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A novel reef coral symbiosis

Lookup NU author(s): Dr Olga Pantos, Professor John BythellORCiD


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Reef building corals form close associations with unicellular microalgae, fungi, bacteria and archaea, some of which are symbiotic and which together form the coral holobiont. Associations with multicellular eukaryotes such as polychaete worms, bivalves and sponges are not generally considered to be symbiotic as the host responds to their presence by forming physical barriers with an active growth edge in the exoskeleton isolating the invader and, at a subcellular level, activating innate immune responses such as melanin deposition. This study describes a novel symbiosis between a newly described hydrozoan (Zanclea margaritae sp. nov.) and the reef building coral Acropora muricata ( =A. formosa), with the hydrozoan hydrorhiza ramifying throughout the coral tissues with no evidence of isolation or activation of the immune systems of the host. The hydrorhiza lacks a perisarc, which is typical of symbiotic species of this and related genera, including species that associate with other cnidarians such as octocorals. The symbiosis was observed at all sites investigated from two distant locations on the Great Barrier Reef, Australia, and appears to be host species specific, being found only in A. muricata and in none of 30 other species investigated at these sites. Not all colonies of A. muricata host the hydrozoans and both the prevalence within the coral population (mean = 66%) and density of emergent hydrozoan hydranths on the surface of the coral (mean = 4.3 cm−2, but up to 52 cm−2) vary between sites. The form of the symbiosis in terms of the mutualism–parasitism continuum is not known, although the hydrozoan possesses large stenotele nematocysts, which may be important for defence from predators and protozoan pathogens. This finding expands the known A. muricata holobiont and the association must be taken into account in future when determining the corals’ abilities to defend against predators and withstand stress.

Publication metadata

Author(s): Pantos O, Bythell JC

Publication type: Article

Publication status: Published

Journal: Coral Reefs

Year: 2010

Volume: 29

Issue: 3

Pages: 761-770

Print publication date: 20/04/2010

ISSN (print): 0722-4028

ISSN (electronic): 1432-0975

Publisher: Springer


DOI: 10.1007/s00338-010-0622-5


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Funder referenceFunder name
GEF-World Bank Bleaching Working (BWG)
NE/E006949/1Natural Environment Research Council, UK