Christmas tree worms (Spirobranchus spp.) are prominent sessile organisms inhabiting hermatypic corals in tropical and sub-tropical reefs. Until recently, most of the larger Spirobranchus species were considered to be in obligatory associations with live hermatypic corals. However, recent studies indicate that some Spirobranchus species can build tubes on artificial substrate as well and that others may show preferences for using specific species of corals and hydrozoans as substrates. In the present study, we conducted a survey of Spirobranchus spp. substrate preference in the Gulf of Eilat. We found seven morphotaxa of Spirobranchus, of which two may be a single new species. We show that Spirobranchus taxa differ not only in their morphology, but also in their substrate use. Our results demonstrate that the ecological niche of Spirobranchus is species-specific, and a putative innate preference exists for some substrates.
