The epifaunal and infaunal assemblages associated with Caulerpa taxifolia in the Port River/Barker Inlet estuary of Adelaide, South Australia were compared to those associated with the co-occurring seagrass Zostera muelleri. Both taxa contained an abundant and diverse fauna, but with substantial differences between them. In particular, ophiuroids (brittle stars) were abundant in Caulerpa, but almost absent from Zostera. Crustaceans, mostly amphipods, and annelids, mostly polychaetes, were abundant in both Caulerpa and Zostera, but the families present differed substantially. Taxa that dominated in Caulerpa include the amphipods: Amphithoidae, Corophiidae, and Talitridae; and the polychaetes: Cirratulidae, Nephtyidae, and Nereididae. Zostera was dominated by the polychaetes: Capitellidae; amphipods: Caprellidae; isopods: Sphaeromatidae; and Neballidae. Some taxa (arthropods, nemerteans, and echinoderms) had their peak abundance during summer, when Caulerpa biomass was highest, while others did not seem to respond to changes in Caulerpa biomass. Overall, epifauna were 4-9 times more abundant in Caulerpa than Zostera, while infauna were slightly more abundant in Zostera, indicating that at least in South Australia, Caulerpa provides a functional habitat for a diverse array of taxa.