Chromera Velia: Coral Symbiont Or Parasite?

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Galaxea, Journal of Coral Reef Studies 15: 15-16（2013）

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Chromera velia: Coral symbiont or parasite?

V.R. CUMBO* and A.H. BAIRD

ARC CoE Coral Reef Studies, James Cook University, Townsville, 4810

* Corresponding author: V.R. Cumbo E-mail: [email protected]

Communicated by Saki Harii (Ecology Editor)

Keywords apicomplexan, coral reef, larval ecology, symbiosis

The discovery of a novel alga, Chromera velia, has gen erated much interest because it is a missing link between the non-photosynthetic apicomplexan parasites and dino flagellates, which includes the coral endosymbiont Sym biodinium (Moore et al. 2008). Janouškovec, this new algal species has only been found in association with corals, having now been isolated from multiple coral species from a range of reefs worldwide (Moore et al. 2008; Cumbo et al. 2012; Janouskovec et al. 2012). C. velia can be endosymbiotic in coral larvae (Cumbo et al. 2012), and can also persist in culture, however, due to its close relationship to apicomplexans it may become para sitic under some conditions (Oborník et al. 2011). In sup port of this potential shift to parasitism, organelles puta tively specialised for cell or host invasion are formed when C. velia is free-living and motile (Oborník et al. Fig. 1 Two Chromera velia clumps fluorescing bright red col 2011). liding with an Acropora digitifera larva. The larger clump ap During coral larval infection experiments with C. velia pears to be digesting the ectoderm. The smaller clump has pos sibly been internalised. Green and red fluorescence proteins are (Cumbo et al. 2012), free-living C. velia occasionally formed also evident in the larva. clumps containing numerous cells. Two such clumps came into contact with a coral larva. The cells penetrated the larva, with the larva responding to the contact by contracting around the larger clump (Fig. 1). Within five minutes, the larger clump appeared to be digesting the larval epidermis suggesting that the free-living C. velia were parasitic (Fig. 1). This observation, while only preliminary, is significant because it is the first evidence that C. velia might behave as a parasite. Transitions from commensal to parasite are common in other symbioses such as bacteria inhabiting sponges (Thacker & Freeman 2012). 16 Cumbo and Baird: Chromera velia: Coral symbiont or parasite?

Acknowledgments This study was partially supported by the 21st Century Center of Excellence (COE) program of the University of the Ryukyus and the Endeavour Foundation. We thank C. Marquis for assistance with the culture of C. velia.

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