Do introduced endosymbiotic dinoflagellates 'take' to new hosts?

In a recent communication by Stat and Gates (Biol Invasions 10: 579-583, 2008), discovery of a symbiotic combination involving the coral Acropora cytherea and the dinoflagellate endosymbiont, Symbiodinium A1 (Symbiodinium microadriaticum, Freudenthal sensu stricto) in the Northwest Hawaiian Islands was interpreted to be the result of a 'recent' introduction. While introductions of symbiotic dinoflagellates have occurred and are occurring, the authors' conclusion was made without sufficient information about the geographic range and host specificity exhibited by A1. The only direct genetic analysis of symbionts from the putative host vector, a jellyfish in the genus Cassiopeia sp., from Kaneohe Bay on the Island of Oahu, found that it contained a different symbiont species, A3. Furthermore, Stat and Gates (Biol Invasions 10: 579-583, 2008) did not consider the importance of host-symbiont specificity in preventing the establishment of a foreign symbiont species. In comparison to A. cytherea, A. longicyathus on the southern most Great Barrier Reef also hosts Symbiodinium A1 and a closely related endemic, A1a. Instead of assuming that A. cytherea has an unnatural association, a practical explanation is that long-term ecological and evolutionary processes influenced by local environments underlie the unusual, but not unprecedented finding of a Pacific acroporid associating with Clade A Symbiodinium spp.