Zanclea is a genus of small hydroids that specializes at living on other marine creatures like corals, anemones, sponges and bryozoans. About five years ago we visited a healthy stony coral reef aquarium Seattle that had some staghorn coral colonies that were well populated with these tiny hairlike hydroids living on them; not all the Acropora were affected, mostly the large staghorns, but the hydroids did not appear to be causing any damage. Ever since that first encounter with the little hairlike hydroids we have seen them on a few more occasions in fresh and old coral alike and we’ve always wondered what they were, and a recent scientific publication has finally documented the Zanclea hydroids living on Acropora corals.
Olga Pantos and John Bythell were first to document the association of a new species of hydroid, Zanclea margaritae, with the common staghorn coral, Acropora muricata (= formosa). Although the researchers describe Zanclea as a commensal symbiont in the wild, with less biodiversity to keep them in check in an aquarium we’re taking the liberty of calling Zanclea a pest. If you’ve seen them before, you’ll agree that anything that grows on a coral and detracts from how we want it to look is a pest – seriously, looks like a bunch of equally spaced stubble on the surface of an Acro, gross.
Another recent paper by Hirose & Hirose describes another new species, Zanclea sango from the Sea of Japan which was discovered growing on two different species of Pavona and a Psammocora species. Thankfully, we don’t believe that Zanclea is a threat to aquarium stony corals the way that the Acro Eating Flatworm Amakusaplana acroporae is. Where we’ve seen “large” populations of Zanclea was in the case of large healthy and growing Acropora colonies so there was clearly little detriment there and we’ve also seen Zanclea on fresh Acro colonies imported from the wild which disappeared after a few weeks in captivity with no explanation for their disappearance.