Asia. Among invasive marine species, P. punctata has a relatively well-documented history of invading tropical and subtropical environments. Despite this, there is no direct evidence of translocation routes or the mechanisms by which translocation has occurred. The invasion of the Northern Gulf of Mexico has been theorized to represent an inevitable distributional shift of an invasive hub population in the Caribbean Sea facilitated by periodic oceanographic connections between the regions, or by the transportation of benthic scyphistomae on the hulls of ships. Regardless of the translocation mechanism, the relatively close geographical proximity of the Caribbean to the Northern Gulf of Mexico makes this theory conceptually appealing. Based on a 'hub and spoke' model of marine bio-invasion, we postulated that populations of P. punctata from regions more geographically distant than those from the Caribbean and the Gulf of Mexico have been separated for longer periods of time; therefore, populations from the Caribbean and the Gulf of Mexico would bear greater morphological similarity to each other than to those of other regions due to higher levels of underlying genetic relatedness. We used multivariate analyses to compare the morphological similarity of 6 populations of R punctata distributed between the Gulf of Mexico, Caribbean and the east and west coasts of Australia. Contrary to our expectations, analyses showed that populations from the Caribbean and the Gulf of Mexico are the least similar to each other. The analyses suggest that the invasive population in the Gulf of Mexico is most likely to have originated from geographically disparate populations in either Australia or the west coast of the United States. Populations from Australia and the west coast of the United States were the most similar to each other, while the Caribbean population bore the least similarity to all other populations.